Control of Polystyrene Film Dewetting Through sulfonation and Metal Complexation
The dewetting of low molecular weight sulfonated polystyrene ionomers (SPS) on inorganic silicon oxide substrates is compared with unmodified polystyrene (PS, Mw = 4000) using a combination of X-ray reflectivity, optical and atomic force microscopy. The amounts of sulfonate group and metal counterion (Li+, Zn2+) were both varied in our study. Unlike unmodified PS, which readily dewets the substrate, a strong inhibition of dewetting occurs for low sulfonation (2.3 mol %), and no apparent dewetting was found for high sulfonation (≥7 mol %). For ZnSPS, dewetting was not observed in any of the films, even for those with very low sulfonation. Comparison with bulk rheological data suggests that inter- and intramolecular ionomer complexation may be important in retarding the dewetting process (a nonequilibrium effect), in addition to an increased wettability arising from long-range electrostatic polymer−surface interactions.