Solvent-dependent thermochemistry and volumetric change upon swelling of an organosilica material*

Swellable organically modified silica (SOMS) is a mesoporous cross-linked polysilsesquioxane that rapidly adsorbs organic solvents with a simultaneous increase in its volume. The swelling likely originates from the solvent-induced release of matrix tension and therefore should be governed by solvent-solid interactions at surface interfaces. This mechanistic model is supported by empirical relationships between the swelling of SOMS and the nature of the solvent that induces the swelling. Calorimetric experiments establish that the enthalpy change associated with the swelling of SOMS differs in magnitude according to the identity of the solvent. The volumetric expansion of SOMS upon swelling likewise varies with the type of solvent employed. Efforts are underway to relate these observations to the Hildebrand and/or Hansen solubility parameters of the solvents and thus establish those parameters for SOMS itself. Predictive information about the selective adsorption of different substrates by SOMS enhances its potential for biological and environmental applications.