The characterization of monodisperse polystyrene latices

Four monodisperse polystyrene latices, containing particles of diameter ca. 2400 Å, were prepared using hydrogen peroxide and potassium persulfate as initiators and sodium dodecanoate, sodium mono‐dodecyl phosphate, and dodecylamine hydrochloride as emulsifiers. These latices were characterized by electron microscopy, gas adsorption, and microelectrophoresis. The results obtained by the first two techniques indicated that the particles were essentially nonporous rigid spheres. Electrokinetic procedures were used to characterize the ionogenic groups on the latex particles. In addition to the emulsifier molecules, other groups, namely carboxylic acid groups, were found to be present on all of the latices, irrespective of the nature of the initiator or umulsifier used to produce them, Electrophoresis also revealed that the emulsifiers could be removed from the latex dispersions by dialysis, leaving systems with these carboxyl groups as an integral part of the particle surfaces. By electrokinetics, the surface pK value of these unknown acid groups was 4.64. It was also established by radiochemical methods, combined with microelectrophoresis, that sodium dodecanoate was removable by dialysis from polystyrene latices. Before dialysis the concentration of the free emulsifier was below the critical micelle concentration. The latter experiments also suggested that the construction of adsorption isotherms from electrokinetic data is of doubtful validity. The integral carboxyl groups were probably produced by polymer oxidation during polymerization.