Spacious and mechanically flexible mesoporous silica thin film composed of an open network of interlinked nanoslabs

Transparent and smooth silica thin films with a very high porosity were prepared by linking zeolitic nanoslabs into open mesoporous networks. Calcined films characterized by ellipsometric porosimetry presented pore sizes in the range of 6-18 nm and porosities of 70-90% depending on the temperature of assembly of the nanoslabs in the presence of Pluronic P123 triblock copolymer. The films were disordered according to grazing incidence small angle X-ray scattering and transmission electron microscopy. The most spacious film had a very low refractive index of 1.08 (at 632.8 nm) and exhibited reversible shrinkage of up to 30% of its original thickness upon capillary condensation of adsorbate vapor. The mechanical flexibility of the film was confirmed by the low Young modulus of 0.9 GPa determined by nano-indentation. The full accessibility of the porosity and the convenience for chemical functionalization were demonstrated using Atomic Layer Deposition (ALD) of TiO2 monitored with Rutherford Backscattering Spectroscopy. Using ALD the porosity and mechanical flexibility of the film could be fine tuned.