Kallay Nikola, Zalac Suzana
Department of Chemistry, Faculty of Science, University of Zagreb, Marulićev trg 19, P.O. Box 163, Zagreb, HR 10000, Croatia.
J Colloid Interface Sci. 2002 Sep 1;253(1):70-6. doi: 10.1006/jcis.2002.8476.
In the course of aggregation of very small colloid particles (nanoparticles) the overlap of the diffuse layers is practically complete, so that one cannot apply the common DLVO theory. Since nanopoarticles are small compared to the extent of the diffuse layer, the process is considered in the same way as for two interacting ions. Therefore, the Brønsted concept based on the Transition State Theory was applied. The charge of interacting nanoparticles was calculated by means of the Surface Complexation Model and decrease of effective charge of particles was also taken into account. Numerical simulations were performed using the parameters for hematite and rutile colloid systems. The effect of pH and electrolyte concentration on the stability coefficient of nanosystems was found to be more pronounced but similar to that for regular colloidal systems. The effect markedly depends on the nature of the solid which is characterized by equilibrium constants of surface reactions responsible for surface charge, i.e., by the point of zero charge, while the specificity of counterions is described by their association affinity, i.e., by surface association equilibrium constants. The most pronounced is the particle size effect. It was shown that extremely small particles cannot be stabilized by an electrostatic repulsion barrier. Additionally, at the same mass concentration, nanoparticles aggregate more rapidly than ordinary colloidal particles due to thier higher number concentration.
在非常小的胶体颗粒（纳米颗粒）聚集过程中，扩散层几乎完全重叠，因此不能应用常见的DLVO理论。由于纳米颗粒与扩散层的范围相比很小，该过程的考虑方式与两个相互作用的离子相同。因此，应用了基于过渡态理论的布朗斯特概念。通过表面络合模型计算相互作用的纳米颗粒的电荷，并考虑颗粒有效电荷的降低。使用赤铁矿和金红石胶体系统的参数进行了数值模拟。发现pH值和电解质浓度对纳米系统稳定性系数的影响更为显著，但与常规胶体系统类似。该影响明显取决于固体的性质，其由负责表面电荷的表面反应的平衡常数表征，即由零电荷点表征，而抗衡离子的特异性由它们的缔合亲和力表征，即由表面缔合平衡常数表征。最显著的是粒径效应。结果表明，极小的颗粒不能通过静电排斥屏障来稳定。此外，在相同质量浓度下，由于纳米颗粒的数量浓度较高，它们比普通胶体颗粒聚集得更快。
