Anisotropic and Reversible Deformation of Mesopores and Mesostructures in Silica-Based Films under Mechanical Stimuli toward Adaptive Optical Components

Deformation of the mesostructures in surfactant/silica hybrid films and mesoporous silica films prepared on bulky elastomeric substrates is investigated by compressing the substrates along an in-plane direction of the films. The mesostructure in the surfactant/silica hybrid film consists of organized micelles and a silica matrix. The micelles are removed in the mesoporous silica films to leave mesopores. A grazing-incidence small-angle X-ray scattering investigation reveals that the mesostructures with C2mm symmetry anisotropically change under a compressive strain of 6% in both films; shrinkage of the lattice parameters is along the direction of compression and extension in the normal direction. Deformation is reversible below a strain as high as 6%. Anisotropic deformation of the mesostructures results in an anisotropic change of the refractive indices normal and parallel to the direction of the compression. Compression of the surfactant/silica hybrid film induces a decrease of the refractive index parallel to the surface and an increase normal to the surface on the order of 10–3, while an opposite result is observed for the mesoporous silica film. The present finding gives us fundamental insight into the development of adaptive optical components for sensing, attenuation, switching, modulation, shutters, filters, and others in soft-material-based devices.