The Effect of the Co-Solvent on the Aerogel Formation Directly in Supercritical CO2 Medium

A series of flexible hydrophobic siloxane aerogels were obtained by the hydrothiolation reaction in supercritical CO2 medium in the presence of a co-solvent. The effect of the co-solvent nature on the aerogel morphology and physico-mechanical properties were studied. n-Pentane, a propane/n-butane mixture, CH2Cl2, dimethyl ether (DME) and 1,1,2-trichloro-1,2,2-trifluoro-ethane were used as the co-solvents. The morphology of aerogel particles was studied by SEM. In the case of n-pentane, propane/n-butane mixture, CH2Cl2, or DME as the co-solvents, aerogels with a density of 0.18-0.21 g/cm(3) and an average particle size of 0.15-5.35 mu m were obtained. Depending on the morphology, the mechanical properties of aerogels change in the range of 0.2-0.75 MPa (Young's modulus), 38-68 % (compressibility) and 0.11-0.42 MPa (stress rupture). In the case of 1,1,2-trichloro-1,2,2-trifluoro-ethane as the co-solvent, the aerogel with an inhomogeneous structure was obtained. All the aerogels studied have a large water contact angle in the range of 142 degrees-151 degrees.