Formation of the Colloidal Particles of Sulfonated Polystyrene Ionomers Neutralized with Either Na(I) or Ba(II) in THF/Water (1/99) Mixture

Abstract

The sizes of colloidal particles in THF/water (1/99 v/v) of the sulfonated polystyrene copolymers containing 2.1, 5.1 and 9.4 mol% of either acidic or ionic repeat units were determined using a dynamic light scattering technique. It was observed that for the acid copolymer containing 2.1 mol% of acidic units the size of the particle and size distribution decreased significantly as the solution concentration decreased from 2.0 x 10(-4) to 5.0 x 10(-6) g/mL. However, when the content of acidic units increased to 5.1 and 9.4 mol%, the size of the particles and size distribution increased slightly with decreasing solution concentrations. It was also found that the neutralization of the acid group with Na(I) induced the slow increase in the diameter of colloidal particles of the ionomers with decreasing solution concentration, and that the size of the colloids decreased with increasing ion contents. Thus, it was suggested that the former and latter findings could be understood using the polyelectrolyte effect and charge density concepts, respectively. For the ionomers neutralized with Ba(II), it was found that the size of the single colloidal particles was similar to that of the Na(I) ionomer. However, the aggregates of the colloids were not easily separated by the ultrasonication. Thus, it was speculated that the Ba(II) cations placed inside the aggregates of hydrophobic environment acted as the links between colloidal particles.