We investigated a new method for estimating the amount of silanes physisorbed on a silica particle surface treated with silane coupling agents from a weight loss curve measured by thermogravimetric (TG) analysis. The silica particles were treated with 3-glycidoxypropyl trimethoxysilane (GPTMS) or 3-mercaptopropyl trimethoxysilane (MrPTMS) with both dry and wet treatment methods. In the TG curve for silica particles treated with GPTMS, the weight decreased in three steps: 100-1708C (first step), 170-2508C (second step), and 250-4008C (third step). The weight loss in the first step decreased with heating or acetone washing to remove the physisorbed molecules as the posttreatment. The three weight losses were found to be based on physisorbed monomeric silanes (first step), physisorbed polycondensed silanes (second step), and chemisorbed silanes (third step), respectively. The amount of physisorbed silanes on the silane-treated layer could be estimated from the TG curve without solvent washing to remove the physisorbed molecules. The amounts obtained were almost equal to those measured from a comparison of the weight losses for the treated particles before and after acetone washing. A similar tendency was observed for MrPTMS-treated silica. Thus, the amount of physisorbed silanes in silane-coupling-agent-treated silica particles was successfully estimated from the TG measurements. V C 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43256.

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The surface treatment of spherical silica particles using a silane coupling agent with a glycidoxy group was conducted and the effect of the alkoxy group number on the molecular mobility of the silane chain was investigated by 1 H pulse nuclear magnetic resonance (NMR). Silanes with di-alkoxy and tri-alkoxy structures were used, and the silica particles were treated with 2-propanol solution and heated at 120°C for 24 h after solvent evaporation. The surface coverage of the silica surface was in the range from two to three layers. For multilayer coverage, linear chain and network structures were expected to form on the surface by polycondensation reaction using the di-and tri-alkoxy structures, respectively. However, the relaxation times for silane chains with both di-and tri-alkoxy structures measured by pulse NMR were short, which indicates that both silane chains formed rigid network structures. Fourier transform infrared spectroscopic analysis revealed that ring opening of the epoxy group occurred, followed by reaction to form the network structure, even with the di-alkoxy structure. Ring opening of the epoxy group could be reduced by setting the heating temperature at 80°C. There was a significant difference in flexibility between the silane-layers with di-and tri-alkoxy structures after heating at 80°C, as reflected by the relaxation time.

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