Department of Chemical Engineering, Kyung Hee University, Yongin, Gyeonggi-do 17104, South Korea.
Soft Matter. 2017 Sep 20;13(36):6234-6242. doi: 10.1039/c7sm00618g.
The heterogeneous adsorption behaviors of charged colloidal particles to oil-water interfaces were quantitatively and statistically investigated. Using optical laser tweezers, the particles in a sessile water drop formed in an oil phase were laterally translated toward the slope of the oil-water interface and their attachment to the interface was attempted. The adsorption probability was found to logarithmically decrease as the ionic strength decreased and to depend on the holding time during which an optically trapped particle was held at the position closest to the interface. Non-unity of the adsorption probability at particular salt concentrations and the holding time dependence offer an important clue that the particle adsorption to the interface is not deterministic but stochastic. The stochastic adsorption process can be attributed to the surface heterogeneity of colloidal particles that consequently leads to changes in the electrostatic interactions between the particles and the interface. We also demonstrated that the salt dependence on the adsorption properties of the particles, as measured by optical laser tweezers, was consistent with their bulk behaviors with regard to the stability of particle-stabilized emulsions. Furthermore, we revealed the gravity-induced spontaneous adsorption of the particles to the interface under conditions of sufficiently strong ionic strength.
采用光学激光镊子，将油相中的悬浮液滴中的颗粒横向平移到油水界面的斜坡上，并尝试将其附着在界面上。结果发现，吸附概率随离子强度的降低而呈对数下降，并且取决于将光捕获颗粒保持在最接近界面位置的时间。在特定盐浓度和保持时间的依赖性上，吸附概率不为 1 为我们提供了一个重要线索，即颗粒在界面上的吸附不是确定性的，而是随机的。这种随机吸附过程可归因于胶体颗粒的表面不均匀性，这导致颗粒与界面之间的静电相互作用发生变化。我们还证明，通过光学激光镊子测量的颗粒吸附特性的盐依赖性与它们在粒子稳定乳液的稳定性方面的整体行为一致。此外，我们揭示了在足够强的离子强度条件下，颗粒在重力作用下自发地吸附到界面上。
