UNSUPPORTED SIO2-BASED ORGANIC-INORGANIC MEMBRANES .2. SURFACE-FEATURES AND GAS PERMEATION

Gas permeation of unsupported hybrid membranes, obtained by co-hydroly sis of various Si(OEt)(4)/MeSi(OEt)(3)(TEOS/MTES) mixtures, is studied with Ar, He and N-2. The separation performance of these hybrid membr anes is higher than for pure SiO2 sol-gel derived membranes and depend s on chemical composition: a considerable increase in separation facto r alpha(He/N-2) is found as the amount of MTES increases; moreover, ga s permeability decreases with increasing organic modification of the n etwork. Membrane characterization is performed by N-2 adsorption-desor ption measurements and low-temperature differential scanning calorimet ry (DSC) and dynamic contact angle (DCA) analyses. Data are related to chemical composition, affecting both the chemical nature of the surfa ce and gas permeation. Results indicate that gas permeation through hy brid membranes may favour the Knudsen flow model or surface diffusion mechanism, depending on the TEOS/MTES ratio.