Aggregation behavior of Na-neutralized styrene-ran-methacrylic acid copolymers in aqueous solution

The aggregation behavior of un-neutralized, partly and fully Na-neutralized poly(styrene-ran-methacrylic acid) copolymers in aqueous solution was investigated using a SEM technique. It was observed that the un-neutralized copolymer formed spherical particles on the Si wafer, and the average size of particles was ca. 160 nm. The particle sizes did not change much with acid content. Upon the neutralization of the acid groups of the copolymer with NaOH, the copolymer became more hydrophilic, leading to the formation of network-like feature consisting of much smaller particles (< 50 nm), compared to those of the acid copolymers. With increasing ionization, the boundary of the particles forming networks faded away, implying the formation of tubular structures.