Competitive adsorption of uncharged macromolecules from homopolymer-copolymer mixtures

Individual adsorption and simultaneous competitive adsorption of dissolved macromolecules from ternary polymer solutions (two polymers in one solvent), on negatively charged colloidal dispersions were studied. Poly(vinyl alcohol) (PVA), poly(vinyl pyrrolidone) (PVP) homopolymers and poly(vinyl alcohol-co-vinyl acetal, -vinyl propional and -vinyl butyral) copolymers with various acetal contents and chain structure were used in the experiments. The hydrophilic/hydrophobic character of the macromolecules, and also, the preferential adsorption from homopolymer-copolymer mixtures were systematically regulated by changing the chemical structure of the copolymers (acetal content and/or length of side chain). Independent adsorption isotherms for each polymer were determined in individual adsorption of the polymers and also, in simultaneous competitive adsorption of two polymers from mixtures. It was found that both the degree and the order of adsorption preference could be well regulated by changing the copolymer composition. Model calculations concerning a possible distribution of acetal groups in the copolymer chains provided further support to this experience. The hydrodynamic thicknesses of adsorbed polymer layers formed at particle/solution interfaces in individual and competitive adsorption have been measured by photon correlation spectroscopy. The adsorbed layers formed at high surface coverages from certain homopolymer-copolymer mixtures had the same thickness as that of the preferred component in the individual adsorption layer, illustrating that under conditions the weakly adsorbed macromolecules could be displaced completely from the interfaces. (c) 2006 Elsevier B.V. All rights reserved.