Mechanical properties of mesoporous silica thin films: Effect of the surfactant removal processes

Abstract

Mechanical properties including hardness and Young's modulus of ordered mesostructured silica thin films are characterized by nanoindentation measurements. PE6800 and CTAB are used as templating agents. Emphasis is given on the effect of the template removal by thermal treatment, solvent extraction or UV-Ozone irradiation. The mechanical properties of the film are intimately correlated to the microstructure of the silica network and the film porosity as studied by IR, X-ray diffraction and N 2 adsorption. Particularly, the position and shape of the longitudinal optic mode of the Si–O–Si asymmetric stretch are correlated to the mechanical response as a function of the treatments. A contrasted behaviour is observed between PE6800 templated films which present low initial condensation state and high network contraction after post-synthesis treatments, and CTAB templated films which exhibit higher initial silica condensation degree but lower compressibility after template removal. These distinct behaviours are correlated to the strengthening of the silica structure and the decrease of the film porosity during template removal, which evolve differently according to the nature of the template and the template removal processing.