Auto-organisation in silica-based organic-inorganic gels obtained by sol-gel process

A new type of hybrid material is prepared through sol-gel processing by the polycondensation of (MeO)(3)Si-R-Si(OMe)(3) units containing a rigid organic anisotropic group R. The hybrid covalently bounded organic-inorganic gel shows an unexpected structural birefringence Deltan(Deltan = 2 x 10(-3)). This birefringence is induced by a strain field anisotropy during gel aging as revealed by simultaneous dynamic light scattering and birefringence measurements. To better address the role of the strain field, we use a free interface sol-gel/air to control strain anisotropy and to measure the gel optical axis and its birefringence. We find that the birefringence is associated to a long-range orientational order of organic moieties induced by the strain anisotropy during the gel aging.