Regular Self-Actuation of Liquid Metal Nanodroplets in Radial Texture Gradient Surfaces

Abstract

Liquid metal movement in microfluidic devices generally requires an external stimulus to achieve its motion, which results in many difficulties to precisely manipulate its motion at a nanoscale. Therefore, there is an attempt to control the motion of a liquid metal droplet without the input of an external force. In this paper, we report an approach to achieve the self-actuation of a gallium nanodroplet in radial texture gradients on substrates. The results have proved the validity of this method. It is suggested that there are four stages in the self-motion of the droplet and that the precursor film forming on the second stage plays a pivotal role in the motion. Furthermore, how the impact velocity affects the self-actuation of the nanodroplet on the gradient surface is also studied. We find that the moderate impacting velocity hinders the self-actuation of the gallium nanodroplet. This study is very helpful to regulate the self-actuation on patterned substrates and facilitate their applications in the fields of microfluidics devices, soft robots, and liquid sensors.

Sessile droplet evaporation on the surface of a liquid metal

“…The contact angle of hexane droplets on the surface of liquid gallium in ambient air is the largest, and that in glove box is the smallest. The droplet shape on a substrate surface is related to the surface tension (or surface energy) of the substrate, 25,26 but the measurement of surface tension or surface energy of liquid gallium is beyond the scope of this paper. Wang et al 27 adopted a novel experimental method to measure the surface tension of the oxide film of gallium-based liquid metals.…”

Room‐Temperature Liquid Metals for Flexible Electronic Devices

“…[91] The reactive wetting of LMs is not limited to rigid substrates, as evidenced by the ability of copper sputter-coated and microstructured soft silicane surfaces to exhibit capillary-induced and wetting actuated behavior in HCl vapor. [89] Molecular dynamics suggested wetting induced self-actuation behavior of liquid metals on rough texture gradient surface of carbon and soft stiffness gradient brushes without external energy supply, [92,93] indicating potential applications of molecular actuation of liquid metals. Park et al demonstrated vacuum injection of LM in microchannels and high voltage induced electroadhesion.…”

“…RT-GaLMs are endowed with combination of oxide, fluidic, metallic, and stretchable characters, and can be transformed and actuated to flow, float, shift, wriggle, vibrate, contract, and convection. [54,56,67,92,115,116] That transformability endowed liquid metals and composites to adapt to various shapes of flexible electronic devices through external forces or electric fields, and to be assembled into microdevices to form activatable flexible sys-tems, providing opportunities for advancements in soft robotics and smart devices.…”

Unidirectional self-actuation transport of a liquid metal nanodroplet in a two-plate confinement microchannel

“…Subsequently, some researchers have made great progress in designing and fabricating a wetting gradient surface. In our previous work, 28 radial texture gradient substrates were used to achieve the self-actuation of a gallium nanodroplet. Jiang et al 29 introduced a strategy based on slippery surfaces with immobilized lubricant menisci to directionally transport microdroplets with high efficiency.…”