Osseo-Asare K, Arriagada FJ
Department of Materials Science & Engineering, The Pennsylvania State University, University Park, Pennsylvania, 16802
J Colloid Interface Sci. 1999 Oct 1;218(1):68-76. doi: 10.1006/jcis.1999.6232.
The growth kinetics of silica nanoparticles synthesized by the microemulsion-mediated alkoxide hydrolysis method was investigated with tetraethoxysilane (TEOS) as the silica precursor and polyoxyethylene (5) nonylphenylether (NP-5)/cyclohexane/ammonium hydroxide as the water-in-oil microemulsion system. The time evolution of the mean diameter of the silica particles was determined for different values of the water-to-surfactant molar ratio (R). Particle growth was found to be a slow process, where under typical experimental conditions at room temperature ([TEOS] = 0.024 M, 29.6 wt% NH(3), water-to-TEOS molar ratio (h) = 7.8) the particles achieved their terminal size after several days. During the early stages of the reaction, particle growth followed first-order kinetics, and the observed first-order growth rate constants decreased with increase in R. A reverse micellar pseudophase model (which considered the partition of reactants between the reverse micellar pseudophase and the bulk oil phase) was developed to analyze the growth kinetics under the hypothesis that TEOS hydrolysis was rate controlling. The pseudophase model predicted an inverse relationship between the observed growth rate and R, in agreement with experiment. The roles of steric effects and the bound state of water molecules, in retarding the hydrolysis rate, were highlighted by examining the effect of R on the TEOS hydrolysis rate constant in the reverse micellar pseudophase. Copyright 1999 Academic Press.
以四乙氧基硅烷（TEOS）为硅源前驱体，聚氧乙烯（5）壬基苯基醚（NP - 5）/环己烷/氢氧化铵为油包水微乳液体系，研究了微乳液介导的醇盐水解法合成二氧化硅纳米颗粒的生长动力学。测定了不同水与表面活性剂摩尔比（R）下二氧化硅颗粒平均直径随时间的变化。发现颗粒生长是一个缓慢的过程，在室温下的典型实验条件下（[TEOS] = 0.024 M，29.6 wt% NH₃，水与TEOS摩尔比（h） = 7.8），颗粒在几天后达到其最终尺寸。在反应的早期阶段，颗粒生长遵循一级动力学，并且观察到的一级生长速率常数随R的增加而降低。在TEOS水解为速率控制步骤的假设下，建立了一个反胶束假相模型（该模型考虑了反应物在反胶束假相和本体油相之间的分配）来分析生长动力学。该假相模型预测观察到的生长速率与R呈反比关系，与实验结果一致。通过研究R对反胶束假相中TEOS水解速率常数的影响，突出了空间位阻效应和水分子结合状态在减缓水解速率方面的作用。版权所有1999年学术出版社。
