Caratzoulas S, Vlachos D G, Tsapatsis M
Department of Chemical Engineering, University of Delaware, Newark, Delaware 19716, USA.
J Phys Chem B. 2005 May 26;109(20):10429-34. doi: 10.1021/jp0500891.
The stability of silica octamers, Si(8) observed in tetramethylammonium (TMA) solutions by Kinrade et al. is investigated in connection with the TMA concentration by performing equilibrium molecular dynamics simulations of Si(8)-TMA-water mixture at two concentrations. At the experimental concentration at which the silica octamers have been observed spectroscopically, we find that, on the average, six TMA molecules surround the silica octamer, coordinated so that each cation occupies a face of the cubic octamer. We also find that upon TMA adsorption, water molecules associated with the siloxane oxygens leave the silica surface, whereas the hydrogen-bond network of the silanol oxygens with water molecules remains intact. No TMA adsorption is observed at the concentration at which the octamers have not been observed.
Kinrade等人在四甲基铵（TMA）溶液中观察到的硅八聚体Si(8)的稳定性，通过对两种浓度的Si(8)-TMA-水混合物进行平衡分子动力学模拟，研究了其与TMA浓度的关系。在通过光谱观察到硅八聚体的实验浓度下，我们发现平均而言，六个TMA分子围绕着硅八聚体，其配位方式使得每个阳离子占据立方八聚体的一个面。我们还发现，在TMA吸附时，与硅氧烷氧相关的水分子离开硅表面，而硅醇氧与水分子的氢键网络保持完整。在未观察到八聚体的浓度下未观察到TMA吸附。
