Interactions of grafted polymer brushes measured by atomic force microscopy
department or school: Science, Faculty of
department or school: Chemistry, Department of
data provider: DSpace
degree campus: UBCV
creator: Goodman, Diane
issued: 2009-12-01T17:52:58Z
issued: 2004
related degree: Doctor of Philosophy - PhD
degree grantor: University of British Columbia
description: The interaction forces exerted by latex particles bearing densely grafted polymer layers of poly(N,N-dimethylacrylamide) (PDMA), poly(methoxyethylacrylamide) (PMEA), and poly(N-isopropylacrylamide) (PNIPAM) in aqueous media (good solvent) were investigated by atomic force microscopy (AFM). The molecular weight (Mn), grafting density (σ), and polydispersity (PDI) of the brushes were determined by gel permeation chromatography (GPC) and multi-angle laser light scattering after cleaving the polymer from the latex surface by hydrolysis. The hydrodynamic thicknesses were measured by dynamic light scattering and were comparable to the equilibrium thicknesses measured by AFM. The values were also similar to those predicted by a numerical self-consistent mean field model after scaling the dimensions and flexibility of the lattice chains using experimentally determined parameters. Force profiles of PDMA (0.017 nm-2 ≤ σ ≤0.17 nm-2) and PMEA (σ = 0.054 nm-2) brushes were purely repulsive upon compression, with forces increasing with Mn and σ, as expected, due to excluded volume interactions. At a sufficiently low grafting density (σ = 0.012 nm-2), PDMA exhibited a long-range exponentially increasing attractive force which was attributed to bridging. A bridging force was detected in the PNIPAM brush at σ = 0.037 nm-2; at this density the PDMA brush force profile was purely repulsive. Bridging was therefore found to depend on grafting density as well as on the nature of the monomer. The Mn and PDI of the polymer brushes were determined by two independent force techniques, the suitability of which depended on the interaction of the polymer with the AFM tip. For non-adsorbing polymers, the distribution of contour lengths measured by stretching individual chains was compared with GPC distributions for surfaces with different grafting densities. The force technique was appropriate for dense brushes in good solvent but underestimated the Mn for surfaces with low σ (mushroom regime). …
aggregated CHO: https://circle.library.ubc.ca/rest/handle/2429/16020
extent: 14701727 bytes
format: application/pdf
note: INTERACTIONS OF GRAFTED P O L Y M E R BRUSHES M E A S U R E D B Y ATOMIC FORCE MICROSCOPY by DIANE G O O D M A N B.Sc. (Chemistry) McGil l University, 1997 A THESIS SUBMITTED IN PARTIAL F U L F I L L M E N T OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE F A C U L T Y OF G R A D U A T E STUDIES (Department of Chemistry ) We accept this thesis as conforming To the required standard THE UNIVERSITY OF BRITISH C O L U M B I A July, 2004 © Diane Goodman, 2004 Abstract The interaction forces exerted by latex particles bearing densely grafted polymer layers of poly(N,N-dimethylacrylamide) (PDMA), poly(methoxyethylacrylamide) (PMEA), and poly(N-isopropylacrylamide) (PNIPAM) in aqueous media (good solvent) were investigated by atomic force microscopy (AFM). The molecular weight (M n ), grafting density (a), and polydispersity (PDI) of the brushes were determined by gel permeation chromatography (GPC) and multi-angle laser light scattering after cleaving the polymer from the latex surface by hydrolysis. The hydrodynamic thicknesses were measured by dynamic light scattering and were comparable to the equilibrium thicknesses measured by A F M . The values were also similar to those predicted by a numerical self-consistent mean field model after scaling the dimensions and flexibility of the lattice chains using experimentally determined parameters. Force profiles of P D M A (0.017 nm"2 < a < 0.17 run"2) and P M E A (a = 0.054 nm" ) brushes were purely repulsive upon compression, with forces increasing with M n and o, as expected, due to excluded volume interactions. At a sufficiently low grafting density (a = 0.012 nm" ), P D M A exhibited a long-range exponentially increasing attractive force which was attributed to bridging. A bridging force was detected in the PNIPAM brush at a = 0.037 nm"2; at this density the P D M A brush force profile was purely repulsive. Bridging was therefore found to depend on grafting density as well as on the nature of the monomer…
has type: Thesis/Dissertation
date issued: 2004-11
is shown at: 10.14288/1.0061189
language: eng
degree discipline: Chemistry
provider: Vancouver : University of British Columbia Library
publisher: University of British Columbia
rights: For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.
scholar level: Graduate
type: Text
identifier URI: http://hdl.handle.net/2429/16020