Properties of Nano-Hybrid Sol-Gel Coating Films Synthesized with Colloidal Silica and Organoalkoxy Silanes

Three kinds of colloidal silica (CS)/silane sol were prepared. Sols are involved with the kinds of silane with different organic group. Methyltrimethoxysilane (MTMS) has the three methoxy groups and a methyl group. γ-Glycidoxypropyltrimethoxysilane (GTMS) has the three methoxy groups and a bulky epoxy group. GTMS was added to two sols with different amount. When sol reacted for 10 days, viscosity increased dramatically. Trasnmittance of sols reacted for 10 days decreased rapidly, too. It indicated the stability of sol degraded. Sol-gel coating films were formed on glass substrate using spin coating procedure with reaction time for 10 days. Coating films were flat and transparent without cracking. CS/MTMS coating films showed high contact angle. When large amount of GTMS was added, contact angle decreased due to its epoxy group. No thermal degradation of CS/MTMS coating film occurred up to 600 oC. CS/MTMS/GTMS coating film degraded at 400 oC for decomposition of epoxy group which has long organic chain which easily degraded by the thermal shock.