Monitoring tetraethoxysilane hydrolysis/condensation in solutions with low alcoholic content by infrared spectroscopy

ABSTRACT The objective of this work was to monitor the hydrolysis/condensation of tetraethoxysilane (TEOS) as a function of the silane dilution time, through infrared (IR) spectroscopy. Initially two concentrations of silane (1 and 10% by volume) were evaluated. However, it was found that at 1% of TEOS concentrations it was not possible to identify the chemical bonds of interest for the hydrolysis monitoring adequately in regions characteristic of the infrared spectrum. Once the appropriate concentration was defined, the hydrolysis/condensation monitoring was carried out using the infrared spectra obtained in solutions hydrolyzed at room temperature and extracted every 10 minutes. It was found that the hydrolysis reactions of the alkoxy groups accelerated in 40 minutes from the TEOS dilution. In parallel, the condensation of the silanols also accelerated, due to the increase in their concentration in the solution. After 70 minutes, the hydrolysis/condensation showed a deceleration through siloxane formation and due to the complete hydrolysis of the TEOS alkoxy groups. The hydrolysis of TEOS in solutions with low alcohol content (around 50% by volume) did not show any damage to the monitoring of the reactions of interest of the system, presenting reaction kinetics similar to those reported in the literature, showing up as an alternative to systems with excessive consumption of organic solvents.

摘要 本研究旨在通过红外（Infrared, IR）光谱法，监测正硅酸乙酯（tetraethoxysilane, TEOS）的水解/缩合反应随硅烷稀释时间的变化规律。实验初始阶段分别评估了两种体积分数的硅烷体系（1%和10%），但发现当TEOS体积分数为1%时，无法在红外光谱特征区域内有效识别水解监测所需关注的化学键。确定适宜浓度后，本研究通过采集室温下水解体系每10分钟一次的红外光谱，开展水解/缩合反应监测。结果表明，烷氧基的水解反应在TEOS稀释后的40分钟内速率显著提升；与此同时，溶液中硅醇浓度随反应推进逐渐升高，其缩合反应速率也随之加快。反应进行至70分钟后，由于TEOS的烷氧基已完全水解，体系通过生成硅氧烷链使水解/缩合反应速率逐渐放缓。在乙醇体积分数约为50%的低醇体系中，TEOS水解反应未对目标监测反应造成干扰，其反应动力学与文献报道结果一致，可作为有机溶剂消耗量过高体系的替代方案。