SYNTHESIS AND SIZE CONTROL OF POLYSTYRENE LATTICES VIA POLYMERIZATION IN MICROEMULSION

This publication describes the controlled synthesis of very fine polystyrene latices with 10 nm < R < 60 nm via polymerization in microemulsion and their characterization by light- and neutron-scattering and electron microscopy. The microemulsions are formed by dispersion of styrene in water, using cetyltrimethylammonium chloride (CTMA) or dodecyltrimethylammonium bromide (DTMA) as surfactants. The size of the resulting particles is controlled only by the ratio of styrene to surfactant. Within a certain range, the relation between stoichiometry and droplet size is described by a simple geometric model. The limited pliability of the surfactant interface results in a minimum droplet size which is obtained at the limit of high surfactant concentrations. These particles, once polymerized, swell homogeneously with additional monomer. The geometric model for droplet size control can be generalized to other nonpolar monomers. By contrast, the polymerization in microemulsion of polar monomers such as methyl methacrylate (MMA) and even copolymerization reactions with MMA become more complex, and the simple model fails. We assume that MMA itself acts as a cosurfactant (self-surfacting system) and diminishes the interface energy in the case of copolymerization with styrene.