Role of Interfacial Charging and Electrostatic Image Forces for Pickering Emulsions

1134398PI：Behrens油和水的无表面活性剂乳状液可以由胶体颗粒稳定，两种液体都有一定的润湿性。这些所谓的Pickering乳液长期以来一直因其良好的稳定性、加工性能和无乳化剂毒性而受到赞赏；最近，人们对颗粒作为乳化剂的兴趣重新燃起，原因是它们在刺激响应型乳液和乳液模板微胶囊中的使用。尽管有这些技术进步，但我们对Pickering乳液的理论理解仍然远远落后：从液体和所用颗粒的性质，甚至是乳化体系的最基本特征，如混合时形成的乳液类型(O/W或W/O)，仍然无法可靠地预测。该项目旨在建立一个简单的、可预测的胶体颗粒在给定的液体混合物中的乳化性质的模型。具体地说，这个项目测试的假设是，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“首选乳化液类型”，并得出关于可实现的乳化液稳定性的深远结论？假设考虑了两个通常被忽略的静电对自由能的贡献：靠近油-水界面的带电粒子与其静电映象的相互作用，以及在捕获在油-水界面内的带电粒子周围的偶极场中存储的能量。该方法结合了油-水-颗粒体系中电荷、润湿和远场静电相互作用的实验表征，以及对可实现的乳状液类型和稳定性的模型预测的理论建模和实验测试。更广泛的影响：该项目的成果将扩大我们对颗粒稳定乳液的基本了解，目前的应用范围从食品配方和护肤霜到石油回收，以及预期的用途，例如通过智能微胶囊进行漏油补救或药物输送。在亚特兰大一所以非裔美国人为主(97%)的学校里，通过与课堂教师密切合作的实践“科学研讨会”，将日常生活中遇到的乳剂科学通过一年级学生介绍给学龄前儿童。包括最成功演示的材料和说明的“演示工具包”将提供给教师，供将来的课程使用。在大学一级，PI的种族多元化和以女性为主的研究小组以身作则促进多样性。该项目的研究成果直接被纳入了由该研究所教授的一门关于胶体和表面的研究生选修课；正在进行的研究定期在由该研究所组织的胶体和软物质研讨会上发表，该研讨会汇集了来自佐治亚理工学院和埃默里大学不同学科的25个以上的研究小组。

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.