Porosity and mechanical properties of mesoporous thin films assessed by environmental ellipsometric porosimetry

Mesoordered silica thin films with cubic structures were prepared by evaporation induced self-assembly (EISA) with two types of structuring agent (CTAB and block copolymer F127). A complete and accurate description of these films was obtained by combining 2D-SAXS analyses, variable angle spectroscopic ellipsometry, and a specially designed environmental ellipsometric porosimetry (EEP) experiment. The EEP analysis is rapid and cheap and operates at ambient pressure and temperature. This latter experiment was performed with water and produced a set of water adsorption-desorption isotherms. A modified Kelvin equation, coupled with a modelisation of pores contraction, enabled the determination of the structural parameters of films porous networks: ellipsoidal pore diameters, porous volume, and surface area. Young moduli of films in the direction perpendicular to the substrates were calculated from these parameters.