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.

Herein, we present a humidity sensing microfiber based on an agarose polymer as a hydrophilic matrix and carbon nanotubes (CNT) as conducting fillers. The humiditydependent resistance is the key property of the composite microfiber as a humidity sensor. The composite microfiber composed of the agarose matrix swells or contracts depending on environmental humidity, leading to changes in junction density between the carbon nanotube conducting fillers inside the fiber. Moreover, adsorption of water molecules on the CNT filler could further increase the resistance of the microfiber sensor. The real-time resistance monitoring of the microfiber shows reliable and reversible response to the repetitive changes in relative humidity with reasonable response rate. The tensile strength test confirms the mechanical robustness of the composite microfiber. The fabrication process is facile and presumably scalable. Such a practical fiber sensor could be readily used as a humidity-sensing component in smart textile and wearable devices. POLYM. COMPOS., 40:3582-3587, 2019.

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