In recent year, liquid metals (LM), which have low melting points and remain liquid state under room temperature, have been arousing soaring attention in related research area. Due to some outstanding properties of LM including high thermal and electrical conductivity and nontoxicity, it has been utilized in wide range of applications such as microfluidics, thermal management, soft electronics and so on. Although the research of LM has been increasing both in number and quality, the wetting mechanism of LM on different substrates is still not investigated thoroughly. Under ambient environment, an oxide layer will rapidly form on LM and it adheres to most surfaces, thus affecting the wetting of LM significantly. The adhesion of the oxide layer of LM is a double-edge sword, and there are both works trying to enhance or eliminate it for different substrates and different environments. Thus, the aim of my thesis is to study the wetting status of LM under the effect of water and utilize it for practical applications.

First, we reveal the effect of water film on the impact of LM droplet and achieve tunable surface tension of LM droplet during impact. It is demonstrated that a gallium based liquid metal alloy (EGaIn) could retain two different surface tensions at the same time. By utilizing the naturally-grow oxide layer of EGaIn and adjusting its composition, the surface tension of the liquid metal alloy could be controlled, which is visualized by impact experiment of EGaIn droplets impacting on substrates with water films of different thicknesses. The mechanism of how the water film affects the surface tension of LM is unveiled and afterward applied in the application of selective printing of LM and enhancing mobility for our designed robot. With this unique adjustability of surface tension, EGaIn is anticipated to be widely applied to both research and practical areas.

Meanwhile, we are also seeking ways to enhance the wetting of LM under wet environment, or even under water. The fascinating properties of the oxide layer of LM attract researchers from various area such as fluidics and electronics. More specifically, the strong adhesion of the oxide layer enables LM to be widely applied in printing and electronic fabrication. However, once exposed to water, the adhesion of LM oxide layer will be greatly reduced, hindering the application of LM under humid environment or underwater. Here, we propose an adhesive coating, p(DMA-MEA), for enhanced adhesion of LM. The adhesive is versatile for most of the substrates and functions normally for wet surfaces and underwater. Several characterizations are conducted to evaluate the performance of the adhesive and study the adhering mechanism. Moreover, we also use p(DMA-MEA) and LM to perform some designed underwater applications, demonstrating the potential for practical use of our research. This work will significantly enrich the applications of LM.