Liquid Metal Transient State Machine

Abstract

Internally triggered motion of an object owns important potential in diverse application areas ranging from micromachines, actuator, or sensor, to self-assembly of superstructures. This lab (Sheng et al. in Small 11:5253–5261, 2015 [1]) proposed and demonstrated a new conceptual liquid metal machine style, the transient state machine that can work as either a large size robot, partial running elements, or just divided spontaneously running swarm of tiny motors. According to the need, the discrete droplet machines as quickly generated through injecting the stream of a large liquid metal machine can combine back again to the original one. Over the process, each tiny machine just keeps its running, colliding, bouncing, or adhesion states until finally assembles into a single machine. Unlike the commonly encountered rigid machines, such transient state system can be reversible in working shapes. Depending on their surface tension, the autonomously traveling droplet motors can experience bouncing and colliding before undergoing total coalescence, arrested coalescence, or total bounce. Further, the liquid metal machine can also be made as color changeable. In this sense, some transformable biomimetic soft machine which was termed as liquid metal “chameleon” has now been possible. As it was demonstrated, the fluorescent liquid metal can be manipulated into various appearances like fluorescent orange, blue, pink, or even send out fluorescence in the dark. It can realize transformation and discoloration by splitting and merging among different colors. If subject to electrical stimulation, such colors would transform from fluorescence into metallic color. These findings are expected to help design future color changeable machines and mold unconventional robot that could automatically transform among different geometries such as a single or swarm, small or large size, assembling and interaction including color, etc. It refreshes people’s basic understandings of machines, smart materials, fluid mechanics, and micromotors. In this chapter, the basic concept of the liquid metal transient state and color changeable machines will be illustrated.