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首页> 外文期刊>The journal of physical chemistry, C. Nanomaterials and interfaces >Kinetics of Oxalic Acid Catalyzed and Ultrasound-Assisted Hydrolysis of 3-Glycidoxypropyltrimethoxysilane and Structural Characteristics of the Resulting Aged Sonogels
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Kinetics of Oxalic Acid Catalyzed and Ultrasound-Assisted Hydrolysis of 3-Glycidoxypropyltrimethoxysilane and Structural Characteristics of the Resulting Aged Sonogels

机译：草酸催化和超声辅助水解3-缩水甘油氧基丙基三甲氧基硅烷的动力学及生成的老化Sonogels的结构特征

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摘要

A kinetic study of the oxalic acid catalyzed and ultrasound-assisted hydrolysis of 3-glycidoxypropyltrimethoxysilane (GPTMS) was carried out using an ultrasound-adapted calorimetric method. During a relatively short time period (t(p)), the hydrolysis follows a heterogeneous pathway because of the initial immiscibility gap between GPTMS and water. Methanol produced in the early hydrolysis enhances the dissolution between GPTMS and water so that the hydrolysis crosses to a homogeneous pathway. A rate equation with a rate constant (k) of the order 3/4 with respect to GPTMS and first order with respect to water seems to describe well the experimental data in the homogeneous step of the reaction. k increased with increasing oxalic acid concentration up to a plateau value (similar to 3.2 x 10(-3) M-3/4 s(-1)) at an oxalic acid concentration of about 0.083 M in the range studied (from 0.014 to 0.14 M). The rate constants k and 1/t(p) (proportional to k in the heterogeneous step) were found to follow approximately an Arrhenius equation with the hydrolysis temperature in the studied range (from 5 to 50 degrees C). The average activation energy for GPTMS sono-hydrolysis was found to be Delta E = (21.5 +/- 1.9) kJ/mol. The structure of aged sonogels exhibited characteristics of a two-phase system (pore and hybrid solid phase) separated by a surface-fractal interface. The hybrid solid phase of the sonogels was constituted by polymeric linear chains, density fluctuation heterogeneities, and several intermolecular-interfering cagelike structures. The phase separation increased with increasing the hydrolysis temperature, apparently at the expense of the polymeric linear chains and the density fluctuation heterogeneities, and led to intensification of the intermolecular-interfering cagelike structures within the hybrid solid phase.
机译：使用超声量热法对草酸催化和超声辅助水解3-环氧丙氧基丙基三甲氧基硅烷（GPTMS）进行了动力学研究。在相对较短的时间段内（t（p）），由于GPTMS与水之间的初始不混溶性缺口，水解遵循非均质途径。早期水解过程中产生的甲醇增强了GPTMS与水之间的溶解度，因此水解过程会穿越均质途径。相对于GPTMS，速率常数（k）为3/4阶，相对于水，为一阶的速率方程似乎很好地描述了反应均相步骤中的实验数据。在研究范围内（0.014至0.01） 0.14 M）。发现速率常数k和1 / t（p）（在非均相步骤中与k成正比）在水解温度处于研究范围内（5至50摄氏度）时近似遵循Arrhenius方程。发现GPTMS声波水解的平均活化能为ΔE＝（21.5 +/- 1.9）kJ / mol。老化的声波凝胶的结构表现出由表面分形界面隔开的两相系统（孔和杂化固相）的特征。声波凝胶的杂化固相由聚合物线性链，密度波动异质性和几种分子间干扰的笼状结构组成。相分离随着水解温度的升高而增加，显然以聚合物线性链和密度波动不均一性为代价，并导致杂化固相内分子间干扰笼状结构的增强。

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