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

Johns Hopkins University, Baltimore MD

Investigators

Abstract

#1510671 Frechette,Joelle Pickering 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.