Swelling thermochemistry and temperature-dependent adsorption of swellable organically modified silica

Swellable organically modified silica (SOMS) is a crosslinked polysilsesquioxane network that swells upon contact with organic solvents. Basic performance parameters such as the volume of swelling and total adsorption capacity are identical among a range of solvents at room temperature. Constant-pressure calorimetry demonstrates that the enthalpy of swelling varies, both in magnitude and mathematical sign, with the identity of the organic solvent. No clear trend exists between the enthalpy of swelling and the polarity or viscosity of the solvent causing the swelling. A series of variable-temperature experiments establish a slight temperature dependence of the enthalpy of swelling, with higher initial temperatures causing the acetone-induced enthalpy of swelling to decrease in magnitude (become less exothermic). The solvent adsorption capacity of SOMS also changes with temperature, albeit in different ways. At higher initial temperatures the adsorption capacity of the material sold under the trade name Osorb decreases, but increases for the less-crosslinked material known as Cyclasorb. Our calorimetry experiments build a foundation from which to characterize the thermodynamics of swelling SOMS for applications in actuators and sensors.