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UBC Theses and Dissertations

Rheology and dye adsorption of surfactant-cellulose nanocrystal complexes Ranjbar, Damoon


The adaptability of Cellulose Nanocrystal (CNC) with reference to two of its major applications, namely viscosity modification in complex fluids and dye adsorption, is investigated. In the context of viscosity enhancement, the interaction of CNCs with two ionic surfactants, namely sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB), has been explored in this study. The effect of CTAB and SDS on surface charge of CNCs is analyzed and coupled with the rheological properties in order to investigate the mechanisms in CNC/surfactant and CNC/CNC interactions. It was found that both surfactants result in gelation of chiral nematic CNC suspensions by setting the stage for establishment of crosslinks between individual CNCs. In the case of CTAB, a gradual increase in the viscoelastic moduli was observed with the concentration of surfactant implying the induction of dominant attractive forces between CNCs by surfactant molecules. However, the presence of SDS results in the emergence of both attractive and repulsive forces whose dominance controls the viscoelastic properties. In the context of dye adsorption, a CNC based adsorbent was first synthesized by modifying the pristine CNC with various amounts of CTAB and consequently was used to study the adsorption behavior of Congo red (CR) in aqueous medium. The interaction of CTAB with CNC, and potential alterations on the chemical and physical structure of CNC was studied. The synthesized adsorbent, a modified cellulose nanocrystal (MCNC), was characterized using Fourier transform infrared (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and zeta potential analysis. The amount of surfactant used for modification exhibited an optimum at which the adsorption capacity was shown a weak maximum. Furthermore, it was found that the amount of surfactant affects the CR-MCNC interactions and determines the mechanisms of adsorption. Characterization of the adsorbent, before and after adsorption, coupled with kinetics and isotherm studies implied electrostatic attraction, hydrogen bonding, and hydrophobic attraction as the main mechanisms of adsorption. Thermodynamic studies on the system suggested that the adsorption process is spontaneous and exothermic. Finally, stability analysis in aqueous environment revealed that the adsorbent is highly stable and retains its original adsorption capacity after successive dialysis cycles.

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