Thermolytic Grafting of Polystyrene to Porous Silicon

Inert-atmosphere thermolysis of polystyrene, preloaded into a porous silicon (pSi) template, generates a composite in which styrenic fragments are chemically grafted via Si C bonds to the surface of the pore walls. The quantity of styrenic material in the pores, and thus the final porosity of the composites, is controlled by the amount of polystyrene initially loaded into the pSi host and the time and temperature of thermolysis. For a host template with a porosity of 64 +/- 1%, the porosity of the resulting composite can be varied from 10 to 50%. The composites are significantly more hydrophobic than bulk polystyrene, displaying water contact angles ranging from 110 to 138 degrees compared to a value of 89 for a pure polystyrene film. The contact angle follows the Cassie rule for porosity values up to 40%, increasing with increasing porosity. For composite porosity values >40%, the contact angle is observed to decrease, and this correlates with increasing silicon oxide content and a decrease in hydrophobicity. The stability of the grafted composite material in aqueous base (>pH 12) is enhanced with increasing styrenic content.