Effects of Molecular Weights of Sulfonated Polystyrene Ionomers on the Formation of Stable Colloidal Particles in Tetrahydrofuran/Water (1/99) Mixture

Abstract

The effects of the molecular weights (MWs) of sulfonated polystyrene copolymers on the colloidal particle sizes and the size distributions were investigated. It was found that the size of colloidal particle of acid copolymer of relatively low MW, being largest in comparison with higher MW sample, decreased strongly and then remained constant at ca. 11 nm upon dilution. These findings implied that at relatively high concentrations the colloids aggregated together due to the interactions between particles having relatively non-polar surface and that the colloids might contain more than one polymer chain. In the cases of copolymers of high MWs, the colloid sizes did not change much with the solution concentration, but the particle size of the higher MW copolymer was slightly larger than that of the lower MW sample. This was understood; the higher MW copolymer, the longer polymer chain, and the larger colloid. The size of the ionomeric colloids was found to increase slightly upon dilution, which was due to the repulsion of ionic groups on the surface. As expected, the size of the particles of the ionomers showed a similar trend found in the acid samples.