Urbina-Villalba German, García-Sucre Máximo
Instituto Venezolano de Investigaciones Científicas (IVIC), Centro de Física, Laboratorio de Fisicoquímica de Coloides, Aptdo. 21827, Caracas 1020-A, Venezuela.
Langmuir. 2005 Jul 19;21(15):6675-87. doi: 10.1021/la050024p.
The kinetic stability of suspensions is usually associated with a decrease in the flux of flocculating particles due to the action of a repulsive potential. However, previous calculations on bitumen drops suggest the possible occurrence of relatively fast aggregation rates in systems with large electrostatic barriers for primary minimum flocculation. This indicates a strong effect of the secondary minimum in the process of aggregation. Here, emulsion stability simulations (ESS) are used to study the aggregation behavior of 11 systems showing different depths of the secondary minimum and three particle sizes. Micron size drops (as those of Bitumen emulsions) usually exhibit deep secondary minima, which rarely occur between nanometer size particles. At high surfactant concentrations, these drops do not coalesce but can still show fast aggregation rates caused by irreversible secondary-minimum flocculation. On the other hand, the extent of coalescence in nanometer-size systems markedly depends on the height of the repulsive barrier. Furthermore, the secondary minimum of these smaller particles is usually shallow, causing reversible aggregation or no aggregation at all. In this article, the consequences of the referred behaviors on the magnitude of the stability ratio are discussed.
悬浮液的动力学稳定性通常与由于排斥势的作用导致絮凝颗粒通量的降低有关。然而，先前对沥青滴的计算表明，在具有较大静电势垒以实现初级最小絮凝的系统中，可能会出现相对较快的聚集速率。这表明在聚集过程中二级最小作用的强烈影响。在此，乳液稳定性模拟（ESS）用于研究11个系统的聚集行为，这些系统呈现出不同深度的二级最小和三种颗粒尺寸。微米级液滴（如沥青乳液的液滴）通常表现出较深的二级最小，这在纳米级颗粒之间很少出现。在高表面活性剂浓度下，这些液滴不会聚结，但仍可能由于不可逆的二级最小絮凝而表现出快速的聚集速率。另一方面，纳米级系统中的聚结程度明显取决于排斥势垒的高度。此外，这些较小颗粒的二级最小通常较浅，导致可逆聚集或根本不聚集。在本文中，将讨论上述行为对稳定性比大小的影响。
