Green D L, Lin J S, Lam Yui-Fai, Hu M Z-C, Schaefer Dale W, Harris M T
Chemical Engineering Department and Institute of Physical Science and Technology, University of Maryland, College Park, MD 20742, USA.
J Colloid Interface Sci. 2003 Oct 15;266(2):346-58. doi: 10.1016/s0021-9797(03)00610-6.
29Si NMR, small-angle X-ray scattering (SAXS), and dynamic light scattering (DLS) are used to monitor the synthesis of silica nanoparticles from the base-catalyzed hydrolysis of TEOS in methanol and ethanol. The reactions are conducted at a [TEOS] =0.5 M, low concentrations of ammonia ([NH(3)] =0.01-0.1 M), and [H(2)O] =1.1-4.4 M to resolve the initial size of the first nuclei and to follow their structural evolution. It is found that after an induction period where there is a buildup of singly hydrolyzed monomer, the first nuclei are fractal and open in structure. Interestingly, the nuclei are twice as large in ethanol (R(g) approximately 8 nm) as those in methanol (R(g) approximately 4 nm). The data suggest that the difference in primary particle size is possibly caused by a higher supersaturation ratio of the singly hydrolyzed monomer in methanol than in ethanol if it is assumed that the surface energy of the first nuclei is the same in methanol and ethanol. The particle number concentration and the volume fraction of the silica particles are calculated independently from the SAXS, DLS, and 29Si NMR results. Finally, the rate of nucleation is obtained from the particle number concentrations.
利用29Si核磁共振、小角X射线散射（SAXS）和动态光散射（DLS）来监测在甲醇和乙醇中通过TEOS的碱催化水解合成二氧化硅纳米颗粒的过程。反应在[TEOS]=0.5 M、低浓度氨（[NH₃]=0.01 - 0.1 M）和[H₂O]=1.1 - 4.4 M的条件下进行，以确定第一个核的初始尺寸并跟踪其结构演变。结果发现，在单水解单体积累的诱导期之后，第一个核是分形的且结构开放。有趣的是，乙醇中的核（R(g)约为8 nm）是甲醇中的核（R(g)约为4 nm）的两倍大。数据表明，如果假设第一个核在甲醇和乙醇中的表面能相同，那么初级颗粒尺寸的差异可能是由甲醇中单水解单体的过饱和度比乙醇中的更高所致。根据SAXS、DLS和29Si NMR结果独立计算二氧化硅颗粒的颗粒数浓度和体积分数。最后，从颗粒数浓度获得成核速率。
