ビニルトリエトキシシランによる二酸化チタンの疎水化

抄録

The hydrolysis and condensation of Vinyltriethoxysilane (VTES) in a preliminary treatment solution, consisting of VTES, ethanol, and water acidified with acetic acid was investigated using gel permeation chromatography (GPC). This was done to determine the variation in water content over time to obtain information about the useful treatment of TiO₂ with a silane coupling agent.
The main results obtained are as follows: 1) VTES sedimented onto TiO₂ treated with VTES does not necessarily demonstrate the hydrophobicity of TiO₂. 2) An increase in the pH of the aqueous solution results in a delay in the condensation reaction to dimer or higher order polymers. In contrast, an increase in the water content leads to a remarkable acceleration of the hydrolysis and condensation polymerization of VTES. 3) For effective preliminary treatment of TiO₂, conditions must be selected, under which the monomer disappears rapidly and polymers of polymerization numbering 2-4 are stable for a long period. 4) The induction period detected from the rate curve of the variation in water content corresponds to the hydrolysis reaction of the ethoxy group and water content variation cannot be determined by the Karl Fischer method. Thus, the average degree of polymerization can be calculated from the equation for the condensation reaction. 5) The M value that indicates the degree of hydrophobicity increases with a slight increase in the degree of polymerization, reaching M=30% at an average degree of polymerization of 1.1 (corresponding to a 0.5mass% decrease in water content). However, it is necessary to select a suitable preliminary treatment solution and stable conditions for an average degree of polymerization of 2-4 must be selected in order to reach M=35%.