CAREER: Interactions between 2D particles at fluid-fluid interfaces

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Two-dimensional (2D) materials have properties that are unique because they are atomically thin. Properties such as electrical conductivity, mechanical strength, and optical transparency can be significantly enhanced in these materials compared with their “bulk” material counterparts. There is a growing list of 2D materials, the most common examples being graphene, molybdenum disulfide (MoS2), and hexagonal boron-nitride (h-BN). These materials and others are used in a wide range of consumer products including electronic devices and composite materials. One of the challenges of utilizing 2D materials is their fabrication, which is often accomplished by assembling a collection of 2D particles at the microscopic scale to create a larger material with the desired properties. This project will help understand how 2D particles interact with each other when confined to a fluid-fluid interface, a type of confinement that can be used to assemble 2D particles “edge-to-edge”. The project will also develop techniques for fabricating model 2D particles of controlled size and shape, which will advance the experimental work needed to understand these systems. Results from the project will provide fundamental insight about the interactions of 2D particles that scientists and engineers can use to process 2D particles into advanced films, coatings, and composites. In addition, the project team will work with the Summer Multicultural Engineering Training Program (SUMMET) at the Colorado School of Mines to introduce high school seniors to opportunities in undergraduate research. The goal is to increase awareness of undergraduate research as an opportunity available to these traditionally underrepresented students in science and engineering, and ultimately to encourage their participation in science, technology, engineering, and mathematics (STEM) fields.The interaction potential between 2D particles of controlled size, shape, and thickness at air-water interfaces will be measured from direct observation of particle trajectories and particle assemblies. The model 2D particles will be fabricated in-house using photolithography to selectively pattern 2D material films grown via chemical vapor deposition on copper foil. The foil will be placed at the fluid-fluid interface and removed with etchant solution in a sub-phase exchange cell, and the remaining particles will be visualized with interference reflection microscopy. Contact line undulations around particles will be probed with various forms of gel trapping in conjunction with electron microscopy to understand the nature of capillary forces on the particle-particle interactions. The influence of particle-particle interactions on the macroscopic film structure and strength will be investigated with interfacial rheological tools. The overall goal of the project is to understand the nature of the interactions between 2D particles confined to a fluid-fluid interface, and in particular how the low-dimensional morphology of 2D particles plays a role.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.