Aqueous solution diffusion in hydrophobic nanoporous thin-film glasses

We demonstrate that diffusion of aqueous buffered solutions into strongly hydrophobic nanoporous methyl silsesquioxane glass films can occur without the application of external pressure. The organic component of these glasses in the form of methyl groups imparts the strong hydrophobicity and perception that they are impervious to the ingress of aqueous solutions by capillary action or diffusion. The presence of small concentrations of organic buffering agents in buffered solutions appears to facilitate the diffusion. The diffusion distance followed a square root of time dependence characteristic of Fick's Law. The diffusion coefficients varied markedly with the concentration of buffering agents, solution pH, and temperature. Similar effects were not observed for nonbuffered solutions that exhibited no detectable diffusion. Likely mechanisms responsible for the observed behavior are proposed. © 2007 Materials Research Society.