Processing and Properties of Functional Liquid Metal Elastomer Composites

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Elastomers (soft polymers) such as silicone are ideal for engineered systems that must mimic the mechanical properties of natural human tissue. By matching the natural properties of the body, these soft and lightweight materials can conform to skin without causing discomfort or injury. Applications include wearable computing and electronics, collaborative robots, medical implants, and other emerging technologies that require mechanical compatibility with clothing, skin, and internal organs. However, these applications also require a range of electrical properties that are not possible with conventional elastomers. While there are several promising techniques to improve the electrical properties of elastomers, these typically involve fillers, additives, or co-polymers that significantly degrade mechanical performance by making the material too stiff. In this project, we will research an alternative approach in which silicone is filled with a suspension of microscopic droplets of liquid metal (LM). Because they are metallic, the droplets can be used to dramatically alter the electrical properties of the composite. Moreover, since they are liquid, they do not cause the silicone to become stiff. LM-embedded elastomer (LMEE) composites represent an exciting new class of materials that will have a potentially transformative impact on wearable computing and soft collaborative robotics, thereby promoting domestic economic growth and quality of life. This project involves several disciplines including manufacturing, chemistry, materials science, and mechanics that will incorporated into both the research tasks and an outreach program on technology-integrated fashion for academically underserved students in the Pittsburgh area.Progress in LMEE engineering depends on new processing techniques and a mechanics-based framework for predicting the influence of materials composition, nano-/micro-scale structure, and liquid-solid interactions on bulk electrical and mechanical properties. The research work will address these aims with an interdisciplinary effort that combines theoretical mechanics modeling, materials processing, and multiscale characterization. This will include efforts to produce LMEE composites with various compositions and process conditions, compare their bulk properties under different testing configurations, and compare these measurements with predictions based on homogenization analysis and statistical mechanics. This work will lead to new scientific insights that will contribute to a fundamental understanding of the unique behavior of the composite under extreme mechanical loading. Together, these tasks will result in a new experimental and theoretical framework that could be applied to enable design other classes of multi-phase soft-matter systems.