UNS: Design of stable spontaneous Pickering emulsions by modulating nanoparticles interactions

#1510671 Frechette，JoellePickering乳液是由固体颗粒稳定的油水乳液。它们在食品科学、消费品、浮选、石油回收和催化方面都很重要。与所有乳状液一样，机械搅拌是产生液滴并将颗粒带到液滴表面所必需的，随着时间的推移，聚合作用会破坏乳状液。在标准的油水乳状液中，热力学稳定性可产生液滴非常小且大小均匀的透明悬浮液。到目前为止，还没有一种同等的、广为人知的Pickering乳状液是热力学上稳定的和自发的(即形成而不搅拌)。自发乳化只在有限的几种独特材料中被报道过。基于这一背景，设计自发的Pickering乳液具有重要的工程原理：尺寸均匀、液滴较小、可光学访问的透明溶液、保质期长且无需搅拌。我们的总体目标是发展对设计热力学自发、稳定和可逆的Pickering乳液所需的科学理解，工程目标是使许多基于其优势特性的新技术成为可能。所获得的设计指南将适用于一系列问题，包括具有各向异性或片状粒子的问题。这项建议旨在了解和操纵纳米颗粒-纳米颗粒和纳米颗粒-界面的相互作用，以开发一种独特的方法来创建热力学稳定的、自发的和可逆的Pickering乳液。为了实现这一目标，需要更好地了解纳米颗粒在流体界面上的吸附热力学，并且需要阐明颗粒-颗粒相互作用以及颗粒与界面之间的作用。作为第一步，将通过表征纳米颗粒在流体界面上的吸附(分配、可逆性、表面压力、稳定性)来筛选实验体系。接下来将建立一个基于相互作用势和材料性质的自发、稳定、可逆Pickering乳液形成的热力学模型。最后，通过测量与材料相关的颗粒-颗粒(体相和界面相)和颗粒-界面相互作用势对模型进行了验证。这项工作的创新之处在于系统和迭代的方法，以实现广泛的吸附表征、严格的建模和独特的颗粒间势测量，这些将匹配提供：1)可逆平衡的条件，2)实现自发乳化的材料参数，3)流体界面纳米颗粒相互作用的定量确定，以及4)由于界面亚稳构型或缓慢的吸附动力学而无法实现可逆的条件。热力学可逆性的关注为依赖外部调节的吸附或乳化技术打开了大门，如清理溢油、传感和检测或分离。这项工作将通过延长保质期和设计更小且可光学访问的液滴来加速基于Pickering乳液的技术的开发。在整个项目期间，PI将每周访问一个课外项目，并在学生参与STEM设计项目时为他们提供指导，并将介绍一个关于乳剂的项目。结果的评估将通过与教育学院和外部顾问的合作进行。PIS还将为这个项目招收几名高中生和本科生。督导计划将把这项计划的成果纳入两项核心研究生课程。

#1510671Frechette,JoellePickering emulsions are oil-water emulsions stabilized by solid particles. They are important in food science, consumer products, flotation, oil recovery, and catalysis. As with all emulsions, mechanical agitation is necessary to create droplets and to bring the particles to the drop surfaces, and over time coalescence breaks the emulsions. In standard oil-water emulsions, thermodynamic stability yields clear suspensions with droplets that are very small and uniformly sized. To date there is not an equivalent, well-understood, sub-class of Pickering emulsions that are thermodynamically stable and spontaneous (i.e., form without agitation). Spontaneous emulsification has only been reported for a limited set of unique materials. Based on this background, there is an important engineering rationale to design spontaneous Pickering emulsions: uniform sizes, smaller droplets, optically accessible clear solutions, long shelf-life, and no need for agitation. Our overarching objective is to develop the scientific understanding necessary to design thermodynamically spontaneous, stable, and reversible Pickering emulsions, with the engineering goal to enable numerous new technologies based on the their advantageous properties. The design guidelines obtained will apply to a range of problems, including those with anisotropic or patchy particles. This proposal aims to understand and manipulate nanoparticle-nanoparticle and nanoparticle-interface interactions to develop a unique means to create thermodynamically stable, spontaneous, and reversible Pickering emulsions. To achieve this goal, a better understanding of the thermodynamics of nanoparticle adsorption at fluid interfaces is needed, and the role played by particle-particle interactions as well as between a particle and the interface needs to be elucidated. As a first step, the experimental systems will be screened via the characterization of the adsorption of nanoparticles to the fluid interface (partitioning, reversibility, surface pressure, stability). A thermodynamic model for the formation of spontaneous, stable, reversible Pickering emulsions based on interaction potentials and material properties will be developed next. Finally, the model will be validated by measuring material dependent particle-particle (in bulk and interfacial phases) and particle-interface interaction potentials. The novelty of the proposed work lies in the systematic and iterative approach toward extensive adsorption characterization, rigorous modeling, and unique measurements of interparticle potentials, which will dovetail to provide: 1) conditions for reversible equilibrium, 2) material parameters to achieve spontaneous emulsification, 3) quantitative determination of nanoparticle interactions at fluid interfaces, and 4) conditions where reversibility cannot be achieved, either due to metastable configurations at the interface or slow adsorption kinetics.THe focus on thermodynamic reversibility opens the door to technologies relying external modulation of adsorption or emulsification, such as cleanup of oil spills, sensing and detection, or separation. The work will accelerate the development of technologies based on Pickering emulsions by increasing shelf-life and by the design of smaller and optically accessible droplets. Throughout the duration of the project the PIs will visit an afterschool program weekly and provide mentoring to students as they engage in STEM design projects, and will introduce a project on emulsions. Assessment of outcomes will be done via collaboration with the School of Education and outside consultants. The PIs will also recruit several high school students and undergraduate students for this project. The PIs will incorporate the results of this project into two core graduate courses.