The effect of temperature and catalyst on polycondensation of organic-inorganic hybrid silica derived from mono-substituted trialkoxysilanes using sol-gel method 一置換アルコキシシランからゾルゲル法によって作製された有機-無機複合シリカの縮合における温度と触媒の影響
The effect of temperature and catalyst on polycondensation of organic-inorganic hybrid silica derived from mono-substituted trialkoxysilanes using sol-gel method
Ashraf, Kayesh Mohammad
アシュラフ, カイエッシュ モハマンド
本タイトル (誤植) : The effect of temperature and catalyst on polycondnsation of organic-inorganic hybrid silica derived from mono-substituted trialkoxysilanes using sol-gel method
Organic-inorganic hybrid silica derived from mono-substituted trialkoxysilanes using sol-gel process is a group of materials that has both chemical durability from the stable three-dimensional network of siloxane bondings and variable properties from the modifying organic functional groups bonded to silicon atoms. Despite their interesting properties, those who handle them face a difficulty in completing the polycondensation of silanol groups. Generally, both using basic catalysts and heat treatment are effective for facilitating the polycondensation in the sol-gel processes of organic-inorganic hybrid silica. In this work, the effect of temperature and catalyst on the polycondensation of sol-gel derived hybrid silica from phenyltriethoxysilane and two vinyltrialkoxysilanes was investigated. In the first work, I experimentally studied the rate process of the polycondensation in the hydrophobic matrix of the partially phenylated hybrid silica from phenyltriethoxysilane (PTES). In this experiment, spherical samples were prepared by pouring the hydrolyzed PTES into a spherical plastic mold with diameter 2.5×10-3 m and cured by heating at 100 °C for 24 hours. Subsequently the as-prepared sample was immersed in a 28% ammonia solution for various durations of time. A shell-like solid structure of the phenyl silica was formed by the gradual polycondensation that started at the outer surface of the as-prepared sample and proceeded inward to the center of the sphere. The thickness of the shell gradually increased with the duration of the immersion in the ammonia aqueous solution. The rate constant of the inward permeation of the catalytic ammonia solution was estimated from the time dependence of the thickness of the shell. It was found that the polycondensation process was entirely rate-determined by the slow inward permeation of ammonia solution from the outer surface of the sample. To elucidate the effects of the heat treatment, sol-gel derived submicron particles from PTES were heated for 192 hours at 260, 280, 300, and 320 °C in air. Subsequently, the obtained submicron particles were dispersed in acetone by ultrasonic agitation to examine their solubility in an amphiphilic solvent. In the cases of the heat treatment at 260 and 280 °C, the ultrasonicated submicron particles partially dissolved, which showed that unreacted silanol groups remained even after the heat treatment for 8 days. The samples which underwent the heat treatment at 300 and 320 °C exhibited no dissolution in acetone, which shows the completion of the polycondensation to form firm three-dimensional network structure by the heat treatment at 300 °C. The results form thermogravimetric (TG) analyses, evaporation behavior of dimethylformamide from the heated samples, scanning electron microscopic (SEM) observations, and Fourier-transform infrared (FT-IR) measurements indicated the completion of the polycondensation of the sample by the heat treatment at 300 °C. In the third work, the completion of polycondensation of sol-gel derived organic-inorganic hybrid silica by heat treatment was studied on powder samples prepared from vinyltrimethoxysilane (VTMS) and vinyltriethoxysilane (VTES). An optimum temperature for completing the polycondensation of the “as-prepared” submicron powdery samples from both starting compounds was determined from TG analysis. The completion or non-completion of the polycondensation of the samples was elucidated by means of a light scattering test. In addition, several instrumental methods such as TG analyses, FT-IR spectroscopy, SEM, and wide-angle X-ray scattering (WAXS) were also employed to confirm the completion of the polycondensation. I determined that the optimum heat treatment condition for the particle from VTMS and VTES is 170 and 180 °C for 24 hours, respectively and this was also confirmed on the basis of the experimental results of the above methods. The morphologies of the heat treated samples were found to be slightly different depending on the starting material. Generally both basic catalysts and heat treatment are very effective in facilitating the polycondensation of the sol-gel derived organic-inorganic hybrid silica from mono-substituted alkoxysilanes. Ammonia solution was found to slowly catalyze the polycondensation of the silanol moiety derived from PTES. The kinetics of the mass transfer of the ammonia solution into hybrid silica matrix was developed based on the measured results of the gradual growth of the completely polycondensed layer. On the other hand, heat treatment was found to drastically enhance the polycondensation of the organic-inorganic hybrid silica powders from PTES, VTMS and VTES. The resultant silica after the heat treatment shows excellent thermal stability. These results will support many engineers and scientists who face the same kind of problem in the development of new products and/or new fabrication processes based on the use of organic?inorganic hybrid silica.
横浜国立大学, 平成24年9月24日, 博士（工学）, 甲第1499号