PREPARATION OF ORGANIC-INORGANIC COMPOSITE MATERIALS USING SOL-GEL TECHNOLOGY

Abstract

This article reviews the principles of hydrolytic polycondensation of tetramethoxysilane (TMOS) in alkaline media. Depending on the concentration of tetramethoxysilane, both nanoscale mono-disperse SiO2 particles and monolithic samples of xerogels were synthesized. Pyridine derivatives, representatives of several chemically and thermally stable aromatics, which perform the function of catalysts, were selected for the work. During the sol-gel process of hydrolysis of tetramethox-ysilane and the polycondensation of the compounds formed with the presence of 4-(dimethylamino)-pyridine as a catalyst, a linear increase in the pKa of the conjugate acid to 9.70 was observed. Since the particles formed in an alkaline environment are negatively charged and repel each other, their growth occurs by the condensation mechanism due to the dissolution of smaller particles. Heating the sol-gel system for 30 minutes does not increase the particle size, but brings the gela-tion point closer. Thus, a small amount of catalyst leads to the formation of a group of particles with a small diameter and a tendency to polycondensate, but a larger amount of catalyst concen-trationcausing the formation of very large particles. The physico-chemical properties of the synthe-sized particles were determined. The dimensions of the processed samples were recorded using a scanning electron microscope (SEM). Keywords: Sol-gel, hydrolysis, polycondensation, tetramethoxysilane, xerogel, pKa, catalyst, SEM.