Leunissen Mirjam E, Zwanikken Jos, van Roij René, Chaikin Paul M, van Blaaderen Alfons
Soft Condensed Matter, Debye Institute, Utrecht University, Princetonplein 5, 3584 CC, Utrecht, The Netherlands.
Phys Chem Chem Phys. 2007 Dec 28;9(48):6405-14. doi: 10.1039/b711300e. Epub 2007 Oct 5.
We present a combined experimental and theoretical investigation of the surprisingly strong electrostatic effects that can occur in mixtures of low- and high-polar liquids (e.g. oil-water emulsions), here in the presence of colloidal particles. For our experiments, we used confocal microscopy imaging, supplemented with electrophoresis and conductivity measurements. Theoretically, we studied our systems by means of a modified Poisson-Boltzmann theory, which takes into account image charge effects and the electrostatic self-energies of the micro-ions in the different dielectric media. Our results show that the unequal partitioning of micro-ions between the two liquid phases is the common driving force behind most of the observed electrostatic effects. The structural signatures of these effects typically develop on a time scale of hours to days and are qualitatively well-described by our theory. We demonstrate how the partitioning process and its associated phenomena can be controlled by shifting the balance of the interlocked ionic dissociation and partitioning equilibria. Moreover, we present strong experimental proof that the two-dimensional colloidal crystals at the oil-water interface are due to long-ranged Coulombic repulsion through the oil phase. The acquired insight in the role of electrostatics in oil-water emulsions is important for understanding the interactions in particle-stabilized ('Pickering') and charge-stabilized emulsions, emulsion production, encapsulation and self-assembly.
我们对低极性和高极性液体混合物（如油水乳液）中可能出现的惊人强静电效应进行了实验与理论相结合的研究，此处是在胶体颗粒存在的情况下。在我们的实验中，我们使用了共聚焦显微镜成像，并辅以电泳和电导率测量。从理论上讲，我们通过修正的泊松 - 玻尔兹曼理论来研究我们的系统，该理论考虑了镜像电荷效应以及不同介电介质中微离子的静电自能。我们的结果表明，微离子在两个液相之间的不等分配是大多数观察到的静电效应背后的共同驱动力。这些效应的结构特征通常在数小时到数天的时间尺度上形成，并且我们的理论对其进行了定性的良好描述。我们展示了如何通过改变相互关联的离子解离和分配平衡的平衡来控制分配过程及其相关现象。此外，我们提供了有力的实验证据，证明油水界面处的二维胶体晶体是由于通过油相的长程库仑排斥作用。对静电在油水乳液中作用的深入了解对于理解颗粒稳定（“皮克林”）和电荷稳定乳液中的相互作用、乳液生产、封装和自组装非常重要。
