Department of Chemistry, University of Gothenburg, Gothenburg, Sweden.
J Phys Chem B. 2011 Aug 11;115(31):9547-55. doi: 10.1021/jp2032753. Epub 2011 Jul 20.
The effect of ion specificity on the slow aggregation of silica nanoparticles with various initial morphology was investigated with an electrospray-scanning mobility particle sizer (ES-SMPS) and time-resolved synchrotron radiation-small-angle X-ray scattering (SR-SAXS). This combination provides a unique tool to monitor and resolve the early aggregate development in detail. Aggregation was induced by varying the K(2)CO(3) or KCl concentration to obtain a fixed gelation time of ∼40 min, and the results were compared with those obtained in a previous paper (Johnsson et al. J. Phys. Chem. B 2011, 115, 765-775) for NaCl. All dispersions produced gels that contained free primary particles well past the point of gelation (PoG). The initial aggregate formation and obtained gel morphologies were independent of the aggregation initiator. Nevertheless, ion-specific effects were observed for the rate of the stability increase of the 3-dimensional (3D) gel structure. The formation of a stable structure was fastest in the presence of the strongly hydrated counterions, and a clear anion effect was observed. The obtained gel stabilities were interpreted by relating the rate of formation of covalent siloxane bonds to the polarization of the water molecules surrounding structure-maker ions.
采用电喷雾-扫描迁移率颗粒物粒径谱仪（ES-SMPS）和时间分辨同步辐射小角 X 射线散射（SR-SAXS）研究了离子特异性对不同初始形态的硅纳米颗粒缓慢聚集的影响。这种组合提供了一种独特的工具，可以详细监测和解析早期聚集的发展。通过改变 K(2)CO(3)或 KCl 浓度来诱导聚集，以获得固定的胶凝时间约为 40 分钟，并将结果与之前在 NaCl 中获得的结果（Johnsson 等人，J. Phys. Chem. B 2011, 115, 765-775）进行比较。所有分散体产生的凝胶在胶凝点（PoG）之后很长时间内都含有游离的初级颗粒。初始聚集的形成和获得的凝胶形态与聚集引发剂无关。然而，对于三维（3D）凝胶结构稳定性增加的速率，观察到了离子特异性效应。在强水合抗衡离子存在下，稳定结构的形成最快，并且观察到明显的阴离子效应。通过将形成共价硅氧烷键的速率与围绕结构形成离子的水分子的极化相关联，对获得的凝胶稳定性进行了解释。
