Influence of physico-chemical parameters on the surface photopatterning in hybrid sol-gel glasses

Sol-gel process is for more than one decade an interesting way to synthesize inorganic-organic composites under a soft chemistry route. Recently a process for the fabrication of self-developing diffractive optical elements has been developed. The inorganic part of the molecule was an alkoxysilane that reacted via hydrolysis and condensation reactions at room temperature, thus leading to a gel. The mild conditions under which the inorganic part of the material was prepared are compatible with the presence of an organic moiety, a methacrylate function. The organic network was produced via spatially controlled UV illumination using amplitude masks. Surface relief gratings were obtained via this photochemical step ; generation of relief resulted from mass-transfer by diffusion and gradient of surface free energy. No etching process was required. Although the hybrid sol-gel material was assumed to perform along the same lines as the one involving all-organic photopolymers, the influence of the inorganic moieties on the photopolymerization of the methacrylate function remained unknown. Characteristics of the photopolymerization process taking place in hybrid sol-gel materials were investigated by UV and FTIR spectroscopies. Besides the study of the organic network, NMR investigations led information relative to the inorganic network formation during the sol ageing. The whole results provide insights into the influence of the temperature during the photochemical step. Relief gratings generated under various conditions and for a large scale of spatial frequencies are presented. Sinusoidal to almost binary profiles were obtained in a one-step process.