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Industrial bio-lubricants performance and characterization Elemsimit, Abdulhamid A. 2013

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INDUSTRIAL BIO-LUBRICANTS PERFORMANCEAND CHARACTERIZATIONbyAbdulHamid A. ElemsimitA THESIS SUBMITTED IN PARTIAL FULFILLMENT OFTHE REQUIREMENTS FOR THE DEGREE OFMASTER OF SCIENCEinThe Faulty of Graduate Studies(Mehanial Engineering)THE UNIVERSITY OF BRITISH COLUMBIA(Vanouver)Marh 2013? AbdulHamid A. Elemsimit 2013AbstratAbstratThe general trend towards the use of high performane lubriants and environmentallyfriendly produts supports the design of new industrial lubriants. Therefore, thereare good pratial reasons to extend the researh related to lubriation. Bio-oils, aspromising growing substitutes for mineral oils, need more researh to deal with new andinherited problems. Meanwhile, there is no omplete understanding of the lubriationphenomenon, nor a omplete rheologial haraterization of oil lubriants. This researhis an eort to study industrial bio-ubriants and to develop a more omprehensive ap-proah, at the same time orrelating their rheologial and tribologial behavior.Dierent ommerial anola oil based lubriants were studied using dierent teh-niques. For validation and omparison, engine oil, silione oil and mineral hydraulioil were tested. Bio-lubriants exhibited onstant visosity at both moderate and highshear rates and shear thinning at low shear rates and temperatures below 30 degrees Cel-sius. Frequeny sweep tests revealed a signiant visoelastiity of bio-lubriant whihdeveloped over time.Time dependene, struture reovery, gap size eet, surfatant behavior, and geom-etry's material inuene were all investigated. A high pressure ell and a polarized lightmirosope oupled with the rheometer were used to investigate the bio-lubriants.Thermal analysis was onduted using a dierential sanning alorimeter. Severaltransition points were identied in the range of temperatures from -30 to 100 degreesCelsius, and the results have been onneted to the visoelasti behavior.Dierent tribologial tests were used to investigate the lubriity of lubriants and bio-lubriants added by liquid rystals. The oeient of frition, at tested temperatures,and the wear rate were observed over time. Adding two perent of ioni liquid rystalsimproved the wear resistane of the oil, but the bio-lubriant had the lowest oeientof frition.iAbstratThis researh ould be onsidered as pioneer work. An attempt was made to ahieveprofound perspetive mathing between rheometry, tribology and thermal analysis. Someassumptions explaining the rheologial and tribologial behavior were hypothesized andassoiated with arguments and disussions. Based on, Imaginary senario of bio-hydraulioil behavior within a small gap was visualized.iiPrefaeThis thesis was written by Abdul-Hamid Elemsimit under the supervision and guidaneof Dr. Dana Greov, who provided the topis for this researh: the rheologial harater-ization of bio-lubriants; the tribologial performane of bio-lubriants; the rheologialand tribologial impats of liquid rystal additives on bio-lubriants; and the thermalanalysis of bio-lubriants.All the rheometery experiments were onduted in the Polymer Rheology lab at theUniversity of British Columbia. The author both designed and performed the experi-ments, as well as prepared the used solutions.Dr. Louise Creagh, of the University of British Columbia, failitated and instrutedusing the Bio Thermodynamis lab, where the TA experiments were done. The authordesigned the experiments, prepared the samples, and performed the experiments.For the four ball tests, onduted by the National Researh Counil (NRC), Vanou-ver, the author provided the experiment onditions based on international standards,and examined the sars in the Eletron Mirosope Laboratory, University of BritishColumbia, under the supervision of a speialist tehniian. In a related work, the authorprepared the samples, deided the testing onditions, and onduted the experiments ofpin-on-disk in the Pulp and Paper Centre, at the University of British Columbia (UBC).iiiTable of ContentsAbstrat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iPrefae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iiiTable of Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ivList of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xList of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiList of Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvList of Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xviiiAknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xixDediation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xx1 Introdution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Motivations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.3 Objetives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.4 Sope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41.5 The Lubriants Industry . . . . . . . . . . . . . . . . . . . . . . . . . . . 61.6 Future Lubriants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6ivTable of Contents1.7 Canola Oil in Canada's Eonomy . . . . . . . . . . . . . . . . . . . . . . 81.8 Physial and Chemial Properties of Canola Oil . . . . . . . . . . . . . . 91.9 Additives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101.10 Lubriation Regimes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121.11 Surfatant Behaviour . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141.12 Liquid Crystals [2, 22? . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152 Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172.1 Literature Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172.1.1 Rheometry of Bio-lubriants and Low Visous Materials . . . . . 172.1.1.1 Rheometry of Bio-oils . . . . . . . . . . . . . . . . . . . 172.1.1.2 Rheometry of Low Visous Liquids . . . . . . . . . . . . 182.1.1.3 Rheometry of More Visous Related Materials . . . . . 192.1.1.4 Rheometry of Engine Oils . . . . . . . . . . . . . . . . . 192.1.2 Rheometry Errors . . . . . . . . . . . . . . . . . . . . . . . . . . 202.1.3 Mathematial Model . . . . . . . . . . . . . . . . . . . . . . . . 202.1.4 Thermal Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . 212.1.5 Bio-lubriants Tribology . . . . . . . . . . . . . . . . . . . . . . . 222.1.6 Liquid Crystal Additives . . . . . . . . . . . . . . . . . . . . . . . 222.1.6.1 Liquid Crystals with Water . . . . . . . . . . . . . . . . 222.1.6.2 Liquid Crystals with Mineral Oils . . . . . . . . . . . . 232.1.6.3 Liquid Crystal with Bio-oils . . . . . . . . . . . . . . . 232.2 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242.3 Rotary Rheometer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252.4 Measuring Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282.5 Short Amplitude Osillation Shear (SAOS) . . . . . . . . . . . . . . . . 302.6 Mathematial Model [80? . . . . . . . . . . . . . . . . . . . . . . . . . . 31vTable of Contents2.7 Unertainty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 342.7.1 Software Error Measurements [81? . . . . . . . . . . . . . . . . . 342.7.1.1 Steady State . . . . . . . . . . . . . . . . . . . . . . . . 342.7.1.2 Harmoni Distortion . . . . . . . . . . . . . . . . . . . . 352.7.1.3 Inertial Eets Dominating . . . . . . . . . . . . . . . . 352.7.2 Gap Auray . . . . . . . . . . . . . . . . . . . . . . . . . . . . 352.7.3 Auray Versus Shear Rate . . . . . . . . . . . . . . . . . . . . 362.7.4 Repeatability . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373 Rheologial Charaterization . . . . . . . . . . . . . . . . . . . . . . . . . 383.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 383.2 Visometery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 393.2.1 Visosity Versus Temperature . . . . . . . . . . . . . . . . . . . . 393.2.2 Moderate Shear Rate . . . . . . . . . . . . . . . . . . . . . . . . 423.2.3 High Shear Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . 443.2.4 Yield Stress . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 453.3 Small Amplitude Osillatory Shear (SAOS) . . . . . . . . . . . . . . . . 463.3.1 Osillation Amplitude . . . . . . . . . . . . . . . . . . . . . . . . 483.3.2 Time Dependeny of the Elasti Modulus . . . . . . . . . . . . . 483.3.3 Frequeny Sweep . . . . . . . . . . . . . . . . . . . . . . . . . . 493.4 Low Shear Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 513.5 Gap Size Inuene on Elasti Modulus . . . . . . . . . . . . . . . . . . 523.6 The Deliate Struture of Bio-hydrauli Oil . . . . . . . . . . . . . . . . 543.7 Struture Reovery of Bio-hydrauli Oil . . . . . . . . . . . . . . . . . . 553.8 Rheometry as Tehnique to Study Surfatant Behavior . . . . . . . . . 583.8.1 Impat of Surfae Conditions of the Geometry on Rheologial Be-havior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59viTable of Contents3.8.2 Impat of Geometry's Material on Rheologial Behavior . . . . . 603.9 Polarized Light Mirosopy . . . . . . . . . . . . . . . . . . . . . . . . . 633.10 Liquid Crystal Additives . . . . . . . . . . . . . . . . . . . . . . . . . . 663.11 High Pressure Rheology . . . . . . . . . . . . . . . . . . . . . . . . . . . 683.12 Conlusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 704 Thermal Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 724.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 724.2 Experimental Setup Apparatus . . . . . . . . . . . . . . . . . . . . . . . 734.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 744.3.1 Repeatability and Reversibility . . . . . . . . . . . . . . . . . . . 744.3.2 Sample Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 744.3.3 Transition Points . . . . . . . . . . . . . . . . . . . . . . . . . . 754.3.4 Dierent Bio-lubriants . . . . . . . . . . . . . . . . . . . . . . . 784.3.5 Impat of Liquid Crystal Additives on DSC . . . . . . . . . . . . 784.3.6 Comparing Between DSC and Rheologial Behavior . . . . . . . 804.4 Conlusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 815 Tribology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 825.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 825.2 Compression Investigation of Bio-lubriant Lubriity . . . . . . . . . . . 835.2.1 Apparatus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 845.2.2 Experimental Setup . . . . . . . . . . . . . . . . . . . . . . . . . 845.2.3 Repeatability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 855.2.4 Sars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 855.2.5 Coeient of the Frition: . . . . . . . . . . . . . . . . . . . . . 875.3 Liquid Crystals as Additives to Improve Lubriity . . . . . . . . . . . . 89viiTable of Contents5.3.1 Samples and Experimental Setup . . . . . . . . . . . . . . . . . 895.3.1.1 Lubriants: . . . . . . . . . . . . . . . . . . . . . . . . . 895.3.1.2 Preparation of 10% of Cholesteryl Chloride: . . . . . . 895.3.1.3 Preparation of 2 % of Tetrauoroborate . . . . . . . . . 905.3.1.4 Pair of Frition . . . . . . . . . . . . . . . . . . . . . . . 905.3.1.5 Experimental Setup . . . . . . . . . . . . . . . . . . . . 905.3.2 Apparatus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 915.3.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 925.3.3.1 Temperature . . . . . . . . . . . . . . . . . . . . . . . . 925.3.3.2 Test Quality . . . . . . . . . . . . . . . . . . . . . . . . 935.3.3.3 Wear . . . . . . . . . . . . . . . . . . . . . . . . . . . . 945.3.3.4 Coeient of the Frition . . . . . . . . . . . . . . . . 975.4 Conlusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 986 Conlusion and Future Work . . . . . . . . . . . . . . . . . . . . . . . . 1006.1 Ahievements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1006.2 Hypotheses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1006.3 Questions Raised . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1046.4 Conlusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1056.5 Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1066.5.1 Rheometer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1066.5.2 Tribometer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1076.5.3 Mathematial Model . . . . . . . . . . . . . . . . . . . . . . . . 1086.5.4 Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109viiiTable of ContentsAppendiesA Surfae Tension . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121B Density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123C Thermal Expansion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124ixList of Tables1.1 Chemial omposition of anola oil . . . . . . . . . . . . . . . . . . . . . 111.2 Triaylglyerol omposition of anola oil . . . . . . . . . . . . . . . . . . 113.1 Constants for double exponential regression . . . . . . . . . . . . . . . . 423.2 Summery of struture reovery tests on bio-hydrauli oil . . . . . . . . . 564.1 Comparison transition points [58,61,34? . . . . . . . . . . . . . . . . . . 774.2 Comparison between hemial omposition of anola oil and undatus [13,14, 60? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 785.1 Four-ball test onditions . . . . . . . . . . . . . . . . . . . . . . . . . . . 855.2 Summarized results of four-ball test . . . . . . . . . . . . . . . . . . . . . 855.3 Pin-on-disk test onditions . . . . . . . . . . . . . . . . . . . . . . . . . 915.4 The measurements of the sars on the disks . . . . . . . . . . . . . . . . 955.5 Frition oeient for pin-on-disk tests . . . . . . . . . . . . . . . . . . . 98xList of Figures1.1 Researh goal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41.2 Researh plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51.3 Fate of global lubriants after use in 2009 . . . . . . . . . . . . . . . . . . 71.4 Utilizations of anola oil . . . . . . . . . . . . . . . . . . . . . . . . . . . 91.5 Moleular Struture of the main ompositions in anola oil [14, 15? . . . . 101.6 Stribek's urve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131.7 Energy losses in the internal ombustion engine . . . . . . . . . . . . . . 141.8 Adsorption mehanisms in fatty aids on steel surfaes . . . . . . . . . . 141.9 Nemati and smeti order of liquid rystalline phases . . . . . . . . . . . 162.1 Greenland oils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242.2 Liquid rystals additives . . . . . . . . . . . . . . . . . . . . . . . . . . . 252.3 Calibrating oil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252.4 Illustrative shemati diagram of single head design of a rotary rheometer 262.5 Kinexus rheometer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272.6 Parallel plate measuring system . . . . . . . . . . . . . . . . . . . . . . . 282.7 Time dependant funtions of SAOS, (shear rate, strain and stress ) . . . 302.8 Visoelasti material is resembled to mehanial model of spring and dash-pot in series . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332.9 Visosity orretion due to the gap error, bio-hydrauli oil at 20?C . . . . 362.10 Visosity versus shear rate, standard oil . . . . . . . . . . . . . . . . . . . 37xiList of Figures3.1 Visosity versus temperature of dierent oils . . . . . . . . . . . . . . . . 403.2 Failure of single exponential funtion . . . . . . . . . . . . . . . . . . . . 413.3 Credibility of double exponantial funtion in representing the visosityhange with respet to temperature of bio-hydrauli oil . . . . . . . . . . 413.4 Visosity versus shear rate at dierent temperatures. a) bio-hydrauli oil.b) mineral hydrauli oil. ) bio-gear oil d) bio-hain saw oil . . . . . . . . 433.5 Visosity at high shear rate, bio-hydrauli and engine oils . . . . . . . . . 443.6 Normal fore at high shear rate, bio-hydrauli and engine oils . . . . . . 453.7 Yield stress in bio-hainsaw oil . . . . . . . . . . . . . . . . . . . . . . . 463.8 Illustrative input signal of multi osillation proedure . . . . . . . . . . . 473.9 Linear visoelastiity limit of bio-hydrauli oil at 1Hz frequeny . . . . . 483.10 Time dependene of the dynami shear modulus G? for dierent oils at0?C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 493.11 Frequeny sweep of bio-hydrauli oil at dierent temperatures . . . . . . 503.12 Storage modulus of bio-hydrauli oil at 1 Hz versus temperature . . . . . 503.13 Maxwell model ts bio-hydrauli oil's result at 0?C . . . . . . . . . . . . 513.14 Shear thinning behavior of bio-hydrauli oil . . . . . . . . . . . . . . . . 523.15 Eet of gap size on elasti and loos moduli, bio-hydrauli oil at 0?C and1 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 533.16 Eet of gap size on shear moduli, bio-hainsaw oil at 0?C and 1 Hz . . . 543.17 The input signal of multi proedure experiment (3.18) . . . . . . . . . . . 553.18 Visosity of bio-hydrauli oil due to sequential multi shear test . . . . . . 563.19 Struture reovery of bio-hydrauli oil at 0.4 mm gap . . . . . . . . . . . 573.20 Struture reovery of bio-hydrauli oil at 0.2mm gap . . . . . . . . . . . 583.21 Elasti modulus versus time at gap 0.2 mm and frequeny 4Hz . . . . . . 59xiiList of Figures3.22 Frequeny sweep test of bio-hydrauli oil at 0?C, and with dierent ge-ometry materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613.23 Frequeny sweep test of 2%ILC at 0?C with dierent geometry materials,the sample was replaed . . . . . . . . . . . . . . . . . . . . . . . . . . . 623.25 Pitures of the samples after tests on the lower plate . . . . . . . . . . . 623.24 Frequeny sweep test of 2% ILC at 0? C; the sample was squeezed . . . . 633.26 Anton Paar, polarized light mirosope . . . . . . . . . . . . . . . . . . . 643.27 Polarized light mirosope pitures on Anton Paar rheometer . . . . . . 643.28 Osillatory temperature sweep, loos modulus (G) . . . . . . . . . . . . 673.29 Osillatory temperature sweep, elasti modulus (G') . . . . . . . . . . . 673.30 Anton Paar high pressure ell (reprodued image) [83? . . . . . . . . . . 683.31 Visosity of bio-hydrauli oil under pressure of CO2 . . . . . . . . . . . . 693.32 Bio-hydrauli oil visosity versus CO2 pressure drop, maximum pressure3.6 MPa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 693.33 Visosity of bio-hydrauli oil under pressure of N2 . . . . . . . . . . . . . 703.34 Imaginary simplied senario of bio-hydrauli oil rystallization within asmall gap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 714.1 The alorimeter used, MC-DSC4100 . . . . . . . . . . . . . . . . . . . . . 734.2 The DSC heating and ooling urves of bio-hydrauli oil . . . . . . . . . 754.3 DSC ooling urves for dierent mass samples of bio-hydrauli oil . . . . 764.4 Transition points on heating the DSC urve of bio-hydrauli oil . . . . . 774.5 DSC ooling urves of dierent bio-oil samples . . . . . . . . . . . . . . 794.7 DSC ooling urves of bio-hydrauli oil plus liquid rystal additives . . . 794.6 DSC heating urves of bio-hydrauli oil plus liquid rystal additives . . . 804.8 Comparing the SAOS and DSC tests on bio-hydrauli oil (The heat owaxis is in reverse order for the purposes of lariation) . . . . . . . . . . 81xiiiList of Figures5.1 Shemati drawing demonstrating the adhesive frition mehanism . . . . 835.2 Falex-6 (multi speimen wear tester) . . . . . . . . . . . . . . . . . . . . 845.3 Sanning Eletron Mirosope (SEM) . . . . . . . . . . . . . . . . . . . 855.4 Four-ball test sars aptured using SEM . . . . . . . . . . . . . . . . . . 865.5 Frition oeient versus time for bio and mineral hydrauli oils . . . . . 875.6 Pin-on-disk setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 915.7 Temperature versus time for pin-on-disk tests . . . . . . . . . . . . . . . 935.8 Distribution of the frition oeient and LVDT readings around theirular path at the revolution 18x103. . . . . . . . . . . . . . . . . . . . 945.9 LVDT reading versus distane for 5 hours . . . . . . . . . . . . . . . . . 955.10 Proles of the sars on the disks . . . . . . . . . . . . . . . . . . . . . . . 965.11 Disseting mirosope and digital mirosope . . . . . . . . . . . . . . . . 965.12 Pin-on-disk sars, a) shemati drawing for the mathing between balland disk; b) sar on ball, ) ball and disk; d) sar on disk . . . . . . . . 975.13 Frition oeient Versus time, Pin-on-disk tests . . . . . . . . . . . . . 98xivList of SymbolsCp heat apaityf frition foreG? storage modulusG?? loss modulusG? omplex mudlush gap sizehm measured gapM measured torqueN normal forep ontat presurepo presure in the enter of the ontat areaQ heatR the radius of the geometryro the radius of ontating areaSSCs steady state measurement in ontrolled stressxvList of SymbolsSSCr steady state measurement in ontrolled rate modet timeti integration timets sample time? angular veloity? heating rate?A shear amplitude?o shear rate?oR maximum shear rate at the rim of the Parallel plate geometry=?o shear rate tensor? phase angle?g gap error?f error in measured frition fore? shear visosity?o zero shear visosity?m measured visosity? relaxation time? Coeient of Frition? shear stressxviList of Symbols?oR maximum shear stress at the rim of the Parallel plate geometry=? stress tensor? angular frequenyxviiList of AbbreviationsASTM Amerian Soiety for Testing and MaterialsCFD Computational Fluid DynamisDSC Dierential Sanning CalorimetryILC Ioni Liquid CrystalsISO International Standards OrganizationLC Liquid CrystalsLC50 Lethal Conentration testLD50 Lethal Dose testLVDT Linear Variable Dierential TransformerNRC the National Researh CounilSAM Self Assembled MonolayerSAOS Short Amplitude Osillation ShearTA Thermal AnalysisUBC University of British ColumbiaVI Visosity IndexxviiiAknowledgementsI would like to express my appreiation and thanks to everyone helped me with thisresearh. To my supervisor, Dr. Dana Greov for supervising me during the researhperiod, for reading the thesis and giving appreiative feedbak on. Also, the thanks is ex-tended to the examining ommittee members, Dr Farrokh sassani and Dr Ian A. Frigaard.To Green Land Company, whih provided the samples and sponsored this researh, par-tially. To Je Mentel for prompt kind tehnial support using Kinexus rheometer. ToDr. Louise Creagh for failitating and training at the Bio-Thermodynamis lab. To Dr.Savvas Hatzikiriakos for failitating using pressure ell and Anton Paar rheometer.xixDediationTo my fatherwho believes in knowledge and appreiates the eduation as nobodydoes; who has never imposed any axioms on my thoughts or asked me to stop askingwhy; and he was the stronger motivator to be in this position.xxChapter 1Introdution1.1 OverviewThe general trend towards the use of high performane lubriants and environmentallyfriendly produts supports the design of new industrial lubriants. Therefore, thereare good pratial reasons to extend the researh related to lubriation. Bio-oils, aspromising growing substitutes for mineral oils, need more researh to deal with new andinherited problems. In terms of the tested material and similar studies, this researhould be onsidered as pioneer work.1.2 MotivationsConsiderable appliations for the subjet of this study are worth the researh on thisarea, eonomially. The world market for lubriants will be presented in this hapter,while the following is a list of eonomi motivations:? Lubriants have a large growing market.? Implementing lubriating tehnologies will lead to more eient systems.? There is a renewable demand for speial purpose lubriants; among them are bio-degradable lubriantsBesides, there are more motivations to use bio-lubriants speially:11.2. Motivations? Bio-oils ome from sustainable resoures? They have advantage over mineral oil regarding environmental and health risks? Legislations are putting more restritions on polluting tehnology? Using bio-oils dereases the liability insurane osts that ome with using or pro-duing harmful materials [1?? Using bio-oils dereases disposable osts [1?? Bio-oils have a high visosity index, and very good lubriity.? Improving a ompany's publi image? It diversies the uses of rapeseedsAll of the mentioned advantages of using bio-oils as lubriants do not ome withouta prie. There is not enough supply from vegetable oils to subtitute the mineral oilsnowadays. Furthermore, they have poor oxidation resistane. Regardless of the eo-nomi motivations, there are number of aademi motivations that enourage researhon lubriants generally and bio-lubriants speially:? The rheologial haraterization studies on oil lubriants are still limited.? There is still a gap between real ases and mathematial models.? There has been no mathematial model developed speially for lubriants.? The lubriating phenomenon is not yet fully understood.? There is a gap between miro & marosopi, and rheologial & tribologial studies? Not all the studies on mineral oils an be generalized to bio-oils; they dier inmany aspets.21.3. Objetives? Continuing innovationWhile onstitutive equations fail to represent the real ase of visoelasti lubriation,quantitatively, the experimental studies are inadequate. Experimental work on lubri-ants is hallenging. The extreme onditions, suh as the very high shear rate, veryhigh pressure, and very narrow gap, needed to make the measurements an make it verydiult. Where learane of 50 mirons is a large distane in lubriation, the usual gapin a rotary rheometer varies from 0.5 to 1 mm. Nonetheless, the nano-tehnologies, suhas eletron mirosopy, atomi fore mirosopy, and x rays, have managed to reah newlevels of researh, espeially understanding the Self-Assembled Monolayer (SAM). How-ever, it is not easy to use these tehnologies under harsh onditions. In spite of a generaltrend to welome every sustainable and environmentally safe tehnology, the ompetitivequality of bio-lubriants still needs to be proven, as they are yet an unfamiliar produt toonsumers. Bio-oils also have ompletely dierent hemial ompositions from mineraloils. This means that not all of the improving additive pakages that worked well withmineral oils are ompatible with bio-oils.1.3 ObjetivesFigure (1.1) illustrates the idea behind this researh. The ultimate goal is formulatinga more redible model based on experimental work done speially on lubriants. Thenew model should approah the real ase more exatly. It should show a math amongthe dierent views, suh as: rheology, tribology, and mirosopy. The aimed modelshould ll the present gaps and answer some raised questions.Aordingly, the objetives of the present researh are listed as follows:? To haraterize bio-lubriants Rheologially? To evaluate the tribologial performane of bio-lubriants31.4. SopeFigure 1.1: Researh goal? To investigate the ompatibility of liquid rystals additives with bio-lubriants? Understanding the boundaries and hydrodynami lubriation mehanisms in bio-lubriation1.4 SopeThis work is an attempt to ahieve the drawn goal using available resoures. Figure(1.2) shows the plan of this work.Later in this hapter, some introdutory surveys about the lubriants market andanola oil were presented. Further, some physial bakground about related topiswere explained briey. The Literature Review was inluded in the seond hapter, themethodology. The rest of that hapter was devoted to the rheometery methods. Forthe purpose of sequentiality, the desriptions of the tribologial and thermal analysesexperiments will be postponed to hapters 4 and 5. The researh tools were lassiedinto two types of tools: experimental and theoretial. The main tool in this researhwas the rotary rheometer. The rheometrial experiments are desribed in hapter 3.41.4. SopeFigure 1.2: Researh planThe ontrolled experimental onditions inluded shear, temperature, geometry materi-als, pressure, and surrounding medium. As well, the lubriants were examined under apolarized light mirosope. After the behavior of the interesting oils beame more reog-nizable, a dierential sanning alorimeter (DSC) was used to support the assumptionswe had begun to build. Chapter 4 is where the thermal analysis work was presented.The lubriity of the bio-lubriant was the ultimate goal therefore the tribologial per-formanes of bio-hydrauli oil and liquid rystal additives were presented in Chapter 5.Beause all the right paths should end in one destination, we tried to onnet the resultsin the last three hapters as muh as possible. In the last hapter (Chapter 6) , theonlusion and future work were presented. Even though the assumptions built werebased on onsistent experimental results and supported by the literature, we annotall it onrmed. Thus, we organized the onlusions in the form of hypothesises andarguments.51.5. The Lubriants Industry1.5 The Lubriants IndustryDespite the fat that frition is one of the fores that keeps the various elements of theuniverse attahed to eah other, tremendous eort is exerted to redue and overome thisnatural frition, in order to move things with less energy. Where half the onsumptionenergy is dissipated as frition [2?, another researher estimated that the energy lostdue to frition ould be saved, based on present tehnologies, with about 0.4% of thegross domesti produt in Western industrialized ountries [3?. On the other hand,lubriation is one of the oldest and most widely used tehniques employed to reduefrition. Aording to a World Lubriants report from the Freedonia Group [4, 5?[4, 5?,the global demand on lubriants will reah 40.5 MT in 2012, with an inreasing rate of1.6%. About 90% of the base-oils, whih represent from 70 to 99% of all the lubriants,ome from petrol. Therefore, 1% of world petrol onsumption goes to this industry.Syntheti oils will ontribute 10 % of base oils by 2015 [6?. Bio-lubriants share 1% ofthe market, with a growth rate of 5-8 % [7?.1.6 Future LubriantsThe future lubriant will be superior in performane, environmentally safe, sustainable,and ompliant with modern legislations. The higher visosity index and lubriity haveallowed for a derease in the required visosity. This means lower energy losses. Inaddition, hemial stability and less volatility will derease the inidents of leakage andfrequent hanges. These developments have already taken plae in the present produtsof today's market. With a greater fous on the environmental aspets of new produts,about 50 perent of a used lubriant returns bak to the environment [6?, due to evap-oration, leakages, spills, and other mishaps, whih pollute the air, soil and water. (Seeg. 1.3) For this reason and others, there is a general trend in the world, among deision61.6. Future Lubriantsmakers and pubi mediums, to follow more environmental approahes in industry. Thistrend is being translated into legislation day by day, adding more restritions on on-ventional produts, suh as mineral lubriants, espeially in some appliations, wherethe damage has beome intensied, like losed waters, lakes and rivers.Figure 1.3: Fate of global lubriants after use in 2009Biodegradability and lethal dose onentration (LD50, LC50) tests are importantmeasurements to deide the lubriants' ompliane with the environment restritions.The biodegradability test was dened under dierent international standards, ASTM,suh as D6731, D5864 and D7373. Aording to D6731/ 2011, Bio-degradation of alubriant, or the omponent of a lubriant, is determined by measuring the oxygen on-sumed when the lubriant or omponent is exposed to miroorganisms under ontrolledaerobi aquati onditions. [8?. LC50 & LD50 are the lethal onentrations or dosesthat ause death to 50 % of the tested animals group [9?. The animals are usually ratsand mie, whih an be exposed to the lubriant by skin exposure, an oral dose, or in-halation. This is deided based on the intended appliation and hosen medium, whihould be via air, water, or diret exposure. The dose is alulated with respet to theanimal's weight and the onentration by ppm.71.7. Canola Oil in Canada's EonomyRegardless of the environmental impat, mineral oil omes from a limited soure,petrol. The onrmed and potential preserves are still under debate, but most souressay the pries will go up before we ome to the end of the supply. This makes ompet-itive tehnologies more feasible. The vegetable oils an not only deal with most of theonerns that have been mentioned above, but also satisfy most expetations regardingthe performane of a modern lubriant. One of the main hallenges with bio-lubriantsis oxidation, so most bio-lubriants are being used for appliations that do not requirehigh temperatures. There are some suessful attempts to modify bio-oils into morestable oils and use them in harsh onditions like those from internal ombustion engines.[6? However, in terms of the limited supply, it is still more eonomially feasible to usethem in appliations with temperatures of less that 100oC.1.7 Canola Oil in Canada's EonomyCanola oil is one of the vegetable oils that have been used ommerially as a lubriantbase for many appliations. It is genetially improved from rapeseed and has the po-tential to be modied more to suit spei requirements. Seed oils and their produtsrepresent the largest rop trade in the world. While rapeseed prodution in Canadastarted in 1936, it beame more widespread in 1942, in an eort to provide new souresfor lubriants to war mahines. Furthermore, the rst genetially modied low Eruirapeseed oil was produed in Canada 1968. The name Canola was adopted in 1978 todenote double-low Erui aid rapeseed. These onseutive suesses led Canada to bethe largest exporter of rapeseed in the world [10?.Nowadays, the anola industry ontributes $15.4 billion annually to Canada's eon-omy, and provides 228,000 jobs. Canada produed 9.0 million Tonnes of anola produtsduring 2006, whih reresents about 15% of global prodution and 75% of its trade. Only81.8. Physial and Chemial Properties of Canola OilFigure 1.4: Utilizations of anola oil20 to 25 % of Canadian prodution goes to Canadians onsumers. That represents 40%of the loal vegetable oils market. Regardless of the saturation level of the domestiCanadian market, the edible market, even with the remaining 60%, does not satisfy theimpetus plan that targets 15 million tons in 2015. It is obvious that exporting wouldsustain the development of the anola industry. In addition, diversifying the uses ofappliations for rapeseed oils would inrease the stability of this industry. As a matterof fat, a signiant portion of the future inrease will be attributable to the bio-fuelsetor [11?. The grease and lubriants industry, besides, ould be promising onsumersof anola oil.1.8 Physial and Chemial Properties of Canola OilCanola oil omes from rushing the Brassia Seeds that belong to the mustard family.Aording to the anola ounil of Canada, anola oil is: an oil that must ontain lessthan 2% Erui aid, and the solid omponent of the seed must ontain less than 30 miromoles of any one or any mixture of 3-butenyl gluosinolate, 4-pentenyl gluosinolate, 2-hydroxy-3 butenyl gluosinolate, and 2-hydroxy- 4-pentenyl gluosinolate per gram of91.9. Additivesair-dry, oil-free solid [11?. As with most vegetable oils, anola oil is mainly a triglyerideof fatty aid hains. Fig (1.5) shows the moleular struture of the triglyeride, glyerolportion and olei aid. The last one represents more than 60% of the fatty aids in anolaoil; (see table 1.1) [12?. Table 1.2 gives the Triaylglyerol omposition of anola oil [13?.The hemial omposition is responsible for the thermal and oxidation properties of theoil [13, 14?.Figure 1.5: Moleular Struture of the main ompositions in anola oil [14, 15?Compared with mineral oils, anola oil has highly polar and larger moleules [18?; ithas very good lubriity and a high visosity index (VI); it has less volatility and a higherash point; it has better detergent and anti- orrosion properties. On the other hand,anola oil has higher pour point and lower oxidation stability. Some physial propertiesof tested oils, suh as density, thermal expansion, and surfae tension, were measuredand reported in the appendix.1.9 AdditivesThe perentage of additives in a lubriant an be up to 30% [6?, while the additives intested oils varies from 5 to 10% [1?. Lubriation tasks exeed merely dereasing fritionand wear; they involve suh jobs as dissipating heat, onduting or insulating eletriity,101.9. AdditivesTable 1.1: Chemial omposition of anola oilFatty aid symbol Formula Wt (%) No. of CPalmiti P CH3(CH2)14COOH 3.68 16Olei O CH3(CH2)7CH CH(CH2)7COOH 63.49 18Linolei Li CH3(CH2)4CH CHCH2CH CH(CH2)7COOH 20.05 18Linoleni Le CH3CH2CH CHCH2CH CHCH2CH CH(CH2)7COOH 9.46 18Steari S CH3(CH2)16COOH 1.65 18Eiosenoi - CH3(CH2)7CH =CH(CH2)9COOH 1.16 20Arahidi - CH3(CH2)18COOH 0.51 20Erui - CH3(CH2)7CH= CH(CH2)11COOH <0.1 22Table 1.2: Triaylglyerol omposition of anola oilTriaylglyerol POP PLiP POO POLi POLe PLiLe TOTALMole frations 0.009 0.0057 0.0909 0.0668 0.039 0.0105 0.9999Triaylglyerol SOO OOO OOLi OOLe OLiLe OLeLe TOTALMole frations 0.0214 0.23276 0.2409 0.1776 0.0756 0.0249 0.9999removing foreign partiles, and keeping them out. Usually, the base oil lubriant annotsatisfy all of these requirements. Thus, dierent pakages of hemial additives are addedto enhane the lubriant's funtionality. While many of the additives are responsible fora signiant part of the superior performane of modern lubriants, some of them, likeheavy metals and polymers, aount for the toxiity and biodegradability resistane [18?.Some indiators and tehniques are used to measure and evaluate the performane of alubriant, suh as : Visosity index (IV), IOS number, pour point, ash point, and seizurepoint. The additives inlude anti-oxidants, orrosion inhibitors, anti-foam agents, anti-wear agents, visosity modiers, visosity index improvers, detergents, and dispersants.As for visosity, anti-wear agents, detergents, and dispersants, the natural propertiesof some bio-oils are good enough to work even without any additives. Moreover, theonventional additives would be not ompatible with bio-oils, whih means they wouldnot be hosen for use with environmentally friendly bio-lubriants. A low amount ofphosphate and phosphate esters an be used to enhane the degeneray; sulphanatesmake good orrosion inhibitors; an amine phosphate ompound is good for as antiwear,111.10. Lubriation Regimesand silion is a good anti-foam agent [18?.In our study, the additives in the lubriants are ondential information that isnot intended to be revealed. However, no visosity improvers were added and we maygenerally assume that the bio-lubriant behaviours are mainly inherited from the originalhemial omposition of the anola oil.1.10 Lubriation RegimesWhile Stribek's urve (1902) explained the frition in journal bearings, it still insistson the main onept of the transition from one lubriation regime to another. The twomain ategories of lubriation regimes are hydrodynami and boundary lubriation. Inhydrodynami lubriation, both sliding surfaes are separated ompletely by layer of uidwith more than 1mm of thikness [19?. The frition in this regime is very low, whih isonly due to the visosity, so visosity is the most vital property in this regime, besides thenature of the ow. On the other hand, we have the boundary regime, in whih the slidingsurfaes are muh loser to eah other, 1 to 10 nm. This narrow spae is oupied bysingular or multi-moleular layers . Thus, the visosity does not beome as important asin the previous regime. Instead, other physial and hemial properties of the oil, whihaet how it reats with metal surfaes, beome more important. More details aboutthe surfatant properties of the oil will be disussed later. Some other regimes ouldbe lassied in between boundary and hydrodynami, suh as elasto-hydrodynami, inwhih elasti deformation beomes signiant, whih takes plae between Non-onformalsurfaes. The onformal surfaes t eah other so the engaged area keeps onstant, asin a journal bearing. Nononformal onjuntion is like mating gear teeth [19?. Anotherregime that an be mentioned is the mixed regime, in whih the hydrodynami regimeis mixed with the boundary regime. Figure (1.6), Stribek's urve, plots the relation121.10. Lubriation Regimesbetween frition oeient and dimensionless Hersey number that is given as [19?:Hs =??p (1.1)where ? is the dynami visosity, ? is the rotational speed, and p is the pressure.Figure 1.6: Stribek's urveFrom a pratial point of view, a good lubriant is designed to deal with all regimesbeause, not only it is diult to nd a mahine with one regime of lubriation, but therubbing oupling itself an transit from one ategory to another. Figure 1.7 shows energylosses in the internal ombustion engine [20?, where the losses are due to dierent kindof regimes. In journal bearing, whih shows a lear ase of the hydrodynami regime,the lubriation beomes mixed at low speeds.131.11. Surfatant BehaviourFigure 1.7: Energy losses in the internal ombustion engine1.11 Surfatant BehaviourEven during boundary lubriation, where the pressure is very high and the surfaes arevery lose to eah other, there is still a layer of single or multi- moleules in thiknessseparating whih dereases the wear and frition signiantly.Figure 1.8: Adsorption mehanisms in fatty aids on steel surfaesThe moleular self-assembly depends on the material nature of the lubriant andrubbing surfaes. There are dierent mehanisms by whih these lms an format, aslisted in referene [21?, and as follows: 1- physial adsorption; 2- hemial adsorption;141.12. Liquid Crystals [2, 22?3-hemial reation not involving substrate; 4- adsorption; 5-hemial reation involvingsubtrate. Referene [17? further more elaborates on physial adsorption, whih inludesapillary, eletro-stati, and Van der Waals fores. Inreasing the stability and thiknessof the self-assembled layer will reet positively on the lubriat's performane. Besidesinfrared and X-ray spetrosopy, there are many tools that an be used to study thisphenomenon, suh as probe mirosopy, whih inludes atomi fore mirosopy, a fri-tion fore mirosope, a hemial fore mirosope, an interfaial fore mirosope, anda surfae fore apparatus,. Fig 1.8 shows the adsorption mehanism of fatty aids onto steel surfaes [21?. While new advaned tehnology revealed muh about previouslyunexplained phenomenon, we still have a long way to go. There is still diulty bothin explaining the tribologial behaviour, and in mathing between its mirosopi andmarosopi aspets [17?. In this researh, the rheometer will be represented as a newtool to be used to haraterize the surfatant behaviour of the lubriant.1.12 Liquid Crystals [2, 22?Liquid Crystals (LCs) are anisotropi, visoelasti materials with that ombine a uid-like with rystal-like properties. Liquid rystal material an improve the lubriity ofa lubriant, and while it is not yet fully understood how they work, there are someexplanations available, due to the orientation and the surfae ativities. With respet todierent ow diretions, the anisotropy of the visosity oeient, is a unique propertyof the liquid rystalline phase. The ability of liquid rystalline materials to form orderedboundary layers with good load-arrying apaity, while lowering the frition oeients,wear rates, and ontat temperatures of sliding surfaes.[2?The rod, nemati liquid rystals onsist of ylindrial moleules more or less aligned ina ommon diretion, represented by the uniaxial diretor n . Some materials ould have151.12. Liquid Crystals [2, 22?more than one phase of liquid rystals, aording to temperature and/or onentration.The liquid rystals an have order in position and orientation; whih is alled smeti.Fig (1.9) illustrates both the smeti and nemati phases.Figure 1.9: Nemati and smeti order of liquid rystalline phases16Chapter 2Methodology2.1 Literature Review2.1.1 Rheometry of Bio-lubriants and Low Visous MaterialsThe researh regarding lubriation problems has foused mainly on experimental workon the oil's tribologial performane, and the CFD modeling of hydrodynami fritionthat implemented visoelastiity. Meanwhile, applying rheometery dynami tests on oilshas been limited. Rotary rheometers have been used more ommonly to test the oils atmoderate shear rates. Both apillary rheometres and falling ball visometers have beenused to study high shear and high pressure, respetively. Considering the problem oflubriation generally, the studies that addressed the visoelastiity in lubriants fousedmore on greases and emulsions.2.1.1.1 Rheometry of Bio-oilsThe bio-hydrauli oil that was tested in this researh, however, was studied before rhe-ologially [23?. Some vegetable oils, inluding anola oil, showed strong shear thinningat a shear rate of 100 s?1 and lower [24?. Inexpliably, the shear thinning inreasedwith temperature, whih questions the stability of the experiments. While the previousresearh used visometer, we used an advaned rheometer, about whih the manufa-turer says it has the lowest inertia motor in the market. However, it beame diultto maintain stability at a very low visosity. Other studies foused on the orrelation172.1. Literature Reviewbetween the fatty aids omposition of the bio-oils and their visosities, within a tem-perature range from 20 to 100oC [13, 25, 26?. While the studies [13, 26? used apillaryvisometers, a rotating visometer was used in [25?. It was found that the visositiesof pure saturated triglyerides follow the seond order funtion of the arbon numberquite well. The behavior of dierent vegetable oils at low temperatures, i.e., of up to-40?C, was studied using a rotational ontrolled strain rheometer [27?. The uidity wasremarkably improved by using visosity modiers, where the pure point dereased from-18 to  36?C. While the pressure dereases the density and inreases the visosity, pres-surized orn oil, using ompressed CO2, showed the opposite, due to the dissolution ofCO2. The tested pressure went up to 12 MPa in a pressure ell ombined with a rotaryrheometer [28?. A mixture of soybean and ommerial oils was optimized using a rotaryrheometer to ahieve the desirable visosity index (VI) [29?.2.1.1.2 Rheometry of Low Visous LiquidsDue to the low torque and instability assoiated with low visosity, the pratie of usingrotary rheometers to ondut dynami tests in the eld of lubriants is done almost ex-lusively on greases, emulsions, and gels that have higher visosities [30, 31, 32?. Whilethese limitations an be extended to low visous materials generally, some eort hasnonetheless been made to try and do further testing. The results of a frequeny sweeptest of lubriant alled peruoropolyether are represented in referene [33?. The peru-oropolyether lubriant had a visosity of 0.08 Pas at 10?C. The lubriant did not shownon-Newtonian behavior at a shearing rate less than 103 s?1. Further, G' was inverselyproportional with temperature, between 10 and 30?C and almost onstant between 30and 50?C. The frequeny domain was between 0.04 and 4 Hz. To our knowledge, thematerial with the lowest visosity, whih had been tested under SAOS using the rotaryrheometer, was holesteri liquid rystals, [34?. The visosity was about 0.04 Pas, whih182.1. Literature Reviewis equivalent to tested oils in this researh at 40?C.2.1.1.3 Rheometry of More Visous Related MaterialsRegarding more visous materials, heavy oil, 2 Pas at 80?C, was tested under a widerange of frequeny, i.e., 0.01 to 100 Hz [35?. Crystalization in the formulation of palmitifatty aid was studied using a frequeny time sweep [36?. Palmiti fatty aid is one ofthe omposite omponents of anola oil. The waxy appearane in rude and paran oilswas investigated using visometry tests [37, 38?.2.1.1.4 Rheometry of Engine OilsMore intensive work has been foused on engine oil, espeially at high pressure andshear rates. A fall objet visometer was used to study the eet of pressure up to1.2 GPa [39, 40?. Oil visosity responded to extreme pressure more than exponentiallyinreasing. Using a apillary tube, at 38?C, poly alpha olen showed shear thinning atthe high shear rate of 103to 107 [39?. There was no regaining of the plateus at the end ofthe urve. It is worth mentioning that slipping ould take plae at a high shear rate. Theother study, whih used the apillary tube rheometer, found that pressure has a stronginuene on the visoelasti properties of multi-grade oils [41?. The work done at Shell'sresearh enter on multi-grade oil 10W50 showed shear thinning between two plateauregimes. The shear thinning appeared earlier as the temperature dereased [42?. Thepositive visoelastiity impat on the performane of multi grade oil was demonstratedusing rheometery and tribology simulation [43?. The veloity eld of multi-grade oilwithin an eentri ylinder was determined using a Doppler laser gauge. This uniqueeort aimed to validate upper-onveted Maxwell model in visoelasti lubriation [44?.192.1. Literature Review2.1.2 Rheometry ErrorsSome of the measuring errors when rotary rheometer is used are more assoiated withlow-visous liquids rather than thik and strong materials. The most ommon are: thegap errors at very small gaps, liquid inertia ontribution, seondary ow due to the widegap or misalignment, and unsteady rheometer. Further, the low visous sample ould beaeted by heat dissipation and wall-slip to a lesser extent. Thus, studying these errorsand quantifying them has been drawing many researhers' attention. In eort to ahievevery high shear rate within a thin gap, the gap errors were studied extensively in parallelplate geometry. The errors in gap size were attributed to misalignment of the parallelplates, and ontribution of the air pressure during the squeezing for gap zeroing, [45, 46?the liquids' inertia eets within onentri ylinders and wide gap were studied [47, 48?.The ontribution of the liquid inertia to storage modulus in parallel plate and onentriylinders measuring systems was quantied also [49?. Non-parallelism in parallel platemeasuring system was studied theoretially in ase of Newtonian uid [50?. The unsteadyrheometery whih has signiant impat on dynami tests was studied theoretiallyand experimentally [51, 52? It was found that time response of the rheometer inreaseswith inertia and dereases with the sample visosity, also the maximum frequeny wasdetermined based on the oupling between the rheometer and the sample. Wall-slip wasmeasured experimentally, and it was found that it was important as it ould aet theCFD simulations aording to dened boundary onditions signiantly [53?2.1.3 Mathematial ModelMathematial work on lubriation has been fousing on the hydrodynami lubriationwith more emphasize on the ow within eentri ylinders and journal bearings. Aremarkable number of researhes modeled lubriants as non- Newtonian uids and withmuh less as visoelasti lubriants. D. Greov simulated the non-Newtonian ow within202.1. Literature Revieweentri ylinders using stream-tube method [54?. T.N. Phillips published number ofpapers to simulate the ow within dynamially loaded journal bearings using Oldroyd-Band PTT models [55?. H. Bouherit after he studied dierent forms of the Maxwellmodels onluded that there is still a gap between visoelasti mathematial modelsand experimental data for real lubriation ases [56?. This questions the redibilityof applying the known visoelasti models on the ow of lubriant within a journalbearing. There is a few works in that aspet, referene [44? is one of them. Eventhough the validation of Maxwell model was proved aording to that researh, still theinvestigated ase was ow within eentri ylinders rather than real ase of journalbearing. Meanwhile, there is a new eort to use the moleular dynami to simulate verynarrow gaps [57?.2.1.4 Thermal AnalysisThe Dierential Sanning Calorimetry (DSC) tehnique has been used widely to studybio-oils for dierent purposes. It was suessfully used to study the waxy appearanein vegetable oils, where two peaks on the DSC urve were identied at low tempera-tures; these were attributed to the oil's moleular struture and two dierent forms ofrystalline phases [58?. DSC studies on dierent vegetable oils have also revealed a on-netion between their thermal behavior and hemial ompositions [59, 60?. DSC wasused, as well, to investigate and improve the oxidation stability of dierent vegetablesoils, suh as soybean, saower, sunower, and mustard oil [61, 62?, and to diagnose sed-imentation in anola oil [63?. Other researh found a onnetion between rheology andDSC, where transition points appeared on the urves of shear visosity, storage modulus,and heat [64, 65?.212.1. Literature Review2.1.5 Bio-lubriants TribologyIt is well known that vegetable oils have good lubriity, due to their triaylglyerolstruture. A study on Palm oil showed that it has a lower spei wear rate omparedwith ommerial mineral oil [66?. In ontrast, oonut oil has a larger wear rate omparedwith ommerial oil, as shown in an extreme pressure test [67?. It should be taken intoonsideration that most of the researhes on vegetable oil used just raw oils, whereasthe ommerial oils are enhaned with many improving pakages. These improvingpakages ame as a onsequene of the long umulative experiene of giant ompaniesthat speialized in the eld of lubriants. The performane of saturated steari aidand unsaturated linolei aid as additives to improve lubriity was studied [68?. Theexperiments were done on both the nano and miro sales. While the mehanism of howthese materials adhere to steal and form self-assembly monolayers is dened, it is stillnot lear why it is time dependent.2.1.6 Liquid Crystal AdditivesWhile many researhers have been studying the tribologial eet of liquid rystals onoils, they were mainly on mineral oils; far fewer have been done on bio-oils.2.1.6.1 Liquid Crystals with WaterAlkyl polygluosides, were tested as an additive to water [69?. The tribologial experi-ments showed a redution in frition of up to 7 times. Additionally, several other testswere onduted, inluding: surfae tension, wetting angle, light diusion and visos-ity, atomi fore mirosopy, polarized light mirosopy, and X-ray spetrosopy, whihindiates the existene of mielles and liquid-rystalline strutures.222.1. Literature Review2.1.6.2 Liquid Crystals with Mineral OilsA study on six types of holesterial liquid-rystals with four mineral oils [70?, foundimprovements in wear redution over all of them. Also, it gave a hemial explanationto the deformation of the monolayer and the advantage of holesteryl hloride over theothers, due to its hlorine ontent. Another researher [71? studied 14 additive materialsfrom dierent families of liquid rystals. They were tested with dierent oil bases onrubbing ouple of steelsteel, and the results were positive for all of them, over all testedtemperatures (from 27 to 50oC). Also, they found that the hange in visosity hadlittle eet on the results. In an attempt to ahieve ultra-low frition, a mesogeni uidmixture was used [72?. Comparing the tribologial performane of ioni and neutralliquid rystal additives, all experiments showed that ioni liquid rystals have less wear[73?. In a related eort, 7 dierent ioni liquid rystals were tested [74?. One of themwas 1-butyl-3-methylpyridinium with an oil base and Aluminum-steel ontat oupling.They showed positive improvement, whih the researhers attributed to the eetivelyadsorbed lubriating layers due to the reation between the steel and ioni liquid rystal.2.1.6.3 Liquid Crystal with Bio-oilsThere is limited number of researhes that deal with liquid rystals as additives tobio-lubriants. 5% of bori aid was used with anola oil and resulted in a superiorlubriant, even over ommerial lubriants [75?. The relative improvement with pureanola oil itself was not mentioned. The impat of ioni liquid rystals on dierent oils,inluding bio-oils, was investigated [76?. The very low frition oeient indiates thatthe frition is either hydrodynami or mixed. It is known that the visosity is veryimportant in these regimes, where the tested samples have wide variations in visosity.Moreover, there is a signiant ontrast in the results among anola oil, saower oil,and vegetable oil, espeially the fat that anola and saower oil have similar hemial232.2. Materialsompositions.2.2 MaterialsFigure 2.1: Greenland oilsGreenland Corporation is a Canadian ompany loated in Calgary, Canada. Theymanufature bio-lubriants from anola oil. They have 14 dierent produts. In thisresearh, three of their produts were tested: hydrauli oil, gear oil, and hainsaw oil. Aswell, a ommerial mineral hydrauli oil was tested, as shown in gure (2.1). With thegoal to ompare these oils during the period of the study, only two bathes of these oilswere tested and no hange was notied. Neither the onsisteny of lubriants nor theirhemial omposition was investigated. The ompany says it has restrit quality ontrolon the raw materials, although they are still biomaterials and some variations are notvery far from. In addition, two types of liquid rystals from Sigma Aldrih were usedas additives: 97% holesteryl hloride, 1-butyl-3-methylimidazolium (tetrauoroborate).The moleular strutures of both liquid rystals are illustrated in gure (2.2). Silionoil, in ompliane with United Kingdom standards, was used as a alibration oil to hekthe auray of the rheometer, periodially. (See gure (2.3))242.3. Rotary RheometerFigure 2.2: Liquid rystals additivesFigure 2.3: Calibrating oil2.3 Rotary RheometerThe rotary rheometer is often used, due to its advantages: it requires only a small samplesize; it is easy to apply ertain onditions on the sample suh as temperature, eletrield, and UV exposition; it works ontinuously, so it an run as long as the nature of thesample allows. While researhers an lassify rotary rheometers based on its ontrollingmodes, i.e., rate ontrol or stress ontrol, these are not suh a distinguishing feature, asmany modern rheometers an work in both modes. It is more pertinent to lassify rotaryrheometers based on their torque sensor loations. While on single head rheometers, thetorque sensor and the motor are loated in one side, in the separated heads rheometer,they are separated by the sample. While the rst setup is simpler and more exible252.3. Rotary RheometerFigure 2.4: Illustrative shemati diagram of single head design of a rotary rheometerfor applying dierent environment ontrol failities, it has to deal with motor inertiaand bearing noise, whih aet its auray. Figure (2.4) provides a general illustrativesheme of the single head design.The rheometer used in most rheometery experiments in the urrent researh was theKinexus brand, manufatured by the Malvern ompany as is shown in gure (2-5). Ithas dual ontrolling mode apabilities for both shear and stress, it is a single head, andprovided with porous air-bearing.The two major sensors in the rheometer are the position and torque sensors. Theposition sensor was not a onern for us. For example, assume we are applying a shearrate of 10?2 , using a one and plate of 20 mm radius / 1o angle, the angular veloityunder these severe onditions would be around 2.7 X 10?5 rad/s, while the enoder in theKinexus rheometer has a resolution of less than 10?8 rad/s. The hallenge was measuring262.3. Rotary RheometerFigure 2.5: Kinexus rheometerthe torque. Even though the rheometer we used has a highly sensitive sensor, namely 5 X10?8 Nm, it has to deal with the noise oming from the inertia and porous air-bearing. Inthe ase of a highly sensitive sensor, the auray is limited to unpredited noise ratherthan the auray of the torque sensor. In this respet, the software, whih has to dealwith the orretions as well as the preise ontrols, espeially in dynami tests, is justas important as the hardware, maybe more. Not all the information about the softwarewas available to us. The lowest torque onsidered in the reported results was 10?6 Nm.The rheometer we used did not measure the gap diretly as the most rheometers on themarket, generally. Instead, it is the displaement of the motor that is measured, andthe zero gap is reognized by the normal fore. Even the very sensitive displaementsensor, 10?7 m, annot guarantee error-free gap measurements at small gaps. It is worthmentioning that, while gap error due to inaurate gap size an hange the values,behavior of the oil remains onsistent. Meanwhile, errors due to the imperfet shape ofthe geometry or non parallel ould also ause hanges in the oil's behavior, beause of theseondary ow. The motor inertia of the Kinexus rheometer is 13?N.m.s, whih is thesmallest inertia of any rheometer motor on the market, aording to the manufaturer.272.4. Measuring SystemsFurther, the maximum torque laimed is 200 mNm. In pratie, it ould be above orlower than this, depending on the rotation speed. We also notied that the rheometerhas high and stable aeleration ompared with other brands. However, we do not havea omplete understanding of the rheometer's dynami response, but we relied on somemeasurements provided by the software, whih will be disussed later in this hapter.2.4 Measuring SystemsDierent measuring systems an be used by the rotational rheometer, based on theproperties of the materials and the purpose of the test. It is desirable that the resultis independent of the geometry, whih is not always the ase. The one and plate, on-entri ylinder, and parallel plate measuring systems are desribed by ISO 3219(1993),6721-10(1999) [77?. The advantage of these geometries is that the applied shear is de-ned aross the sample. However, the shear is onstant only in the one and plate, andin the onentri ylinder. The varying shear rate with diameter in at plate measuringsystems adds omplexity to the alulations when the visosity is shear dependant. A-tually, we used at plate geometry in most of the experiments beause of the ability toontrol gap size. Figure (2.6) is a shemati drawing for the at plate system.Figure 2.6: Parallel plate measuring system282.4. Measuring SystemsThe upper disk is moving while the lower is xed. Both shear rate and shear stressare required to alulate the apparent visosity (Eq. 2-1). The shear rate varies linearlyfrom zero at the enter to maximum at the rim of the plate, whih is determined by thefollowing equation:? = ??o (2.1)?oR =R?h (2.2)Where ? is the visosity , ? is the shear stress, ?o is the shear rate,?oR is the shearrate at the rim of the geometry, R is the radius of the geometry, and h is the gap size, ?is the angular veloity. In the following, the shear stress is a funtion of the radius. Theshear stress on the rim an be obtained from the integration over the radius[45, 78?:?R =M2piR3 (3 +dln(M)dln(?oR)) (2.3)Where M is the measured torque. To solve the above equation, the relation betweenM and ?oR. needs to be determined rst, whih means adding orretions to the results,unless the tested material is a Newtonian uid. In many ases, when the tested materialexhibits shear thinning or thikening, it an be approximated to power-law. Aordingly,in the ase of a Newtonian uid and power-low material, Eq. (2.4) an be used toalulate the visosity [45, 78?:? = 3Mh2piR4?(1 +n3 ) (2.4)Where n is the power-law onstant, whih is one, in the ase of a Newtonian uid.It should be pointed out that the rheometer software alulates the visosity based on292.5. Short Amplitude Osillation Shear (SAOS)the Newtonian equation, and onsiders the shear rate at 0.75 of the radius.2.5 Short Amplitude Osillation Shear (SAOS)Just as Newtonian uid obeys Newton's laws, Hookean solids obey Hooke's laws. Thisimplies that Hookean solid is linear elasti. Some materials, whih are alled visoelasti,have the ability to dissipate energy as Newtonian uid and store it as a Hookean solid.The SAOS test an demonstrate the two omponents of the tested material.Figure 2.7: Time dependant funtions of SAOS, (shear rate, strain and stress )Considering applying an osillatory shear to the sample instead of a ontinuous shear,aording to the following equation [77, 78, 79, 80?:?(t) = ?Asin(?t) (2.5)Where ?A is the shear amplitude, ? is angular frequeny, and t is the time. Conse-quently, the shear rate preedes the shear strain by (p/2) or follows a osine funtion, asis shown in gure (2.7). The response of the sample or shear stress depends on the prop-erties of the material being tested. If the sheared material was an ideal elasti solid, the302.6. Mathematial Model [80?shear stress would be in phase with the strain. If the sheared material was ideal visousuid, the shear stress would be in phase with the shear rate. The visoelasti materialresponses fell somewhere in between with phase angle ( d ), whih is between zero and (p/2). Besides the phase angle, the measured torque or alulated shear stress amplitudeimply two important measurements; the storage modulus (G'), whih is a measure ofthe elasti part; and the loss modulus (G), whih is a measure of the visous part. In asimilar way, the ontrol mode ould be based on shear stress and the measured propertyis the strain amplitude and plus the phase angle.G? = ?A?A(2.6)G? = ?A?Asin(?) (2.7)G?? = ?A?Acos(?) (2.8)Where G? is the omplex modulus. The previous measurements an be expressed inomplex numbers notations, as follows:G? = G? + iG?? (2.9)2.6 Mathematial Model [80?The Newtonian uid onstitutive equation is expressed as follows:=? = ?=?o (2.10)312.6. Mathematial Model [80?=?o = ?v? + (?v?)T (2.11)=? =???????xx ?xy ?xz?yx ?yy ?yz?zx ?zy ?zz??????(2.12)Where=? is the stress tensor,=?o is the rate of strain tensor , and ??v is veloity gradienttensor. For non-Newtonian uids, the visosity is a funtion of the shear rate, so theonstitutive equation an be generalized as follows:=? = ?(?o)=?o (2.13)The funtion h(g?) whih ould be `power-law' an represent a non-Newtonian uidaurately only when the eet of the shear history or the memory is negleted. In aseof visoelasti materials, it is valid only when the ow is steady and time independent.The Maxwell model inorporates the memory eet by inluding the time derivative ofthe shear stress.=? + ??=??t ? ?o=?o = 0 (2.14)[Maxwell model, integral form?=? (t) = ?? t??[?o? e?(t?t?)? ]=?o(t?)dt? (2.15)Where ? is the relaxation time of the material, ?o is zero shear visosity, t is time ofinterest, and t? is a dummy veriable denotes the past times. The model was built onthe basis of its resemblane to the mehanial model, spring dashpot as is illustrated in322.6. Mathematial Model [80?gure (2.8)Figure 2.8: Visoelasti material is resembled to mehanial model of spring and dash-pot in seriesWhile the spring represents the elasti part, whih has the ability to store energyand exert resistane to deformation proportional with the strain amplitude, the dashpotrepresents the visous part, whih dissipates energy and resists deformation proportionalto the strain rate. Applying Maxwell model on the SAOS, whih is the simple shearrate, gives:=? (t) = ?? t??[?o? e?(t?t?)? ]??????0 ?oA cos(?t?) 0?oA cos(?t?) 0 00 0 0??????dt? (2.16)G??(?) = g??1 + ?2?2 (2.17)G?(?) = g?2?21 + ?2?2 (2.18)332.7. Unertainty2.7 UnertaintyWith low visous and low visoelasti materials, trivial errors an beome signiant.Thus, we paid arful attention to insure a high level of auray, whih meant we hadto take a number of approahes:1. We were areful that all the experiments onditions fell within the rheometer realapabilities, whih are: maximum torque at high rotation speed; lower torqueat a low angular speed; maximum rotation speed; maximum stable frequeny,aeleration time; and the lowest temperature at a high shear rate. However, wedid not need to exeed all of these limitations in most ases, exept the low torqueand high frequeny, whih were always a hallenge we had to overome2. The most ommon errors have harateristi signatures on the results. Observingany of these patterns is a prompt to investigate for errors.3. In the ase of the omparison between the bio-lubriant and Silion oil and engineoil, where the rst one is onsidered a Newtonian uid, the seond one is onsideredas a dilute polymer solution. We think the omparable visoelastiity is moremeaningful than the numbers themselves.4. The rheometer software has many measurements that alarm some types of errors.The most important three of these warnings will be detailed.2.7.1 Software Error Measurements [81?2.7.1.1 Steady StateSteadt state indiates the equilibrium, whih is determined by two dierent equations,depending on the ontrol mode. It should stay around ( 1.0 ) regardless of the appliedequation or ontrol mode. The test time ould be deided automatially based on the342.7. Unertaintysteady state, but it was set manually in most of the experiments we reported. Meanwhile,we were areful to make it long enough to preserve an aeptable steady state. Theequations that determine the steady state are:SSCS =dln?(t)dln(t) ?dln(?)dln(t) (2.19)SSCr = 1?dMdt ?tits(2.20)where SSCS is steady state measurment in ontrolled stress mode,SSCR is steadystate measurmnet in ontrolled rate mode, ti is integration time, and ts is sample time.2.7.1.2 Harmoni DistortionThis is the measurement of how the input and output signals in SAOS are sine funtionsalike. The harmoni distortion was lower than 5% in all of the reported results.2.7.1.3 Inertial Eets DominatingThis warning appears when the phase angle is lose to 90o, and the elasti ontributionis too small to be aurately onsidered.2.7.2 Gap AurayThe displaement sensor does not measure the gap diretly, but measures the headmovement instead. Thus, some gap errors are expeted, whih beome more signiantat the very small gaps. Assuming the gap error is onstant, whih is not always the ase,it an be extrated from the following equation [45?:? = ?mhmhm + ?g(2.21)352.7. Unertaintywhere ?mis the measured visosity, hmis the measured gap, and ?gis the gap error.Figure (2.9) shows the measured and orreted visosity of bio-hydrauli oil. Aordingly,the error in the visosity varies from 2.3 to 3.5 % at gaps 0.3 and 0.4 mm, respetively,whih were the most used ones.Figure 2.9: Visosity orretion due to the gap error, bio-hydrauli oil at 20?C2.7.3 Auray Versus Shear RateIn an eort to investigate shear thinning or thikening, the visosity of the oils tested wasmeasured against the shear rate, as will be presented in (Chapter 3). For the purposesof validation, the same experiment setup was applied to the silion oil, standard oil,as shown in gure (5.10). The errors in the average visosity at 30?C were less than 1%. Slight shear thinning ould be observed, even in the silion oil ase beause of theseondary ow. In a omparison, this level of hange in visosity of the tested oil willnot be onsidered.362.7. UnertaintyFigure 2.10: Visosity versus shear rate, standard oil2.7.4 RepeatabilityThe rheometer software is still being evolved by the manufaturer, and the rheometerwas used by dierent researhers. Thus, the auray of the gap was heked period-ially, using the tested oil itself, and the measured visosity was heked periodiallyusing standard oil, espeially before the visometery experiments. Aording to the ex-periments done on standard oil, we assume the error of measured visosities to be within2%. The tolerane in the measured visosity at the same temperature and shear rate isnot more than 1%. The soure of any non-repeatability most probably ame from howthe sample was trimmed or how the sample lled the gap, sine it is a manual proess.Where the G' depends on the deliate mirostruture of the bio-oils, the repeatabilityin the SAOS tests was more onerning. As it will be presented, however, the reportedresults were estimated to be stable by 95%. Six dierent experiments at three dierentgaps gave a variane from 2.3 to 16.5%.37Chapter 3Rheologial Charaterization3.1 OverviewThe best experimental onditions are the losest ones to real ase, whih is not alwayspossible. Designing a good rheology experiment requires a solid knowledge about theonerned material, working onditions, and testing equipment. Our knowledge aboutthe materials and the equipment has been developing in time for two reasons. A similarstudy on the same type of the materials was not available, espeially with this extend.Estimating the real apabilities of rheometer is more than onsidering the named spei-ations, whih are not detailed to over every senario, speially. Consequentially, thereported experiments are the nal version of our developing experiene. Generally, therheologial experiments presented here an be lassied into main ategories; the moreommonly used ones are: the visometry and the SAOS tests. As well, the followingomplex proedures and spei purpose experiments were designed to answer speiquestions:? The visometery experiments inlude testing the single shear rate at dierent tem-peratures, and the rising shear rate at onstant temperatures.? The SAOS experiments inlude shear amplitude sweeps and frequeny sweeps atdierent temperatures. Only the results that were estimated to have reahed astability state with a reasonably low sattering will be presented.? The omplex proedures onsisted of sequential experiments, for instane, dierent383.2. Visometerypatterns of shear rates at dierent amplitudes of osillation time sweep tests, andombinations of the two. These tests were used to investigate time dependent andstruture reovery.? Speial experiments were designed for ertain purposes that ombined using highpressure, polarized light mirosopy, dierent gap sizes, and dierent geometrymaterials.3.2 Visometery3.2.1 Visosity Versus TemperatureThe tested bio-lubriants in the present study do not ontain any visosity improvers.The investigated temperature domain varies from 0 to 100oC besides being a reasonablerange from a pratial aspet; it is also a stable range for the rheometer temperatureontrol. The same sample was tested at dierent temperatures, from 0 to 100oC, everytime. It was given 5 minutes to stabilize under the aimed temperature, and it wassheared at onstant shear rate (10 /s). The hysteresis eet due to the temperaturehange was negleted, as it was not thought to be signiant. Figure (3.1) summarizesthe results of three bio-lubriants and ommerial mineral hydrauli oil tests. In termsof thermal stability, all of the bio lubriants have advantages over ommerial mineralhydrauli oil. Both the bio- hydrauli and bio-gear oils followed similar patterns andhave lose visosity along the tested domain, whereas the bio-hain saw oil deviates fromthem at temperatures lower than 20 C. It was noted that one exponential equation ouldnot interpolate the visosity aross the entire temperature range, aurately. The samebehavior appears in other researhers' results of anola and other vegetable oils [13, 26?without mentioning it expliitly. The same behavior was also found in other work onrude oil. This was attributed to the wax appearane around 45?C [37?. Similarly, all393.2. Visometerytested oils, both bio and mineral, showed the same behavior. In order to investigate thepoints of hange, where the oil started to deviate from the exponential funtion, visosityat low and high temperatures was interpolated by dierent exponential equations, as isshown in gure (3.2). The intersetion between the two equations was onsidered as thehanging point in the oil's behavior. It varied from 38 to 48 ?C; the highest temperaturewas with the bio-hain-saw oil.Figure 3.1: Visosity versus temperature of dierent oilsTo inrease the redibility of the interpolated equations, other equations were tested.The best ts were ahieved using double exponential equations. Figure (3.3) shows theimprovement in redibility due to the double exponential funtion. The onstants ofthese equations are listed in table (3.1)403.2. VisometeryFigure 3.2: Failure of single exponential funtionFigure 3.3: Credibility of double exponantial funtion in representing the visosityhange with respet to temperature of bio-hydrauli oil413.2. VisometeryTable 3.1: Constants for double exponential regression? = ae?bT + ce?dToil a b  d Tested domain1 Bio-hydrauli oil 0.20848 0.06574 0.04112 0.01781 [ 0oC ? 100oC ?2 Bio-gear oil 0.22883 0.0701 0.05265 0.02006 [ 0oC ? 100oC ?3 Bio-hain saw oil 0.09093 0.13744 0.10063 0.01274 [ 0oC ? 20oC ?4 Bio-hain saw oil 0.18533 0.07195 0.0621 0.02215 [ 20oC ? 100oC ?5 Mmineral hydrauli oil 0.41847 0.08351 0.05605 0.02344 [ 0oC ? 100oC ?3.2.2 Moderate Shear RateShear ramp tests were onduted several times on the same sample at dierent tempera-tures, from low to high; also the shear inreased aording to the logarithmi step. Theresults were plotted in gure (3-4). No reliable indiation of shear thinning or thikenningwas noted unless in ase of bio-hain saw oil at 0oC whih is still slight also. The veryslight hanges at high and low shear rates ould be attributed to seondary ow, heatdissipation, and stability. The same slight hange ould be measured in silion oil also,whih is a Newtonian oil. It seems that polymer improvers were avoided in the ommer-ial mineral oil in order not to aet its degradability. Consequentially, the assumptionof vegetable oils as Newtonian uids an be expanded to inlude tested bio-lubriants. Itshould be pointed out that the typial shear rate in pipe ow is 100 to 103, whereas thetypial shear rate with lubriation varies from 103to 107[79?. Thus, further steps weretaken to test the bio-hydrauli oil at a high shear rate, and ompare it with ommerialengine oil.423.2.VisometeryFigure 3.4: Visosity versus shear rate at dierent temperatures. a) bio-hydrauli oil. b) mineral hydrauli oil. ) bio-gearoil d) bio-hain saw oil433.2. Visometery3.2.3 High Shear RateAn apparent ontrast between engine oil and bio-hydrauli oil is illustrated in gure(3.5). Even though the engine oil is a diluted polymer solution, the shear thinning wasobvious at a high shear rate that agrees with referene [42?. Figure (3.6) represents thenormal fore versus the shear rate. While in the ase of the engine oil, the normal foreinreased with respet to the shear rate, in the ase of the bio-hydrauli oil, the normalfore stayed under zero. The negative normal fore was due to the inertia eet. Theassumption that bio-lubriants are Newtonian uids is still valid at high shear rates,also. However, this is a trivial solution beause it does not give muh information, ortell us what the dierene between oil and water is. Thus, we reognized the need forfurther investigation into the visoelastiity of bio-lubriants, and the ndings will bepresented.Figure 3.5: Visosity at high shear rate, bio-hydrauli and engine oils443.2. VisometeryFigure 3.6: Normal fore at high shear rate, bio-hydrauli and engine oils3.2.4 Yield StressYield stress was measured only in bio-hainsaw oil, at temperatures under 20? C. Inter-estingly, this is the same area in whih bio-hainsaw oil diered from other oils. Morework on bio-hydrauli oil will reveal the existene of yield stress, but it takes a longertime to build up. In fat, yield stress is the rst sign of non-Newtonian behavior. Itwas found that temperature history inuened the results, but faded with time. Yieldstress is demonstrated in the visosity-shear stress diagram, as shown in gure (3.7).The same sample was tested at dierent temperatures, from high to low, after it wasgiven 5 minutes to rest. Calulated yield stresses using linear regression are 0.0177 &0.008 Pa at temperatures 0 & 5? C respetively.453.3. Small Amplitude Osillatory Shear (SAOS)Figure 3.7: Yield stress in bio-hainsaw oil3.3 Small Amplitude Osillatory Shear (SAOS)Even though the fous was on bio-hydrauli oil, dierent oils were tested for the purposesof omparison and validation. Assumedly, all bio-lubriants behave similarly. The behav-ior of bio-oils is omplex. The oils are deliate materials, i.e., they are time dependent,path dependent. Only the results that were onviningly repeatable and explainableare reported. However, it should be stated that there is no guarantee of getting thesame results again, unless the same irumstanes are provided. Furthermore, in manyases the used rheometer apabilities were taken to the end of range; another rheome-ter with lower speiations would not be able to get the same results, aurately. Wewere areful to use the same experiment setups on the dierent samples, espeially whenomparison was intended. Moreover, an eort was made to unify the preonditions, aslisted below:- Temperature, a new sample for every temperature was used, to avoid any hysteresiseet, unless the test itself required temperature hanges. Five minutes was given to463.3. Small Amplitude Osillatory Shear (SAOS)samples to stabilize. The ooling and heating rates were neither taken into aount norstudied.- Surfae onditions; it was noted that bio-lubriants gave dierent results aordingto how the geometries were leaned, i.e., with a paper towel, detergent, or ethanol. Thesoniation bath was not available in the lab, so the geometries were leaned using ethanoland then with ame several times until geometry leanness beame obvious.- Pre-shear. Two types of osillatory proedures were onduted in this researh:either ontinuous osillation or osillation with shear intervals in between. It was notedthat every shear ould lead to dierent states in values or patterns. Figure (3.8) skethesthe multi-osillation proedure. The shear in the interval periods was set to zero in thease of the reported results.- Time: it was found that G' is time dependent. All the following experiments,whih are not funtions of time, were performed 5 hours after applying the sample,approximately. It is estimated that bio-hydrauli oil reahed 95% of its steady state after5 hours, with a gap of 0.3 mm. This estimation is based on polynomial extrapolation.A test on time dependene will be presented.Figure 3.8: Illustrative input signal of multi osillation proedure473.3. Small Amplitude Osillatory Shear (SAOS)3.3.1 Osillation AmplitudeThis test is an essential step for further tests to determine the limits of linear visoelasti-ity, whih was found to be 10% aording to gure (3.9). The linear visoelastiity, whereG' is independent of osillation amplitude, ould be lower than 10%. Though a prioritywas given to gaining more preious torque, when the lower amplitudes were heked witha frequeny sweep test, no signiant hanges appeared in the results. The linear limitwas heked at dierent temperatures, and gave the same limit, approximately.Figure 3.9: Linear visoelastiity limit of bio-hydrauli oil at 1Hz frequeny3.3.2 Time Dependeny of the Elasti ModulusFigure (3.10) summarizes the results of the multi-osillation tests of dierent samples.The gaps and frequenies were 0.5mm and 1Hz, respetively. Beside bio-hydrauli oil,engine oil and silione oil were tested for the purposes of omparison and validation.Only bio-hydrauli oil showed a growing G'. This hange ould be result of dierentativities, for example: drying, oxidation, aruing, or mirostrutural hange. If any of483.3. Small Amplitude Osillatory Shear (SAOS)these reations take plae, exept mirostrutural hange, the hange will be permanent.This raises the question of whether or not the G' an be deonstruted and reonstrutedagain.Figure 3.10: Time dependene of the dynami shear modulus G? for dierent oils at 0?C3.3.3 Frequeny SweepA frequeny sweep test was onduted on bio-hydrauli oil under a gap of 0.3mm. Fig-ure (3.11) plots G' and G with respet to frequeny, and Figure (3.12) summarizesthe relation between G' and temperature. The last experiments not only revealed thevisoelastiity of bio-hydrauli oil but also the solid-like behavior in whih G' exeedsG at low frequenies. G' hit its plateau region under the frequeny of 1Hz.493.3. Small Amplitude Osillatory Shear (SAOS)Figure 3.11: Frequeny sweep of bio-hydrauli oil at dierent temperaturesFigure 3.12: Storage modulus of bio-hydrauli oil at 1 Hz versus temperatureIn other researh, using SAOS on holesteri liquid rystals with inlusions exhibited503.4. Low Shear Ratesimilar behaviour [34?. Further, it was mentioned that it also exhibited the typialbehavior of a Maxwell uid at an angular frequeny of more than 10 rad/s, while itshowed lear features of gel-like behavior at a lower frequeny. Comparably, we foundthat the Maxwell model an t the bio-hydrauli oil at a temperature of 0oC and atan angular frequeny of more than 60 rad/s. Consequently, the relaxation time is 0.93mse. The tting of the Maxwell model is shown in Figure (3.13).Figure 3.13: Maxwell model ts bio-hydrauli oil's result at 0?C3.4 Low Shear RateAfter the nature of G' time dependeny was reognized, it beame neessary to hek thevisosity against the shear rate again, this time at a very low shear rate, whih allowed forenough time for to G' to grow. Figure (3.14) learly shows the shear thinning behaviorof the bio-hydrauli oil while temperatures are below 30?C. There was no tendeny toreah the plateau visosity at very low shear rate. This predits the presene of yield513.5. Gap Size Inuene on Elasti Modulusstress; meanwhile it strengthens the redibility of the frequeny sweep results in thesense of exhibiting solid-like behavior at a low frequeny.Figure 3.14: Shear thinning behavior of bio-hydrauli oil3.5 Gap Size Inuene on Elasti ModulusGap size eet was investigated in the ase of bio-hydrauli oil; the summarized resultsin gure (3.15) show a strong relevane to G'. While G' dereases with gap size, Ghanges slightly. This onrms that the variation in G' annot be due to the gap errors.G' reahed either a peak or a onstant value after a ertain gap size. Even though thisbehavior was predited more by the urve tting, it is more obvious in the ase of thebio-hainsaw oil (gure (3.16)),where, the hange was sharper. In an eort to explainthis phenomenon, we assume two senarios and the third is a ombination of the rsttwo. The rst assumption is that the struture of bio-oil is relatively large with respetto gap sizes of less than 0.6mm. The seond senario is that the bio-oil's struture is523.5. Gap Size Inuene on Elasti Modulusaeted by its ontat with the geometry surfae, and this eet beomes more obviouswhen the gap beomes narrower. In the literature, gap size eet was investigated on aNano sale base in the ase of n-hexadeane [82?.Figure 3.15: Eet of gap size on elasti and loos moduli, bio-hydrauli oil at 0?C and1 Hz533.6. The Deliate Struture of Bio-hydrauli OilFigure 3.16: Eet of gap size on shear moduli, bio-hainsaw oil at 0?C and 1 Hz3.6 The Deliate Struture of Bio-hydrauli OilThe previous results proved how the state of bio-oil is a funtion of temperature, time,and oupied spae. In addition, it was aeted by pre-shear. This is another sign of thepresene of struture. This deliate struture an be built over time and deonstruted byshear. In order to demonstrate this behavior, a omplex visometery test was onduted.The test has three sequential proedures, whih are explained in gure (3.17) . Theresponse to the input signal is presented in gure (3.18). The visosity inreased in alogarithmi manner as result of the rst proedure, whih involved a onstant appliationof very low shear stress for 5 minutes. The seond proedure was growing a shear ramp,and gave the expeted shear thinning behavior. The third proedure, whih was the sameas the seond in reverse growth, deviated in its result from the seond one, whih is asign of hysteresis behavior. The three proedures draw a omplete loop on the visosity-shear rate diagram. It is worth mentioning when the rst proedure was repeated again,543.7. Struture Reovery of Bio-hydrauli OilFigure 3.17: The input signal of multi proedure experiment (3.18)the visosity followed the same path but at a muh slower rate. The explanation forthis omes from the sample history. Whereas the rst proedure was preeded by atest under the linear limit, the fourth proedure was preeded by proedure 3, whihexeeded the linear limit.3.7 Struture Reovery of Bio-hydrauli OilThe previous experiment demonstrated struture building and struture reovery. Con-sidering G' is a more reetive property of the miro struture of the oil, it is meaningfulto use G' to test struture reovery. As explained in the literature [77?, the SAOS wasused to study struture reovery, rystallization, and aruing [36?. This test onsistsof three proedures, whih are single frequeny osillation tests. While the rst and thelast were performed under linear limits, the seond had a substantially larger amplitudethan the linear limited tests. The purpose of organizing the tests in this way is to allow553.7. Struture Reovery of Bio-hydrauli OilFigure 3.18: Visosity of bio-hydrauli oil due to sequential multi shear testthe struture to grow up; destroy the built struture; and, nally, observe the struturereovery in the last proedure. The struture reovery has important impats on ertainappliations, suh as inking [77?. In the ase of lubriation, the impat of struture hasnever been studied. An experiment was onduted twie on the bio-hydrauli oil, at 0.4mm and 0.2 mm gaps. The frequeny was 1Hz. The osillation amplitudes were 10%,500%, and 10%. The results are presented in gures (3.19, 3.20) and summarized intable (3.2).Table 3.2: Summery of struture reovery tests on bio-hydrauli oilaverage growing rate of G' (Pa/h) Perentage of derease in G' dueto over shearing osillationGap First proedure Third proedure0.2 mm 0.0152 0.0155 27.2 %0.4 mm 0.0171 0.0145 33.3 %The G' growth after over-shearing followed almost the same pattern as in the rstproedure. The derease in G' varied from 27.2 to 33.3%. This gives an indiation of563.7. Struture Reovery of Bio-hydrauli Oilstruture stability. However, we do not have a omparable ase to estimate the strengthof the struture. The larger gap was aeted more; the Reynolds number was largeralso. It is like a quik mixing of a Lego struture. It will be destroyed , but it will notlikely return to single piees, as it was originally. The sharp dereasing in G' that tookplae after 12 minutes is not a random behavior. It is a repeating phenomenon andshows up more learly in the smaller gap.Figure 3.19: Struture reovery of bio-hydrauli oil at 0.4 mm gap573.8. Rheometry as Tehnique to Study Surfatant BehaviorFigure 3.20: Struture reovery of bio-hydrauli oil at 0.2mm gap3.8 Rheometry as Tehnique to Study SurfatantBehaviorBased on the previously presented work, many indiations have led to the onlusionthat some surfae ativity between the oil and the geometries do aet the rheologialbehavior. The self-assembled monolayer is a nano-phenomenon. And while some nanotools are used to study it, suh as analytial transmission eletron mirosopy (ATEM)and atomi fore mirosopy (AFM), some maro tehniques are also used to measurethis reation, suh as surfae tension and LangmuirBlodgett trough. Using a rheometerto study the surfae ativities is new.583.8. Rheometry as Tehnique to Study Surfatant BehaviorFigure 3.21: Elasti modulus versus time at gap 0.2 mm and frequeny 4Hz3.8.1 Impat of Surfae Conditions of the Geometry onRheologial BehaviorWe aimed to demonstrate the eet of the self-assembled layer on the bulk properties ofbio-lubriant. Single amplitude osillation was used to observe the behavior of G'. Thegeometry was leaned in the rst experiment using the mentioned method, whereas itwas only wiped out with a paper towel in the seond experiment. The surfae in theseond experiment was lean apparently. We did not ondut any analysis to diagnosethe surfae hemial omposition, but we assumed that the self-assembled layer-or partof it- stayed on the surfae if it indeed existed. The result is reported in gure (3.21).We rst noted that the not-leaned surfae had a lower G' and a smoother urve.This supports the assumption that the inreasing G' with respet to the gap size ouldbe due to the elimination of the surfae eet. The smother G' growth is a possibleindiation that the self-assembled layer was already developed and any reation with593.8. Rheometry as Tehnique to Study Surfatant Behaviorbulk properties took plae early. The sharp drop in the G' that we reported beforeappeared in this experiment also. Moreover, it happened again after three hours. If thetwo experiments, with lean and not lean geometry, would ultimately lead to the sameregime, other drops in G' would be required to meet both urves.3.8.2 Impat of Geometry's Material on Rheologial BehaviorA further step was taken to investigate the eet of the surfatant behavior using SAOS.The geometry used was stainless steel made, but it was also overed by a sheet of plasti0.17mm thik. The inuene of the geometry material was measured, and gure (3.22)shows the results of four frequeny sweep experiments at dierent gaps. Firstly, thesample was tested at a gap of 0.5mm, whih was then squeezed to 0.2 mm and testedagain. The systemati repeating eet of the ontat surfae material on the rheologialbehavior was identied in the results. In addition, the dierene in G' due to using plastiand stainless steel geometry inreased with dereasing the gap. (Note the dierenebetween h1 and h2 on the graph). One again, this supports the idea that one of thereasons behind G's gap size dependene omes from the reation with the surfae.The above experiment was onduted again, but with 2% tetrauoroborate added tothe hydrauli oil. The added material, ioni liquid rystals (ILC), is a strong surfatantthat have been used in previous researhes as lubriity improvers. More details willome in hapter (5). The objet of this experiment was to hange the mirostruture andsurfatant nature of bio-hydrauli oil. Thus, if a hange is observed in the bio-lubriant'sbehavior against geometry materials and gaps, it will onrm the last onlusion whihis the eet of the surfae extends and aets the bulk properties of the oil. It shouldbe pointed out that the sample was replaed in order to hek another gap size, insteadof squeezing the larger gap, as before. Where squeezing the gap made a sharp hangein the sample behavior, in ontrast, the bio-hydrauli oil's G' did not show a signiant603.8. Rheometry as Tehnique to Study Surfatant BehaviorFigure 3.22: Frequeny sweep test of bio-hydrauli oil at 0?C, and with dierent geometrymaterialsdierene between the squeezed or ompletely replaed sample. Remember that bio-hydrauli oil is a more homogenous material than the ILC solution. We doubt that theILC onentrated beside the surfaes, so the squeezing hanged the onentration of thesample.Figure (3.23, 3.24) represents the results in the ases of replaing and squeezing thesample, respetively. The eet of the gap size and geometry materials is less importantin this ase. On the other hand, the hange in behavior due to the gap hange wasmore obvious, espeially in the ase of the stainless steel geometry. Meanwhile, theplateau region beame unlear in the ase of the 0.2 mm gap & stainless steel surfae.We wonder if the ILC took, or ompeted with, the bio-oil settling on the surfae. Thiswould aet the boundary regime and how it interated with bulk uids. Interestingly,the eets of the additives not only appeared on the readings, but ould also be seen inthe samples after the test. Figure (3.25) shows pitures of the bio-hydrauli oil and the613.8. Rheometry as Tehnique to Study Surfatant BehaviorFigure 3.23: Frequeny sweep test of 2%ILC at 0?C with dierent geometry materials,the sample was replaed2% ILC samples taken immediately after the geometry was lifted up.Figure 3.25: Pitures of the samples after tests on the lower plate623.9. Polarized Light MirosopyFigure 3.24: Frequeny sweep test of 2% ILC at 0? C; the sample was squeezed3.9 Polarized Light MirosopyAording to the results, a number of onsistent behaviors led to the idea that bio-lubriants behave like liquid rystals. One thing known about liquid rystals is theirinteresting interations with light. In order to investigate this assumption more thor-oughly, we used a polarized light mirosope, Anton Paar brand, to examine our samples,whih is shown in Figure (3.26). Compared with the emulsion of water in bio-oil, thebio lubriant did not at as a strong transitive to polarized light, though it showed in-terations with light aording to temperature and applied shear. Pitures of some seenevents are reported in Figure (3.27).633.9. Polarized Light MirosopyFigure 3.26: Anton Paar, polarized light mirosopeFigure 3.27: Polarized light mirosope pitures on Anton Paar rheometerThe gap was about 0.1 mm under a at aryli geometry. The heating rate was about8?C/minute. Gap size and heating rate had not been studied. Many views through thepolarized mirosope support the assumption about liquid rystals. The following are643.9. Polarized Light Mirosopythe most important notes:? The bio-lubriant's interation with polarized light depended on the temperature.? The light ativity stopped at temperatures under -15?C. This ould be due to theoil starting to solidify, and any motion by moleules to align themselves beamediult.? Changing the temperature without a shear did not hange the state of the trans-mitted light, remembering that the heat rate was high. In ontrast, a signianthange took plae when the hange in the temperature was assoiated with shear.Possibly, the shear helped the moleules to move and align themselves.? A temperature of about 40?C marked a hanging point in the bio-oil's behavioralso for polarized light mirosopy, bak to (2-2-1).? A periodi hange in olour was noted under the shear. While these hangesinreased with the shear, no lear borders between one olor and another were no-tied. However, the hange in olour showed more ontrast, whih meant that bor-ders were more easily identied in the mixture between mineral and bio-hydraulioil of 80/20. In addition, the ontrast in olor not only appeared in a sequentialperiodi manner, but also showed up in separate objets similar to meteors. Theseare shown in gure (3.27).? Some dark aggregates appeared in the mixture of bio-oil with holesteryl hloride(LC). We ould not see if they were in a rystalline phase or merely undissolvedpartiles.653.10. Liquid Crystal Additives3.10 Liquid Crystal AdditivesWhile it was deided that tribologial experiments ould evaluate the performane of thelubriant quantitatively, we needed something more than that to explain the mehanismof that performane. The results of tribologial tests of two solutions of liquid rystals,with bio-hydrauli oil, will be given in hapter (5). The liquid rystal solutions are2% tetrauoroborate (2% ILC) and 10% holostryl hloride (10% LC). The ultimategoal is to make a onnetion between their tribologial and rheologial behaviors. Whilevisoelastiity ould give an indiation of the mirostrutural nature of the lubriant, thevisoelastiity ould give an indiation of the reation between the moleules of base oiland the additives. However, it is not lear what the relation between the mirostrutureand the lubriity is. This experiment is an eort to nd this kind of onnetion. Weused a single frequeny osillation test under a onstant heating rate of 0.5?C/min. Thetest overs a temperature domain of between -5 to 100? C. Figures (3.28, 3.29) plot Gand G' versus temperature. In terms of G, both liquid rystal solutions aeted thethermal stability of the visosity, while they kept the same behaviour along most of thetemperature domain. However, G inreased sharply at temperatures below 0?C, in thease of 2%ILC. By ontrast, G' had dierent values in the ase of 2%ILC, and showeda dierent pattern that was almost onstant along the temperature domain. Neitherthe temperature rise nor the small shear amplitude was able to break the struture thatourred at the low temperatures, assumedly . LC lowered the G' and followed a similarpattern to that of the pure bio-hydrauli oil.663.10. Liquid Crystal AdditivesFigure 3.28: Osillatory temperature sweep, loos modulus (G)Figure 3.29: Osillatory temperature sweep, elasti modulus (G')673.11. High Pressure Rheology3.11 High Pressure RheologyLubriating is usually assoiated with high pressure. While the pressure ould exeedone MPa in the hydrodynami regime, it ould exeed one GPa in the boundary regime.High pressure auses inreases in both the density and visosity of oil .The used highpressure ell mounted on Anton Paar rheometer is shown in gure (3.30). The pressureell has a apaity of 0.4 GPa, depending on the pressure of the supplied ompressed gas.It is ompletely sealed, with a ylinder and up inside, and the torque is transmittedvia magneti oupling. The ompressed gases used were CO2 and N2, and the resultsof CO2 are presented in gure (3.31):Figure 3.30: Anton Paar high pressure ell (reprodued image) [83?It was found that the visosity of bio-hydrauli oil was inversely proportional to thepressure when the ompressed gas was CO2. Figure (3.31) is the relation between thevisosity and the pressure in the ase of CO2. We believe that the absorbane of CO2into the oil was responsible for the derease in visosity, whih was extensively releasedafter the pressure ell was opened, in a manner similar to boiling.683.11. High Pressure RheologyFigure 3.31: Visosity of bio-hydrauli oil under pressure of CO2Figure 3.32: Bio-hydrauli oil visosity versus CO2 pressure drop, maximum pressure3.6 MPaNo alibration was done to estimate the gas esaping from the ell, but the dereasing693.12. Conlusionsvisosity with time onrms that the drop in the visosity was due to the CO2 beingabsorbed. Figure (3.32) shows the relation between the visosity and the pressure drop.Aordingly, it is diult to deide the impat of the shear rate, where a higher shear rateould inrease the mixing and exposure to the CO2. Dereasing visosity with respetto CO2 pressure was reported in a study on orn oil and onneted to the dissolution ofCO2 [28?. In ontrast, the visosity inreased with respet to the pressure when N2 wasused instead. This is represented in gure (3.33), where the visosity inreased about6% by inreasing the pressure from 0.13 to 1 MPa.Figure 3.33: Visosity of bio-hydrauli oil under pressure of N23.12 ConlusionsWhile most of our eort were foused on bio-hydrauli oil, the experiments that wereonduted on the three samples of bio-lubriant showed onsiderable similarity. Thebio-lubriant has a onstant visosity at moderate and high shear rates. Aordingly, its703.12. Conlusionssimilarity to Newtonian uids is valid for most appliations. In ontrast, visoelastiitywas investigated using SAOS, and shear thinning was noted at a very low shear rate. Itwas found that the visoelastiity of bio-oil is funtion of time, temperature, gap, andsurfaes materials, whih means revealing important information about its mirostru-ture and surfae ativities. The experiments onduted onsistently led in the diretionof our assumption of its similarity to Liquid rystals. Further, something is formattingon the surfae and dereasing the G'. Meanwhile, the self-assembled mono layer has anorganized struture. Thus, if it extends in the diretion of the uid, the extended lay-ers will be likely organized, too. The extended monolayer was reported before in someresearhes, but in nano level [82?. As a result, we are imagining two existing phasesof liquid rystals at least; they ompete with eah other, as was shown in the gap sizeand geometry material eets in setion (3.8). We expet that the boundary phase isSmeti while the bulk phase ould be omplex. This idea is illustrated in gure (3.34).Figure 3.34: Imaginary simplied senario of bio-hydrauli oil rystallization within asmall gap71Chapter 4Thermal Analysis4.1 OverviewThermal Analysis (TA) means the analysis of a hange in a sample property, whih isrelated to an imposed temperature alteration. Calorimetry means the measurement ofheat [85?. Change in a sample ould be due to a hemial reation, biologial ativity,mirostruture, or phase transition [86?, whih means that TA ould reveal importantinformation, for instane: spei heat, omposition, oxidation and thermal stability,aswell as dierent harateristi points that indiate glass transitions, melting, boiling,and rystallization. The main fous of this hapter is to onnet rheologial and thermalbehavior, while also investigating the hanges in mirostruture. Some transition pointswere observed in the results, suh as pour point. However, they will not be disussed indetails beause parallel experimental work is needed to be able to read on the TA urvesorretly. Dierential Sanning Calorimetry (DSC) is the TA tehnique that was usedin this study. It involves measuring the heat ow with respet to temperature under theprogrammed heating rate. The heat ow is determined by the following equation:dQdt = ?Cp (4.1)Where Q is heat, t is time, ? is heating rate Cp is heat apaity. The heat apaityis the only material property showing in the last equation.724.2. Experimental Setup Apparatus4.2 Experimental Setup ApparatusFigure (4.1) shows multi-ell dierential sanning alorimeter, MC-DSC4100, whih wasused in this researh. It is furnished with four ampoules whih an host three dierentsamples in the same experiment while the fourth works as a referene. The ampouleswere made of stainless steel with srewed aps. MC-DSC 4100s an over temperatureranges from -40 to 110oC with a heating rate from 0.1to 2oC/min, and sensitivity 1?W [87?.Figure 4.1: The alorimeter used, MC-DSC4100The heating rate for all the results presented here is 0.2oC/min. The temperatureranges from -30 up to 100oC. Sine the DSC experiened instability during startup, it was eliminated. The same experiments were done on empty ampoules, and anydeviations from zero were subtrated from the results. The ampoule leaning and samplepreparation are detailed as follows:Ampoule leaning: The ampoules were rinsed and soniated for 10 minutes withdierent solutions: detergent, nano-pure water, ethanol, nano-pure water twie, andnally, methanol. Then, they were left to dry in the ambient temperature before puttingthem in the oven at 80? C for 1 hour. The ampoules were weighed before lling, after734.3. Resultslling, and after the test, using a digital sale.Sample preparations: All tested samples were degassed using a vauum hamber.They were injeted slowly at the lower surfaes of the ampoules using lean syringes.4.3 Results4.3.1 Repeatability and ReversibilityA heating-ooling-heating test on the bio-hydrauli oil was repeated twie; the rst andseond heating runs gave almost the same results, within a range of 0 to 100? C. Thus,no permanent hange had taken plae, and the mirostruture of the oil was reoverablewithin the tested domain. Figure (4.2) shows the heating and ooling urve of the 0.56gof bio-hydrauli oil. While we expeted the existene of a gap between the heating andooling urve at a high heating rate, it dereased at the lower heating rate [88?. Inother words, the lower heating rate gave the oil enough time to develop its struture.The urves overlapped from 10 to 50?C, and separated again after that. This preditsthe existene of another peak at temperature above 100? C, assumedly. The ooling teststarted from 110?C, so this high temperature ould aet the following lower temperaturebehavior on the ooling urve.4.3.2 Sample SizeIdeally, the size of the sample should not inuene the result, yet gure (4.3) reveals arelationship between the sample mass and ejeted heat. This eet not only translatedinto dierent values, but also aeted the pattern of the urves. While urves of 0.18gand 0.56 g keep in parallel, the urve of 0.05 g shows a dierent behavior. Based on ournotes, this behavior was more likely real than merely the result of errors. The dierenebetween urves 0.05 g and 0.18g beomes learer at temperatures from 0 to 25? C. This744.3. ResultsFigure 4.2: The DSC heating and ooling urves of bio-hydrauli oilis the same range at whih the bio-hydrauli oil has relatively high G' aording to therheology results. Curves for 0.05 g and 0.18 g orrespond to eah other at intervals lowerthan -13? C. This agrees with the polarized mirosopy results in setion (3.8). Curve0.05 g has a form of ar that is tangential to urve 0.18g at around 45?C. The sharp droparound 71?C inreased as the mass dereased. While smaller mass samples have smallerdepths, the eets of walls will be larger. Assuming that the oil has a struture thatould be initiated or stimulated by metal walls, this an explain the impat of samplesize on DSC results.4.3.3 Transition PointsTransition temperatures were loated on the DSC heating urve of the 0.05 g sample(see Figure 3-4). While dierent points ould show up on a ooling urve, they will notbe disussed beause they ould be the same points under lagging. The used apparatushas a defet at around 20?C, so any event around that temperature annot be taken754.3. ResultsFigure 4.3: DSC ooling urves for dierent mass samples of bio-hydrauli oilinto aount. The interesting thing about this urve is that the transition points werenot assoiated with lower temperatures exlusively, but also ourred at relatively hightemperatures, like 60?C. It was diult to investigate G' at that region due to obviouspratial diulties. It was noted that the drop that happens at around 60oC doesnot show up at a faster heating rate. This is understandable beause it is a sharpevent, and any faster heating rate will miss it. They ould be two neighbouring drops,but the double drop appeared only on the small sample. A drop of around the sametemperature was reported on the DSC of palmiti aid [36?, and not far from it wasmeasure in sediment that was extrated from anola oil [63?.A similar behavior was reported by a study on undatus seed oil [60?. The last refer-ene reported suh details on DSC transition points of bio-oil. Additionally, Endothermiheat ow ontinues to rise up, even at relatively high temperatures, similarly to whatwe measured. Consequently, it was seen as a good ase to ompare our results with.Table (4.1) lists transition points for dierent oils. In terms of hemial omposition,764.3. ResultsFigure 4.4: Transition points on heating the DSC urve of bio-hydrauli oilundatus seed oil is not muh dierent from anola oil. A omparison between both isfound in table (4.2). In ontrast, undatus oil has more than double the saturated fattyaids that anola oil has. Is this the reason behind the fat that the transition pointsin the undatus oil ase are more distinguishable Finally, where the saturated fatty aidshave greater tendenies to rystalize, olei aid has the opposite [59?.Table 4.1: Comparison transition points [58,61,34?SampleTransition temperature on melting urve (?C)1 2 3 4 5 6Canola oil OOR -20 -16.5 - 6.5 60Undatus oil -35.75 -25.39 -16.77 -5.64 5.46 OORPalmiti aid OOR OOR OOR OOR OOR 62.7Canola sediment OOR OOR OOR OOR OOR 75.2-78.7OOR: out of the range774.3. ResultsTable 4.2: Comparison between hemial omposition of anola oil and undatus [13, 14,60?Fatty aid Canola oil Undatus seed oilPalmiti (C16:0) 3.68 12.78Steari (C18:0) 1.65 4.67Olei (C18:1) 63.49 24.43Linolei (C18:2) 20.05 55.63Linoleni (C18:3) 9.46 1.18Saturated fatty aid 7 17.994.3.4 Dierent Bio-lubriantsBesides bio-hydrauli oil, bio-gear oil and bio-hainsaw oil were sanned as well, andthe results are reported in gure (4.5). The tested sample masses were 0.378g, 0.49 g,and 0.56g respetively. A onnetion between DSC and rheologial behavior was foundagain. Bio-gear oil and bio-hydrauli oil had parallel urves, whereas the bio-hain sawoil deviated from them at very low temperatures. When omparing this with theirrheologial behavior, bio-hain oil showed dierent behaviors at low temperatures. Thegap between bio-gear and bio- hydrauli ould be narrower if they had the same mass.4.3.5 Impat of Liquid Crystal Additives on DSCAs to the heating urve, Figure (4.6), the three samples behaved similarly. If the size ofthe sample mass is onsidered, bio-hydrauli oil ould have larger absorbed heat. Thesample masses of bio-hydrauli, 2%IL and 10%LC, are 0.56, 0.37, 0.37 g, respetively.The sharp hange ame in the ooling experiment, where the 2%ILC sample did notejet any heat energy, relatively. We negleted the possibility of the sample esapingdue to evaporation or oxidation, as the ampoules were saled after the test. Eithera hemial reation had ourred, or a strong struture that ould be destroyed by atemperature hange had taken plae. However, it is diult to onrm this big hangewithout repeating the test several times. It should be pointed out that the same sample784.3. ResultsFigure 4.5: DSC ooling urves of dierent bio-oil sampleswas used in both the heating and ooling proedures.Figure 4.7: DSC ooling urves of bio-hydrauli oil plus liquid rystal additives794.3. ResultsFigure 4.6: DSC heating urves of bio-hydrauli oil plus liquid rystal additives4.3.6 Comparing Between DSC and Rheologial BehaviorRealling the osillatory temperature sweep (3.10), the G' urve from the SAOS is on-sistent to some extent with the heat urve from the DSC tests, as shown in gure (4.8).This inreases the redibility of the results.804.4. ConlusionFigure 4.8: Comparing the SAOS and DSC tests on bio-hydrauli oil (The heat ow axisis in reverse order for the purposes of lariation)4.4 ConlusionThe TA results agreed to an enouraging extent with the literature, as well as withthe rheometery and mirosopi results. Comparing the noted transition points withthose in the literature ould reveal the omponents that have the greatest eet onrystalization in bio-lubriants. The inuene of the mass on the DSC urves ould betaken as indiators of surfae ativities. And while the orrespondene between DSC andSAOS was not strong, it was nevertheless onsiderable. Both the ooling and heatingurves followed similar and lose paths. A transition point at temperatures higher than100?C was predited based on the dierenes between the two urves.81Chapter 5Tribology5.1 OverviewThe onept of frition regimes was introdued earlier in the introdution. For the sakeof lariation and uniation of the terminology for the reader, we present this shortoverview. `Wear' is the surfae damage or removal of material from one or both of twosolid surfaes in sliding, rolling or impat motion relative to one another [89?. While anyor all of several dierent mehanisms (adhesive, abrasive, impat, hemial and eletri)ould produe damage and material loss, the ations of two of them are illustrated below:Adhesive wear: regardless of whether it is uid or dry frition, this ation takes plaebetween nominally at surfaes rubbing against eah other. Under severe pressure, afragment from one surfae ould adhere to another. While adhered fragments separatedfrom their original surfaes, due to the shear ation, try to stay onneted to anothersurfae, may separate from both and beome wear partile. This proess an reverse inthe opposite diretion. Meanwhile, this phenomenon auses motion resistane and lossof mass. Figure (5.1) illustrates it.Abrasive wear: unlike the preeding one, this proess is not exhangeable in bothdiretions. as it was with preedent one. It takes plae when a rough harder surfae isrubbing against a softer surfae, so the wear is arued due to plasti deformation andfrature.825.2. Compression Investigation of Bio-lubriant LubriityFigure 5.1: Shemati drawing demonstrating the adhesive frition mehanism5.2 Compression Investigation of Bio-lubriantLubriityThe four-ball test or extreme pressure test was hosen for the purpose of investigatingthe lubriity of bio-lubriants. The nature of the surfaes of the ontating balls allow forahieving very high pressure, whih ould ause what is known as a weld or seizure point.Moreover, the surfae area generated from the wear is an important measurement oflubriant wear resistane. Getting dierent sars from every test makes it more redible,statistially. Besides, we tested mineral hydrauli oil for the sake of omparison. Sinethis ommerial oil was designed to be degradable and environmentally safe, it likelyhad restritions on the number of toxi and nondegradable additives it ould ontain.Thus, we annot onrm that this produt would perform the same as any onventionallubriant. Also, its visosity index is lower than the bio-lubriants. However, its gradewas hosen to make its visosity lose to bio-hydrauli oil as muh as possible at the testtemperature of 75 ?C. Eventually, in terms of the purpose and the grade it is omparableto bio-hydrauli oil.835.2. Compression Investigation of Bio-lubriant Lubriity5.2.1 ApparatusThe mahine we used was a Falex-6 multi speimen wear tester, gure (5.2). It has apair of aligned shafts, the upper shaft being the rotating one. The lower one is free tomove, and loaded by stati weights via a lever. The torque is measured by a torque ell.The rst three balls are lamped xed in an oil up that is plaed on the lower shaft.The 4th ball is entered above the rst three balls and rotating via the upper shaft.The temperature is ontrolled by eletri resistane heater, and measured by a thermoouple.Figure 5.2: Falex-6 (multi speimen wear tester)5.2.2 Experimental SetupBall bearings of 12.7 mmwere used. They were made of extra-polished steel E52100, witha hardness of HRC 64. They were leaned with detergent and aetone in a soniationbath before they were rinsed and dried with ompressed air. The oil up was ledwith oil up to 5mm above the balls. Then it was given enough time to reah a steadystate temperature before starting the test. The test onditions were hosen to be inompliane with standard test: ASTM D 4172  94 (2010) [90? as summarized in table(5.1):845.2. Compression Investigation of Bio-lubriant LubriityTable 5.1: Four-ball test onditionsBallApplied load Rotation speed Temperature Test timeMaterial DiameterSteel E-52100 12.7 mm 391.5 N 1200 RPM 75oC 1 hour5.2.3 RepeatabilityThe test on the ommerial lubriant was repeated three times. The sars' diameterswere measured twie in two perpendiular diretions. Thus, eighteen measurements gavean average of 469.3 mm, with a standard deviation of 8.4 and a variane of 13% .Theresults are summarized in Table (5.2).Table 5.2: Summarized results of four-ball testLubriant Sar diameter Average COF Minimum COF Maximum COF1 Bio-hydrauli 397 um 0.107 0.066 0.1332 Mineral hydrauli 469 um 0.165 0.090 0.1805.2.4 SarsThe sars presented in gure (5.4) were pitured using an eletron mirosope, thatshown in gure (5.3), and measured using an optial mirosope.Figure 5.3: Sanning Eletron Mirosope (SEM)855.2. Compression Investigation of Bio-lubriant LubriityThe average diameter of the bio-hydrauli oil sars was the smallest, 397 mm, om-pared with those of the mineral oil, whih were 469 mm. In the ase of the mineral oil,the balls sars were not only larger, but also relatively rougher, (see gure (5.4)). Thebio-hydrauli oil sars appeared in well-dened irular shapes, even though the wearwas onentrated in a narrow region in the middle of the sar. The balls ontatingareas were formatted in the shape of a irle, even without any wear due to the elastideformation [89, 93?. The ontating pressure was not uniformly distributed, but wasgoverned by the following equation aording to referene [93?:p = po(1?r2r2o) 12 (5.1)Where po is the maximum presure in the enter, ro is the radius of ontating area,r is the radius where the pressure is alulated . Consequently, it was expeted thatthe wear was onentrating in the entre and following the path of worn partiles ormotion. The sar was distinguished inside the irular area beause it was smaller thanthe stati deformation. Thus, in the ase of the bio-hydrauli oil, the real sar ould bemuh smaller than what was alulated based on the diameter.Figure 5.4: Four-ball test sars aptured using SEM865.2. Compression Investigation of Bio-lubriant Lubriity5.2.5 Coeient of the Frition:The frition oeient was alulated based on the equation (5.2) [92?, and the urveswere plotted against time, as in gure (5.5)? = 222.707MN (5.2)Where M is the measured torque , N is the applied normal fore . The onstant inthe equation is a funtion of the dimensions and geometry setup of the four ballsFigure 5.5: Frition oeient versus time for bio and mineral hydrauli oilsCommonly, the oeient of the frition is divided into dierent distinguished areasdue to the hanges in mating onditions between the rubbing surfaes: run-in and steadystate sliding. High asperities may be knoked o during start-up, whih will inreasethe real ontat area and mating surfaes. In addition, the thin upper surfae ould beworn out, or new surfae formatted on. All of these senarios ould lead to an inreaseor derease in the oeient of the frition. This period is alled the run-in period,875.2. Compression Investigation of Bio-lubriant Lubriitywhih is followed by plateau period. The plateau period is alled steady state sliding.The frition oeient ould rise up again after the plateau period, due to the eetsof roughening or worn partiles. This ould be followed by another plateau, whih isknown as an S urve, or it ould end in failure [89?.In the mineral oil test, the run-in period ontinued for three minutes approximately,followed by the plateau region. After that, the urve started to rise up again as a result ofthe roughening or worn partiles, as has been mentioned. In the ase of the bio-hydraulioil, there was no distinguishable run-in period until after almost 10 minutes. Evenafter the test was nished, a signiant part of the ontating area was still not learlysrathed. Preserving the same onditions on the surfae kept the frition oeient ataround the same value. Even after raising the frition oeient, there was no signiantinrease in the ontat area due to wear. Thus, it was not onrmed that the sar reaheda stable level [93?; neither it showed lear tendeny to inrease. In referene [95?, thewear rate had two onstant values periods and a jump in between. The ontat pressurehad a fall instead, simultaneously. It might have been a good idea to give the testenough time until the frition is ompletely developed, but it was timed for 60 minutesto fall in line with the standard. The researhes on frition generally and on wear testsspeially onrm a derease in the frition oeient, with respet to the real ontatarea. Referene [94? was dediated to investigating this phenomenon, and the resultsagree with most of the papers ited in this hapter. It is worth emphasizing that fritionoeient of bio-hydrauli oil was lower than that of the mineral oil, although it had asmaller ontat area. This indiates that the bio-lubriant has superior lubriity.885.3. Liquid Crystals as Additives to Improve Lubriity5.3 Liquid Crystals as Additives to Improve LubriityIt was mentioned in the introdution that liquid rystals are a matter of state for somematerials, whih have a less ordered struture than the solid state, whih gives thematerial distintive properties. Beause liquid rystals have good or superior lubriatingproperties, they an be used as additives to the oils.5.3.1 Samples and Experimental Setup5.3.1.1 Lubriants:In order to investigate the eet of liquid rystal additives on the performane of bio-lubriant oil, three dierent samples were tested:1. Bio-hydrauli oil.2. Bio-hydrauli oil plus 10 % of holesteryl hloride, (10%LC).3. Bio-hydrauli oil plus 2 % of 1-butyl-3-methylpyridinium, tetrauoroborate, (2%ILC).The additives were seleted based on their positive results with mineral oils. In addition,they were hosen beause of their diverse properties and hemial ompositions, in orderto over a wide range of study possibilities. Due to apital and time osts, we wereunable to test only a small perentage of additives and inrease it gradually. In ase ofone try, the perentage of additives was intended to be large enough to have a signianteet. Meanwhile, they were small enough to dissolve thoroughly in the oil.5.3.1.2 Preparation of 10% of Cholesteryl Chloride:The quantities were measured using a digital sale (10?4 g), and a 1 ml ordinary syringe.The smallest quantity that ould be added depended on the size of a drop, whih wasaround 0.01 g. Thus, the omponents with smaller mass sizes additives was saled rst,895.3. Liquid Crystals as Additives to Improve Lubriityand then the oil. Generally, the auray of saling was more than 99%. The loss inmass due to evaporation or adhering to beaker walls was not alulated. The mixturewas heated up to 95oC, using a temperature ontrolled hotplate. Meanwhile, it wasmixed using a magneti stirrer for one hour after reahing 90? C.5.3.1.3 Preparation of 2 % of TetrauoroborateThe mixture's omponents were measured in the same way as detailed above, and mixedup without any heating.Note: the prepared samples were used over several months. And, despite beingshaken gently before use, no physial hanges were observed by the naked eye.5.3.1.4 Pair of FritionChrome steel 52100 balls of 6 mm in diameter were used for this test. The disks weresheets of mild steel (C10-18) in thiknesses of 2 mm. They were polished manually bydierent grades of abrasive paper and diamond paste. The whole proess took about1 hour, as measurement to ahieved roughness. They were leaned with detergent andhot water before being rinsed with ethanol. Finally, they were dried by ame.5.3.1.5 Experimental SetupThe test onditions are summarized in table (5.3), whih were deided based on threevariables:1. Ahieving the maximum stress to ensure being in the frition boundary region.2. Giving the test enough time to observe the developing.3. Considering the apabilities of the apparatus.905.3. Liquid Crystals as Additives to Improve LubriityTable 5.3: Pin-on-disk test onditionsBall DiskMaterial Diameter Material DiameterChrome steel 6 mm Mild steel 24 mmNormal fore Rotation speed Veloity Test time Distane35 N 60 RPM 75.4 10?3 m/s 5 hours 1.36 103 m5.3.2 ApparatusFigure 5.6: Pin-on-disk setupWe used the Nanovea brand of the pin-on-disk setup, as shown in gure (5.6). Normalfore was applied using dead weights. The balaned state, zero position, was set upwith the aid of a digital sale. The frition fore was measured using a load ell. Afterbeing tested using dead weights from 1 to 20 N, it was found that the error followed alogarithmi funtion:?f = 0.0862ln(f) + 0.0986 (5.3)Where: ef is the error, and f is the atual measured fore. That gave us about a 5%error at 5 N. Part of this error ould be due to the swinging weights in the alibrationproess. The vertial displaement of the ball that gives an indiation of the wearrate was measured by a linear variable dierential transformer (LVDT). Compared withmetri gauges, it had an auray of 2 mirons. However, we ould not onrm that915.3. Liquid Crystals as Additives to Improve Lubriityerror ame from the LVDT or the metri gauges. Also, we notied that, during the rsttwo revolutions, the LVDT's reading moved up to 20 mirons. This initial deformationould be due to any elasti deformation or to the mahine itself. Thus, it was subtratedbased on two points: rstly, we wished to make the readings more reasonable omparedwith the nal depth of the sar. Seondly, this jump in the readings was almost onstantover all the tests. After all, this phenomenon was notied by other researhers, too [91?.The temperature was measured using a thermoouple, type K, that was plae on theupper surfae of the ball and onneted to a PC via a multi-meter. The thermooupleauray was tested using merury and a digital thermometer.5.3.3 Results5.3.3.1 TemperatureSine the apparatus did not have temperature ontrol, the tests were onduted at roomtemperature, 26oC. The temperature of the balls beame stable around 29 oC for all thetests. It was notied that the temperature of the ball was higher than the temperatureof the oil within 1oC. Figure (5.7) shows the reorded temperature for three tests.925.3. Liquid Crystals as Additives to Improve LubriityFigure 5.7: Temperature versus time for pin-on-disk tests5.3.3.2 Test QualityFigure (5.8) shows the variations in the frition oeient and LVDT readings for thethree samples at a revolution of 18x103, whih were loated at the end of the tests.All the samples had onsistent values at dierent angles, whih supports the redibilityof the tests' results, statistially. In terms of material homogeneity and tested sampletopography, we onsider this graph as an indiation of the test quality, espeially in theabsene of repeating the test several times.935.3. Liquid Crystals as Additives to Improve LubriityFigure 5.8: Distribution of the frition oeient and LVDT readings around the irularpath at the revolution 18x103.5.3.3.3 WearLVDT readings are plotted in gure (5.9). The wear in both bio-hydrauli and 2%ILC oils had four stages: growing up, plateau, growing up, and nally another plateau.Alternatively, this is alled an S urve [89?. In the ase of the 10% LC, the wear ontinueduntil it nally approahed a steady state. This agrees with referene [95?, where the wearalmost stops after the sar reahes ritial size. The proles of the nal sars on the diskswere measured using the LVDT at four positions around the path. These measurementsare reported in table (5.4) and gure (5.10). Even though the reading of the LVDT atthe end of the test was almost double the nal depth for the bio-hydrauli oil speially.all the sars were in the same depth approximately.945.3. Liquid Crystals as Additives to Improve LubriityTable 5.4: The measurements of the sars on the disksLubriantMax Depth of the sar Cross-setion area of the sarTotal wearAverage Variane % Average Variane %1 Bio-hydrauli 27.4 um 17.0% 0.0147 mm2 12.0% 0.555 mm32 10% LC 27.23 um 9.9% 0.0165 mm2 10.0% 0.623 mm33 2% ILC 30.9 um 19.0% 0.0146mm2 29.7% 0.553 mm3Figure 5.9: LVDT reading versus distane for 5 hoursThe maximum average wear on disks was obtained in the 10% LC ase, and thesmallest was in the 2% ILC ase. In ontrast, the depth ame in the opposite order.The omplexity of the tests requires more are in examining the results. Where the ballshad harder materials than the disks and the wear on them hanged the ontat area,the wear ould ontinue on the disks without hanging the ontat area and pressure,signiantly. Thus, it is more reasonable to onsider the size of the sars on the ballsas a good measurement of lubriity. The balls and disks were examined again underdisseting and a digital mirosope, (See gure (5.11)). The wear on the balls tookdierent patterns, whih are shematially drawn in gure (5.12). The wear in the ases955.3. Liquid Crystals as Additives to Improve Lubriityof the 2% ILC and 10% LC distributed around the sides, so the balls did not lose muhfrom their original heights, whereas in the bio-hydrauli oil ase, the wear took plae onthe tip. This explains the reason behind the dierene between the LVDT readings andthe depths of the nal sar. It was noted that the wear on bio-hydrauli ball was theroughest. Measuring the width of the sars using the LVDT or mirosope images gavedierent values. There is an inlination to onsider the largest value, whih ame fromthe mirosope image, beause it validates the assumption that the depth of the sar isinversely proportional to its width for all oils.Figure 5.10: Proles of the sars on the disksFigure 5.11: Disseting mirosope and digital mirosope965.3. Liquid Crystals as Additives to Improve LubriityThe largest sar on a ball was in the ase of the bio-hydrauli oil, while the smallestwas in the ase of the 2% ILC. Considering the prole of the sars on the disk, the 10%LC lost the largest volume while the 2% ILC lost the leastFigure 5.12: Pin-on-disk sars, a) shemati drawing for the mathing between ball anddisk; b) sar on ball, ) ball and disk; d) sar on disk5.3.3.4 Coeient of the FritionThe frition oeient was plotted against the sliding distane for the three samplesin gure (5.13), and the values are summarized in table (5.5). All the samples showeddened run-in periods. And, as to the four-ball tests, there is a omfortable agreementbetween them. The seond half of the bio-hydrauli oil urve had more importantvariations. Considering the sars, the bio-hydrauli oil had the roughest surfae also.Signiantly, however, the bio-hydrauli oil still had the lowest frition oeient. The2% ILC had the most stable urve, whih is an indiation of keeping the same onditionsof frition. In the ase of the 10 % LC, there was a ontinuous derease in the fritionoeient. Bak to LVDT urve, it also behaved in an almost stable manner, in terms975.4. Conlusionof the wear. Thus, the ontinuing wear or inreasing ontat area ould be responsiblefor this behavior.Figure 5.13: Frition oeient Versus time, Pin-on-disk testsTable 5.5: Frition oeient for pin-on-disk testsLubriant Minimum COF Maximum COF Average COF1 Bio-hydrauli 0.052 0.095 0.0722 10% LC 0.132 0.169 0.1533 2% ILC 0.104 0.133 0.1235.4 ConlusionThe ioni liquid rystals improved the wear resistane property of the oil, while the fri-tion went higher. This needs to be investigated further, with more stable and identialontat areas, suh as with a washer on disk setup. In addition, the eet of tem-perature, the perentage of the additives, and the type of rubbing oupling deserve to985.4. Conlusionbe investigated. The 10 % LC did not have a positive impat on the oil. Although,it is known from the literature that it has good surfatant properties, espeially withsteel. This raised many questions about its ompatibility and ompetitivity with bio-oilmoleules. Realling from the rheology haraterization (3.8, 3.10), adding holesterylhloride to bio-hydrauli oil dereased the G' prime slightly, whih ould be interpretedas showing that its moleules were not inompatible with bio-hydrauli oil moleules. Inaddition, the investigation into the surfatant behavior of 2%ILC showed less inueneon the bulk properties, whih ould be interpreted as showing that the bio-hydrauli oilhad a thiker boundary regime.99Chapter 6Conlusion and Future Work6.1 AhievementsTo our awareness, the presented researh is the most extended study on the rheologialharaterization of low visosity bio-lubriants. This is the rst study to investigatethe eets of the geometry material on the rheologial response of the tested material,as well as to present rheometry and thermal analyses as tehniques for studying thesurfae ativities. More redible equations to t the visosities versus temperature wereproposed. Using the rotary rheometer to apply a broad shear rate range on low visosityuids was demonstrated. Furthermore, the visoelasti and liquid rystal nature of thebio-lubriants were revealed. Exellent lubriity of bio-lubriant, and the impats ofliquid rystal additives on it were investigated.6.2 HypothesesFirst hypothesis: The tested bio-lubriants behave like liquid rystals.Argument:? It has a signiant elasti modulus (G') even the moleular weight it is not thatlarge? G' grows with time.1006.2. Hypotheses? G' is deayed by heating and shearing.? G' with respet to angular frequeny and visosity with respet to shear rate.behave in similar manner to a holesteri liquid rystal? The polarized light mirosope revealed optial ativities aording to hanges intemperature and shear rate.? Compared with mineral oil, anola oil has larger moleules that are highly polar.? Crystalization or sedimentation are known phenomena in raw anola oil.? The thermal analysis showed more events rather than melting and boiling points,and some of them at relatively high temperatures.Disussion: The visoelastiity of tested bio-oil annot be due to the moleular stru-ture only; it is smaller than that. Also, the growing G' annot be due to oxidation,evaporation, or any other hemial reation, beause it is reoverable. To see the stru-ture of the oil requires a mirosope with enough magniation and suitable onditionsto allow the rystals to grow. However, we expet the existene of more than one phase,whih makes the ase more omplex.Seond hypothesis: The extended Self Assembled Monolyayer (SAM) intothe bio-oil has a thikness muh larger than the moleular length of a fewnanometers.Argument:? The extended SAM aeted the bulk properties? There was a signiant dierene in G' between a 0.4mm gap and a 0.2mm gap,whih means that the dimensions on suh a sale make a dierene.1016.2. HypothesesDisussion: It is known that materials that have surfae ativity aet the surfaetension [96?, surfae tension ould aet the rheometry results. However, what happenedin the bio-oil is more than surfae tension, as the geometry surfae that was in ontatwith the oil gave dierent results than the surfae that was leaned thoroughly.Third hypothesis: the substrate material aets the mirostruture of thebio-lubriant .Argument:? Geometry material aeted G'.? The eet of geometry materials maximized at narrow gaps.? Adding ILC to bio-hydrauli oil diminished the eets of the subtrate.Disussion: Previous results indiated a reation between the surfae and the bio-hydrauli oil. The ILC is a strong surfatant, therefore we suspet that it oupied thebio-hydrauli oil plae on the surfae. The self-assembled mono layer did not extendthis time, so the eet of the gap was diminished. Even though the wear resistanewas improved by adding ILC, the pure bio-hydrauli oil kept the lowest frition fator.The assumption of an extended self-assembled mono layer ould explain that. In otherwords, while the ILC produed a stronger SAM , the pure bio-hydrauli oil had a muhthiker one.1026.2. HypothesesFourth hypothesis: The surfatant behavior ould be studied using rheome-try and TAArgument:? In rheometry, a type of oupling between the tested material and the geometrymaterial aeted the results , whih we attributed to the surfae ativity.? The SAOS result with arefully leaned geometry diered from the result withreused geometry that only wiped out by paper towel.? In TA, the more surfae area with respet to the mass hanged the behavior.Disussion: The relative exposed surfae area of the samples in DSC ampoules tothe air and metalli walls inreased with a derease in the mass sample. However, theeet annot be due to the reation with air beause it happened at both low andhigh temperatures; it maximized in some areas, and beame ineetive in others. Usingrheometry to study the surfae ativity will have an advantage in the eld of lubriation,due to ontrol of the testing onditions suh as temperature, shear, and the posibilityto apply an eletri eld or UV exposition.Fifth hypothesis: the bio-oil has superior lubriity to the mineral oil.Argument:? Aording to the Four-ball test, the sar made with presene of bio-hydrauli oilwas 15% less than that sare with presene of mineral hydrauli oil.? Aording to the Four-ball test, the oeient of frition of the bio-hydrauli oilis 35% less than that of the mineral hydrauli oil.1036.3. Questions RaisedDisussion: The real sar produed by the four-ball test with the bio-hydrauli oilould be muh less if it was took into aount only the area where the erosion wasonentrated .However, the oeient of frition in the ase of the bio-hydrauli oil wasstill the lower. This onrms the superior lubriity of bio-hydrauli oil over mineral oil.Sixth hypothesis: Ioni liquid rystals (ILC)improved the lubriity resistaneof bio-oil.Argument:? Aording to the pin-on-disk tests, 2% of the ILCs dereased the wear on the ball,the size of the sar on the disk and the worn volume from the disk.? The sample that had 2% ILC had the most stable oeient of frition based onthe pin-on-disk test.Disussion: It is not lear why the ILC improved the wear resistane, but the purebio-hydrauli oil kept the lowest oeient of frition. Aording to the rheologial har-aterization work, we an assume that the ILC provided a stronger and faster formattedSAM. Still the pure bio-lubriant had a thiker layer. Further investigation into theeets of the normal fore and time ould onrm or invalidate this assumption.6.3 Questions Raised? If the bio-lubriant has dierent rystalline phases aording to temperature, whatis the tribologial performane of eah rystalline phase?? If the bio-lubriant has dierent rystalline phases at the same temperature, howan they be studied separately?1046.4. Conlusion? If the SAM of a bio-lubriant takes time to build up, how is this reeted in thetribologial performane?? If the rystalline behavior omes from dierent ombinations in the bio-lubriant,what is the inuene of every omponent on the tribologial performane?6.4 Conlusion? A rotary rheometer an be used to perform SAOS and wide abroad shear tests onlow visous liquids under proper setups.? Compared with tested mineral hydrauli oil, tested bio-lubriants had more stablevisosities over temperature.? A double exponential equation an represent the hanges in the visosity againstthe temperature, aurately, under the tested domain.? The yield stress in the bio-hain oil was measured in temperatures lower than 20oC. The eet of temperature history faded by time.? The bio-hydrauli oil has a harateristi urve (G' vs. frequeny) similar to aholesteri liquid rystals. G' has a plateau region under 1 Hz and intersetedwith G at a lower frequeny, whih is an indiation of solid like behavior.? Bio-hydrauli G' time dependene was investigated. In ontrast, engine oil did notshow any time dependene.? Gap size aeted the rheologial behavior of bio-lubriants.? The surfae ativities of bio-hydrauli oil aeted the rheometry results.1056.5. Future Work? The G' of bio-hydrauli oil, whih indiates the mirostruture, was deayed byshear and reovered by time.? Compressed CO2 dereased the visosity of bio-hydrauli oil while ompressed N2inreased it under the tested range of tested pressures.? Some optial ativities of bio-lubriants, aording to shear and temperature hanges,were able to be observed using a polarized mirosope.? Some transition points were noted on the DSC urves of the bio-lubriants whihould denote rystallization, or represent signatures of ertain ompositions in thebio-lubriant.? A orrelation between the DSC and SAOS results was noted.? The mass size aeted the DSC results and denoted to the surfae ativities? Bio-hydrauli oil exhibited better tribology performane when ompared withtested mineral hydrauli oil, aording to the four-ball test.? Aording to the pin-on-disk test, and under the applied onditions, adding 2%of the tested ILC improved the wear resistane property of the bio-hydrauli oil,while the pure bio-lubriant kept the lowest oeient of frition.6.5 Future Work6.5.1 RheometerThe rheometer has advaned ontrol software, very sensitive sensors, and very goodontrol on the test onditions. It ould be modied and improved to beome an ad-vaned general testing station. (rheometer, nano-tribometer, tensiometer, mirosopyrheometer)1066.5. Future Work? We were limited in our ability to haraterize diluted and low visous solutions.Improving the methodology will reet positively in the results. Further develop-ment of the geometries used to address spei appliations is still needed. Somespei-use geometries are already in use, suh as: multi wall one, and plate andylinder and up.? Use some alternatives to an eletri motor to perform high frequeny motions, suhas the piezoeletri ell [97?? As expeted, using a polarized light mirosope with high apabilities will allowobserving the rystalline phases more losely. An ordinary onverted mirosopeould be attahed to the rheometer, GEMINI brand [98, 99?.? With hange in design of the geometry the rheometer an be used as nano-tribometer in order to get more preise measurements on the frition[100?.? Surfae tension is a meaningful indiation when studying surfae ativities; it isnot diult to use the rheometer as a tensiometer and get the benet of its preiseontrol.6.5.2 TribometerA number of instruments and failities an be added to the tribometer to enhane itsperformane and apabilities.? A ommerial irulating bath an be used to ontrol test temperatures on thetribometer? Using a pneumati or eletri atuator to apply normal fore instead of deadweights, and using air bearings for the rotating table will redue the vibrations.1076.5. Future Work? Using a miro ohmmeter to measure the eletri resistane between the ball andthe disk will help us understand the development of SAM and the ontat area.? Installing a digital mirosope to observe the sar on the disk will help to observeit over time.6.5.3 Mathematial ModelThere is a need to improve the mathematial model, speially for the lubriation prob-lems; this an be done either by validating and modifying known visoelasti and liquidrystal onstitutive equations, or using Moleular dynamis to simulate the lubriatingproblem, espeially within miro and Nano gaps.6.5.4 ExperimentsEndless numbers of experiments an be done to answer the questions were raised, under-stand the bio-lubriant better, and to develop and optimize new produts. Furthermore,formatted SAM on the surfaes an be examined using X ray mirosopy or atomi foremirosopy. Dierent ouplings of lubriants and rubbing surfaes under a matrix ofonditions ould be tested. Testing the same mass samples of bio-lubriant with dier-ent ontat areas (oil/metal) in the DSC will onrm the measurements of the surfaeativity using thermal analysis.108Bibliography[1? 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Tri-bology International 46, 215224.120Appendix ASurfae TensionThe apparatus that have been usedFisher Sienti ( Manual Model 20 Surfae Tensiometer)Surfae tension of dierent oils121Appendix A. Surfae Tensionsurfae tension versus LCs onentration122Appendix BDensityThe apparatus that have been usedpreision sale, AND-E5Density of tested oilsLubriant Density at 23oC (kg/l) +/- 0.5%1 Mineral hydrauli oil 0.855992 Bio-hydrauli oil 0.91093 Bio-gear oil 0.913014 Bio-hain saw oil 0.911955 Engine oil 0.87422123Appendix CThermal ExpansionThe apparatus that have been usedIt was assembled in the labDensity of water versus temperature ( alibration)124Appendix C. Thermal ExpansionDensity of tested oils versus temperatureCoeient of Thermal Expansionlubriant Thermal expansion oeient X 10?61 Mineral hydrauli oil 7562 Bio-hydrauli oil 7463 Bio-gear oil 6414 Bio-hain saw oil 756125

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