Session: 01-01: Liquid Metals

Paper Number: 112282

112282 - Adding Solid and Fluids to Liquid Metals: How to Make Multifunctional Liquid Metal Pastes, Foams, and Emulsions 

Gallium and its eutectic alloys have metallic properties (e.g. high electrical and thermal conductivity) while remaining in liquid state near room temperature. Accordingly, these liquid metals (LMs) are used to make soft and stretchable components and devices for electronics, biomedical, sensor, energy storage, and foremost for thermal management applications. However, the use of the LM is cumbersome because of its rapid oxidation, low viscosity, high surface tension, and reactivity with other metals. These issues can be resolved by adding a variety of solid additives into the LM, which also results in pastes with enhanced properties. Most recently, several routes have also been developed to incorporate secondary fluids into LMs including airto create foams [1,2] and silicone oils to create emulsions[3,4]. Both the foams and emulsions are substantially lighter and easier to apply to surfaces than original LM. In addition, the oil-in-liquid metal emulsions can prevent one of the major drawbacks of gallium and its alloys. Specifically, the emulsion form about 500 nm exterior film that prevents gallium-induced embrittlement of a contacting aluminum surfaces [3,4].  Despite these interesting properties, our understanding of how these LM-based materials form and can be improved on is just beginning to emerge.

In this presentation I will describe the highly intertwined microscale formation mechanisms of LM pastes, foams, and emulsions. First, I will discuss systematic experiments on the internalization of a several sizes and volume fractions of silica microparticles into LM, which demonstrate that some air bubble entrapment always occurs along with particles. Similarly, the experiments demonstrate that addition of solid micro-particles is required for the onset of LM foaming. In other words, there are no pure LM pastes or LM foams but multiphase LM composites with varying volume fractions of solid and air components. The particles size, volume fraction, and mixing method can be used to either promote or inhibit air entrapment leading to more paste-like or foam-like composites. Second, I will discuss formation of the oil-in-LM emulsions. When mixed with any other liquid, pure LM breaks-up into microdroplets. We discovered that this can be prevented when silicone oil is mixed with LM foam. I will discuss how the silicone oil droplets are internalized in the LM foam, and how prior addition of even a small volume fraction of silica particles into LM removes the need for foaming of the liquid before oil addition.

We acknowledge funding from National Science Foundation grant 2034015.

[1]       Wang, X., Fan, L., Zhang, J., Sun, X., Chang, H., Yuan, B., Guo, R., Duan, M., and Liu, J., 2019, “Printed Conformable Liquid Metal E‐Skin‐Enabled Spatiotemporally Controlled Bioelectromagnetics for Wireless Multisite Tumor Therapy,” Adv Funct Mater, p. 1907063.

[2]       Kong, W., Shah, N. U. H., Neumann, T. v, Vong, M. H., Kotagama, P., Dickey, M. D., Wang, R. Y., and Rykaczewski, K., 2020, “Oxide-Mediated Mechanisms of Gallium Foam Generation and Stabilization during Shear Mixing in Air,” Soft Matter, 16, pp. 5801–5805.

[3]       Shah, N. U. H., Kong, W., Casey, N., Kanetkar, S., Wang, R. Y.-S., and Rykaczewski, K., 2021, “Gallium Oxide-Stabilized Oil in Liquid Metal Emulsions,” Soft Matter, 17, pp. 8269–8275.

[4]       Shah, N. U. H., Kanetkar, S., Uppal, A., Dickey, M. D., Wang, R. Y., and Rykaczewski, K., 2022, “Mechanism of Oil-in-Liquid Metal Emulsion Formation,” Langmuir, 38(43), pp. 13279–13287.

Presenting Author: Konrad Rykaczewski Arizona State University

Presenting Author Biography: Konrad Rykaczewski is an associate professor at School for Engineering of Matter, Transport and Energy at ASU. He received his BS (2005), MS (2007) and PhD (2009) in mechanical engineering from the Georgia Institute of Technology under supervision of Prof. Andrei Fedorov. Prior to his appointment at ASU, he was a research scientist at MIT and NRC postdoctoral fellow at NIST.