Role of Interfacial Charging and Electrostatic Image Forces for Pickering Emulsions

无表面活性剂的油和水的乳状液可以被两种液相具有一定润湿性的胶体颗粒稳定。这些所谓的皮克林乳剂因其良好的稳定性、加工性能和缺乏乳化剂毒性而长期受到赞赏；颗粒作为乳化剂的新兴趣最近被用于刺激反应乳剂和乳剂模板微胶囊中。尽管有这些技术进步，我们对皮克林乳剂的理论认识仍然远远落后：从所用液体和颗粒的性质，甚至是乳化体系的最基本特征，如混合后形成的乳剂类型（o/w或w/o），仍然不可能可靠地预测。本项目旨在建立一个简单的，但预测模型的乳化性质的胶体颗粒在给定的液体混合物。知识价值：从实验和理论上探讨了固体颗粒稳定乳状液的主要因素。具体来说，本项目验证了这样一个假设，即通过考虑单个颗粒与油/水界面的相互作用，可以准确预测三相体系中的“优选乳液类型”，并得出有关可实现乳液稳定性的深远结论。假设考虑了两种通常被忽视的静电对自由能的贡献：油水界面附近带电粒子与其静电图像的相互作用，以及油水界面内带电粒子周围偶极子场中存储的能量。该方法结合了油水颗粒系统中电荷、润湿和远场静电相互作用的实验表征，以及可实现的乳液类型和稳定性的理论建模和模型预测的实验测试。更广泛的影响：该项目的结果将扩大我们对颗粒稳定乳液的基本理解，目前的应用范围从食品配方和护肤霜到石油回收，以及通过智能微胶囊进行溢油修复或药物输送等预期用途。在亚特兰大一所以非裔美国人为主（97%）的学校，通过与课堂教师密切合作的“科学研讨会”，将日常生活中遇到的乳剂科学介绍给学龄前儿童到一年级学生。一个“演示包”，包括最成功的演示的材料和说明，将提供给教师在未来的课程中使用。在大学层面，PI的种族多元化和以女性为主的研究小组以身作则，促进了多样性。该项目的研究成果将直接纳入PI教授的胶体和表面研究生选修课；正在进行的研究定期在PI组织的胶体和软物质研讨会上进行介绍，该研讨会汇集了来自乔治亚理工学院和埃默里大学不同学科的25多个研究小组。

1134398PI: BehrensSurfactant-free emulsions of oil and water can be stabilized by colloidal particles with some wettability by both liquid phases. These so-called Pickering emulsions have long been appreciated for their good stability, processing properties, and lack of emulsifier toxicity; renewed interest in particles as emulsifiers has most recently been sparked by their use in stimulus-responsive emulsions and in emulsion-templated microcapsules. Despite these technological advances, our theoretical understanding of Pickering emulsions lags far behind: it is still impossible to predict reliably, from the properties of the liquids and the particles used, even the most basic features of the emulsified system, such as the type of emulsion (o/w or w/o) formed upon mixing. This project aims at establishing a simple, yet predictive model for the emulsifying properties of colloidal particles in a given liquid mixture.Intellectual Merit: The main factors responsible for emulsion stabilization by solid particles are explored experimentally and theoretically. Specifically this project tests the hypothesis that accurate predictions of the "preferred emulsion type" in a three phase system and far-reaching conclusions about the achievable emulsion stability can be obtained by considering the interaction of individual particles with the oil/water interface ? provided that two commonly neglected electrostatic contributions to the free energy are accounted for: the interaction of charged particles near oil-water interfaces with their electrostatic image, and the energy stored in the dipole field around a charged particle trapped within the oil-water interface. The approach combines the experimental characterization of charging, wetting and far-field electrostatic interactions in oil-water-particle systems with theoretical modeling and experimental tests of model predictions for the achievable emulsion type and stability. Broader Impact: Results of this project will expand our fundamental understanding of particle-stabilized emulsions with current applications ranging from food formulations and skin care creams to oil recovery, and anticipated uses e.g. in oil spill remediation or drug delivery via smart microcapsules. The science of emulsions encountered in everyday life is introduced to preschoolers through first graders in a predominantly (97%) African-American Atlanta school through hands-on "science workshops" in close collaboration with the classroom teachers. A "demo kit" including materials and instructions for the most successful demonstrations will be made available to the teachers for use in future classes. At the collegiate level, the PI's ethnically diverse and predominantly female research group promotes diversity by example. Research results from this project are incorporated directly in a graduate elective course on Colloids & Surfaces taught by the PI; research in progress is presented regularly in a Colloid and Soft Matter seminar organized by the PI, which brings together more than 25 research groups from different disciplines at Georgia Tech and Emory University.