Shi Chen, Zhang Ling, Xie Lei, Lu Xi, Liu Qingxia, Mantilla Cesar A, van den Berg Frans G A, Zeng Hongbo
Department of Chemical and Materials Engineering, University of Alberta , Edmonton, AB T6G 2 V4, Canada.
Shell International Exploration and Production Inc., Houston, Texas 77079, United States.
Langmuir. 2016 Mar 15;32(10):2302-10. doi: 10.1021/acs.langmuir.5b04392. Epub 2016 Mar 1.
Emulsions with interface-active components at the oil/water interface have long been of fundamental and practical interest in many fields. In this work, the interaction forces between two oil droplets in water in the absence/presence of asphaltenes were directly measured using droplet probe atomic force microscopy (AFM) and analyzed using a theoretical model based on Reynolds lubrication theory and the augmented Young-Laplace equation by including the effects of disjoining pressure. It was revealed that the interaction forces measured between two pristine oil droplets (i.e., toluene) could be well described by the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, while an additional steric interaction should be included in the presence of asphaltenes in the oil. The surface interaction and the stability of oil droplets in aqueous solution were demonstrated to be significantly influenced by the asphaltenes concentration in oil, salt concentration, pH, and presence of divalent ions (Ca(2+)) in water. Adsorbed asphaltenes at the oil/water interface led to more negative surface potential of the oil/water interface and also induced steric repulsion between oil droplets, inhibiting the drop coalescence and stabilizing the oil-in-water emulsion. Lower pH of aqueous solution could lead to less negative surface potential and weaken the repulsion between oil droplets. Addition of divalent ions (Ca(2+)) was found to disrupt the protecting effects of adsorbed asphaltenes at oil/water interface and induce coalescence of oil droplets. Our results provide a useful methodology for quantifying the interaction forces and investigating the properties of asphaltenes at the oil/water interfaces and provide insights into the stabilization mechanism of oil-in-water emulsions due to asphaltenes in oil production and water treatment.
在油/水界面含有界面活性成分的乳液长期以来在许多领域都具有基础研究和实际应用价值。在这项工作中，使用液滴探针原子力显微镜（AFM）直接测量了在不存在/存在沥青质的情况下水中两个油滴之间的相互作用力，并使用基于雷诺润滑理论和扩展的杨-拉普拉斯方程的理论模型进行分析，该模型考虑了分离压力的影响。结果表明，两个原始油滴（即甲苯）之间测量到的相互作用力可以用经典的德亚金-朗道-韦弗-奥弗比克（DLVO）理论很好地描述，而在油中存在沥青质时应包括额外的空间相互作用。油滴在水溶液中的表面相互作用和稳定性被证明受到油中沥青质浓度、盐浓度、pH值以及水中二价离子（Ca(2+)）的存在的显著影响。吸附在油/水界面的沥青质导致油/水界面的表面电位更负，还诱导了油滴之间的空间排斥，抑制了液滴聚并并稳定了水包油乳液。水溶液较低的pH值会导致表面电位的负性降低并削弱油滴之间的排斥力。发现添加二价离子（Ca(2+)）会破坏吸附在油/水界面的沥青质的保护作用并诱导油滴聚并。我们的结果为量化相互作用力和研究油/水界面处沥青质的性质提供了一种有用的方法，并为油生产和水处理中由于油中的沥青质导致的水包油乳液的稳定机制提供了见解。
