Displacement of hydrophilic colloids from particle interfaces

Abstract

AbstractThe viscosity increase observed when hydrophilic colloids are added to latex/pigment systems indicates strong interaction between particles and macromolecules. The interaction is caused by partial adsorption of the macromolecule with a segment free to expand to a nearby particle to form a rigid network. Attempts were made to displace macromolecules from PVAc copolymer and pigment particles. Displacement of the hydrophilic colloid from the particles into the water phase reduced shear stress as demonstrated by flow curves obtained with the Haake Rotovisco. Rheological measurements with the latex serums obtained by ultracentrifuging and reconstruction of the latex aqueous phases confirmed that the abnormal viscosity increase in the latex is caused by link formation. Nonionic surfactants are amphipathically adsorbed at the particle interface and the macromolecules appear to hydrogen bond to the surfactant hydrophile. Segments of the macromolecules remain free, however, to project into the water phase and form linkages. Post‐addition of anionic surfactants from an homologous series produced marked rheological changes in latex/pigment systems. The disarrayed existence of the macromolecules in the water phase produces flow curves that are consistent with those of the hydrophilic colloid dissolved in water.