Abstract：There are many studies on the preparation of superhydrophobic coatings, among which silicon derivative coating is a key point. However, there are a few reports on the formation mechanism of silicon derivatives.In this paper, sodium silicate and ethylene triethoxysilane (VTES) were used as reactants of silicon derivatives. The reaction mechanism of silicon derivatives was studied by near infrared spectroscopy (NIR) and two dimensional correlation analysis (2DCorr). Firstly, the spectral information of samples was collected by MPA Fourier near infrared spectrometer of Bruker Company,Germany. The molecular structure changes of 17 Wt% sodium silicate, 97 Wt% VTES and their blend of 1∶5 molar ratio were analyzed. The results showed that the absorption peaks of Si—O—H and Si—O—Si groups appeared in the range of 5 176~4 250 cm-1 in sodium silicate/VTES blend, which indicated that the hydrolysis and condensation reaction took place after the solutions were mixed. In addition, the free hydroxyl groups at 10 262 cm-1 decreased and shifted to low frequency, and hydroxyl groups associated with hydrogen bond increased at 8 905 cm-1. Secondly, sodium silicate and VTES were mixed and stirred into sol-gel shape according to seven different molar ratios. The spectral information of the samples was also collected by near infrared spectrometer, and the absorption peaks of the related groups in sodium silicate/VTES blend were assigned.The results showed that with the increase of VTES ratio, the number of free hydroxyl groups and alcohols containing hydrogen bond decreased, while the number of combined hydroxyl groups and silicon groups increased. Finally, the spectral data of sodium silicate/VTES blend with different molar ratios were corrected by baseline correction,and the two-dimensional correlation spectra based on molar proportion disturbance were calculated by using the software Matlab 6.5. So, the resolution of the near infrared spectrum was improved and the change sequence among different functional groups was analyzed. The results showed that the change of absorption peak at 10 262 cm-1 was prior than that at 8 905 cm-1, the change of absorption peak at 7 026(6 846) cm-1 was later than that at 5 859 cm-1, the change of absorption peak at 5 264(5 176) cm-1 was later than that at 4 397 cm-1, and the change of absorption peak at 4 667 cm-1 was later than that at 4 397 cm-1. The variation order of absorption peak at different wavenumber corresponded to the variation order of functional group assigned to them, which further revealed the reason for the change of functional groups in near infrared spectra. The sol-gel formed by blending two solutions of sodium silicate and VTES is a silicon-polymer with three-dimensional network structure. The polymer has hydrophobic properties and can be widely used. The results will be helpful to understand the hydrolysis and condensation reaction process and molecular structure changes of sodium silicate /VTES blend, and provide reference for further research and application.
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