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.
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