Some aspects of colloidal polymers: Solvent structure originated interactions

Abstract

The coagulation of some aqueous latex dispersions has been studied. Type-1-dispersions were made by emulsifier free emulsion polymerization of styrene and stabilized by anionic or cationic groups at the surface of the latex particles. Because of charge stabilization a sufficiently large amount of electrolyte forced the particles to coagulate by double-layer compression. The value of the critical coagulation concentration for monovalent counter ions is intimately connected to the water structure and to the kind of particle surface groups. The interaction of ions with the boundary region developed between the particle and the aqueous dispersion medium is also influenced by temperature and by the addition of organic molecules which can interfere with the microstructure of the solid-solution interface. The impact of a direct change of the particle surface characteristics on stability is illustrated for several type-2-latices which were synthesized by seed and feed copolymerization of styrene and glycidyl methacrylate. Particles with different surface structure were derived from the same stock dispersion by the nucleophilic addition of D-glucamine and taurine to the reactive epoxy group at the particle surface. Differences in the critical coagulation concentration may then be attributed to changes in the structure of the latex surface. The alteration of the boundary region separating the latex particles from the dispersion medium is well reflected by kinetic and electrophoretic experiments.