A Surface Modification Approach to Overcome Wetting Behavior of Gallium-Based Liquid Metal Droplets

Abstract

Gallium based eutectic alloys are one of the promising substitutes for mercury. These alloys are nontoxic and environment friendly and have similar or equivalent properties as that of mercury. These alloys exhibit good electrical and thermal properties. However, these alloys form oxides when in contact with oxygen atoms. Due to this, the material surface tension changes, which renders them unsuitable for those applications where the mobility of the fluid is a valuable factor, such as in thermometers and blood pressure monitoring devices. There are few methods reported to remove the oxide layer from the surface of the gallium-based alloys, like acid and base treatment prior to use, but all these methods are not durable and long-lasting. Here in this work, we report gallium oxide coating as a simple approach to convert mercury manometer glass tube, which has glass as a substrate to a nonwetting surface against surface-oxidized gallium-based liquid metal alloys. These alloys form an oxidized layer in ambient air (<inline-formula><tex-math notation="LaTeX">$O_{2}$</tex-math></inline-formula> <inline-formula><tex-math notation="LaTeX">$&gt;$</tex-math></inline-formula>1 ppm) and show stickiness to almost all surfaces that impact the residue-free movement of the liquid metal droplets. Herein, the physical vapor deposition technique was used for gallium oxide coating on substrates such as silicon wafer and glass slide. Moreover, various characterizations were carried out to support our outcomes. This method does not require any micro/nano machining or specific nanoscale surface topology. The contact angle was measured with or without coated gallium oxide film on the glass substrate, and the static contact angle (c.a.) 137.69<inline-formula><tex-math notation="LaTeX">$^\circ$</tex-math></inline-formula> and with bared glass 94.30<inline-formula><tex-math notation="LaTeX">$^\circ$</tex-math></inline-formula>.