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

皮克林乳剂是由固体颗粒稳定的油水乳剂。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。与所有乳剂一样，机械搅拌是产生液滴和将颗粒带到液滴表面的必要条件，随着时间的推移，聚并会破坏乳剂。在标准的油水乳状液中，热力学稳定性产生具有非常小且尺寸均匀的液滴的清晰悬浮液。到目前为止，还没有一个等效的、被充分理解的皮克林乳剂的子类，它是热力学稳定和自发的（即不搅拌形成）。自发乳化只在有限的特殊材料中被报道过。基于这种背景，有一个重要的工程原理来设计自发皮克林乳液：均匀的尺寸，更小的液滴，光学上可获得的透明溶液，长保质期，不需要搅拌。我们的首要目标是发展必要的科学理解来设计热力学自发，稳定和可逆的皮克林乳液，工程目标是基于其优势特性实现许多新技术。所获得的设计准则将适用于一系列问题，包括那些具有各向异性或片状粒子的问题。本提案旨在理解和操纵纳米颗粒-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造热力学稳定、自发和可逆的皮克林乳液。为了实现这一目标，需要更好地理解纳米颗粒在流体界面上吸附的热力学，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，实验系统将通过纳米颗粒在流体界面上的吸附特性（分配、可逆性、表面压力、稳定性）进行筛选。基于相互作用势和材料性质的自发、稳定、可逆皮克林乳剂形成的热力学模型将进一步发展。最后，该模型将通过测量与材料相关的粒子-粒子（体相和界面相）和粒子-界面相互作用势来验证。所提出的工作的新颖之处在于系统和迭代的方法，以广泛的吸附表征，严格的建模和粒子间势的独特测量，这将提供：1)可逆平衡条件；2)实现自发乳化的材料参数；3)流体界面上纳米颗粒相互作用的定量测定；4)由于界面上的亚稳构型或缓慢的吸附动力学而无法实现可逆性的条件。对热力学可逆性的关注为依赖外部吸附或乳化调节的技术打开了大门，例如漏油清理、传感和检测或分离。这项工作将通过延长皮克林乳液的保质期和设计更小、光学可及的液滴来加速基于皮克林乳液的技术的发展。在整个项目期间，pi将每周访问一个课后项目，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液的项目。评估结果将通过与教育学院和外部顾问的合作来完成。pi还将为该项目招募几名高中生和本科生。pi将把这个项目的结果纳入两个核心研究生课程。

#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.