Surfactant-free syndiotactic polystyrene aerogel foams via Pickering emulsion

Abstract

This work investigates fabrication of aerogel foams from syndiotactic polystyrene (sPS) using silica-based Pickering emulsion method. A large fraction of micrometer size voids (macrovoids) is created inside porous thermo-reversible sPS gels by dispersing water droplets without the use of surfactants before gelation of sPS solution. The method used in this work alleviates two critical concerns of surfactant-stabilized emulsion templating method, namely the sensitivity of emulsion stability to temperature and the difficulty of removing the surfactants from aerogel foams. Hydrophobic silica particles of diameter 50–70 nm are used to stabilize Pickering emulsion of micrometer size water droplets in emulsions of sPS solution in toluene at 110 °C. Emulsion stability shows weak dependence on temperature and on water volume fraction. The sPS chains form thermo-reversible gels when cooled to room temperature and lock the water droplets inside the gel. The aerogel foams, recovered via supercritical drying, show high porosity and coexisting macrovoids and macropores. The most probable macrovoid size varies in the range of 50–600 μm and is strongly dependent on water volume fraction. The silica particles are found localized on macrovoid surfaces.