Tetraethoxysilane (TEOS) and diethoxydimethylsilane (DEDMS) with ethanol and water were used as starting materials to prepare a gel by the sol-gel method. In order to find the film formation condition of sol, the sol was coated on a slide glass with its viscosity range of 5-10 centipoises and then the thermal stability of Disperse Orange 25 in gel matrix was investigated. The film thickness was ranged from 0.4 to 2 μm by controlling the compositions of starting materials.
The structures and physical properties the of gels were also investigated by measuring the bulk density, nitrogen adsorption and FTIR spectroscopy. The bulk density became lower by the addition of DEDMS, which would be resulted from the methyl group interrupting the shrinkage and the ring formation of DEDMS. From the test of nitrogen adsorption,it was recognized that micropores rather than macropores formed mainly in the gel.
All the sols showed the transition behaviors from Newtonian to shear thinning with the increase in the sol concentration by the vaporization. The transition would be caused by the agglomeration of polysilicate particles.
A nonlinear optical material, Disperse Orange 25, was added to the sol, coated on a ITO glass, and poled during the drying process. The order parameter of DO25 molecules in the gel film was calculated from UV absorbance spectrum as an indirect measure of thermal stability and compared with that in the organic polymer film including the poled DO25 molecules. The order parameter of DO25 molecules in the gel film was diminished more slowly than that in the polymeric film. The order parameter abruptly increased above threshold field strength (7.5 KV). When poling time increased from 40 to 60 min, the absorbance intensity was unchanged. From this result, it was shown that the gelation of sol coated on ITO glass took place before 40 min.