Methyl modified siloxane melting gels for hydrophobic films

Hybrid melting gels were prepared by a sol-gel process, starting with a mono-substituted siloxane and a di-substituted siloxane. Methyl-modified melting gels were prepared using (a) methyltriethoxysilane (MTES) with dimethyldiethoxysilane (DMDES) and (b) methyltrimethoxysilane (MTMS) together with dimethyldimethoxysilane (DMDMS). The gels with MTES-DMDES were prepared with concentrations between 50-50 and 75-25 mol%. The gels with MTMS-DMDMS were prepared with concentrations between 50-50 and 70-30 mol%. For both systems, the consolidation temperature, after which the melting gel no longer softens, increased with an increase in the amount of the mono-substituted siloxane, increasing from 135 to 160 A degrees C for MTES-DMDES and increasing from 145 to 170 A degrees C for MTMS-DMDMS. Coatings formed on mica substrates were about 1 mm thick, and showed no visible cracks. The surfaces of the coatings were profiled using micro-Raman spectroscopy, which revealed that methyl groups were concentrated at the surfaces of the films. All contact angles measured with water were greater than 90A degrees.