Effect of Surrounding Solvents on Interfacial Behavior of Gallium-Based Liquid Metal Droplets.

Ji-Hye Kim,Sooyoung Kim,Ye-Jin Park,Ju-Hee So,Hyung-Jun Koo

doi:10.3390/ma15030706

Abstract

Gallium-based liquid metal (GaLM) alloys have been extensively used in applications ranging from electronics to drug delivery systems. To broaden the understanding and applications of GaLMs, this paper discusses the interfacial behavior of eutectic gallium-indium liquid metal (EGaIn) droplets in various solvents. No significant difference in contact angles of EGaIn is observed regardless of the solvent types. However, the presence or absence of a conical tip on EGaIn droplets after dispensing could indirectly support that the interfacial energy of EGaIn is relatively low in non-polar solvents. Furthermore, in the impact experiments, the EGaIn droplet bounces off in the polar solvents of water and dimethyl sulfoxide (DMSO), whereas it spreads and adheres to the substrate in the non-polar solvents of hexane and benzene. Based on the dimensionless We number, it can be stated that the different impact behavior depending on the solvent types is closely related to the interfacial energy of EGaIn in each solvent. Finally, the contact angles and shapes of EGaIn droplets in aqueous buffer solutions with different pH values (4, 7, and 10) are compared. In the pH 10 buffer solution, the EGaIn droplet forms a spherical shape without the conical tip, representing the high surface energy. This is associated with the dissolution of the “interfacial energy-reducing” surface layer on EGaIn, which is supported by the enhanced concentration of gallium ion released from EGaIn in the buffer solution.

Highlights

Gallium-based liquid metal (GaLM) alloys in a liquid state at room temperature have attracted considerable attention because of their fluidity, low viscosity, low toxicity, high electrical/thermal conductivity, and deformability
We investigated the interfacial characteristics of eutectic gallium-indium liquid metal (EGaIn) droplets in different types of polar and non-polar solvents
The difference in contact angles of the EGaIn droplets was insignificant, and the conical tip on top of the EGaIn droplets was formed in solvents with low surface tension

Summary

Introduction

Gallium-based liquid metal (GaLM) alloys in a liquid state at room temperature have attracted considerable attention because of their fluidity, low viscosity, low toxicity, high electrical/thermal conductivity, and deformability. A gallium oxide layer with a thickness of 1–3 nm forms on the GaLM surface, lowering the surface tension to ~0 [1,2,3,4]. Because of the low surface tension, the metals can be patterned into various structures, allowing GaLM to be used in flexible and stretchable electronics, strain or pressure sensors, and biomedical applications [2,5,6,7,8,9,10]. The metals have been handled and used in an inert gas environment for applications that require the oxide-free, metallic surface of GaLMs [11,12]. The gallium oxide skin is reduced in a strong acid or strong base, exposing the pure GaLM to the solvent [15,16]. To date, few studies on this topic have been conducted

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