Collaborative Research: Scalable Manufacturing Enabled by Highly Tunable Multiphase Liquid Metal Pastes with Solid and Fluid Capsule Additives

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Liquid metals such as gallium and its alloys have a variety of prospective applications such as in electronic devices, catalysis, energy harvesting and biomedical use but face challenges with manufacturing, tunability and cost that limit them from widespread use. This research project seeks to investigate how incorporating small-scale solid and/or fluid fillers into the liquid metal, i.e. liquid-metal pastes, have the potential to extend the range of physical and chemical properties and increase their economic appeal for additive manufacturing and other technologies. To overcome the challenges associated with the high cohesive energy density of liquid metals, the team proposes to use naturally formed nanometer-thin gallium-oxide shells as a wetting agent (or surfactant) for encapsulating foreign materials of different phases. The resultant liquid-metal pastes represent a novel class of materials with unexplored properties that can advance wearable electronics, soft robotics, and thermal management of electronics. The visual and hands-on nature of the proposed research will enable multiplatform community outreach including engaging K-12 tour groups with a hands-on activity using a video-game controller to operate a three-dimensional printer in making liquid-metal parts.This research aims to realize a generalized way to encase gases, liquids, and solids inside liquid metals and to understand the role of the encasing native oxide in doing so, which creates a unique “surfactant” that forms in situ. These multiphase materials will be formed by mixing (or bubbling fluids) under controlled conditions and subsequently characterized thoroughly to establish process-structure-property relationships. The investigation will elucidate the mechanism by which this oxide “surfactant” works to create foams and pastes with trapped air pockets and liquids or solid objects, respectively. The oxide “enveloping” ability will enable a new class of conductive multiphase pastes with highly tunable density, rheology, as well as electrical and thermal conductivities. With the new fundamental insight, this project will also aim to create liquid-metal based materials that can be effectively three-dimensionally printed onto substrates with almost any composition and shape for two specific studies. The first one is to achieve a foam that is up to 10 times more cost-effective and lighter than pure liquid metals and yet fits for stretchable electronic devices. The second study is to create a paste that secretes small amounts of secondary liquid when applied and thereby improves thermo-mechanical contacts of next-generation thermal interface materials.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.