ABSTRACT

Multiphase systems such as emulsions or foams are important for many industrial processes and products. Dissolved or suspended materials can meet at interfaces between phases, react, accumulate, and undergo phase transfer. Bijels are a relatively new class of materials in which the two distinct phases are both continuously connected through interpenetrating networks (rather than having islands of one phase within another phase). In bijels, the two phases are stabilized by forming a densely packed layer of particles at the interface between phases. The principle investigator has recently discovered a new process for making bijels. This process expands dramatically the range of liquid pairs that can be used and allows the bijel structure to be tailored. The present work is a detailed study of how to control and tune bijel structure and properties. In addition, fluid flow and mass transfer within these materials will be measured to assess their potential use in applications. A third study will involve a demonstration of bijel use in a two-phase chemical reaction with continuous flow. This project will uncover the principles that determine the structure of bijels and will lead to new and well-designed multiphase materials for industrial applications. Potential applications range from enhanced product purification in chemical plants to industrial synthesis of high-value added chemicals in bijels. A broad range of educational and outreach activities aimed at middle school, high school, undergraduate and graduate students are also integrated into the research plans.

The objective of this work is to determine whether bicontinuous interfacially jammed emulsion gels (bijels) formed by Solvent Transfer Induced Phase Separation (STRIPS) can be employed for continuously operated and efficient phase transfer processes. Initial work will focus on control over bijel structure and properties. Bijels will be formed with a selection of functional inorganic colloidal particles with surface modifications that will be developed and characterized. The hydrophilic/hydrophobic nature and the repulsive/attractive character of surface functional groups are expected to govern bijel architecture and stability; this will be tested through surface modification of nanoparticles, characterization of surfaces, bijel formation, and characterization of bijel structure and mechanical properties. A second thrust of the work will determine how the mechanical properties of bijels can be tailored to withstand the pressures needed to drive flow. A scheme for reinforcing the interfacially jammed layer of nanoparticles has been developed and a tool has been constructed to characterize pressure-driven flow in bijels and assess their structural integrity under flow conditions. The third aspect of the study involves phase transfer processes under continuous flow in bijels. Continuous extraction in bijels will be demonstrated, followed by study of phase transfer catalysis of a model reaction in a bijel. Educational and outreach activities include the development of a "droplet engineering" course for high school students, a course on colloidal and interfacial engineering for undergraduates, a course on soft matter nanotechnology for graduate students, and expansion of instructional videos on the principle investigator's YouTube channel.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

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