The chemical element gallium could be used as a new reversible adhesive that allows its adhesive effect to be switched on and off with ease
Some adhesives may soon have a metallic sheen and be particularly easy to unstick. Researchers at the Max Planck Institute for Intelligent Systems in Stuttgart are suggesting gallium as just such a reversible adhesive. By inducing slight changes in temperature, they can control whether a layer of gallium sticks or not. This is based on the fact that gallium transitions from a solid state to a liquid state at around 30 degrees Celsius. A reversible adhesive of this kind could have applications everywhere that temporary adhesion is required, such as industrial pick-and-place processes, transfer printing, temporary wafer bonding, or for moving sensitive biological samples such as tissues and organs. Switchable adhesion could also be suitable for use on the feet of climbing robots.
The principle is actually quite simple: Above 30 degrees Celsius, gallium metal is liquid, and below 30 degrees it is solid. So if a drop of liquid gallium is introduced between two objects and then cooled to less than 30 degrees, the gallium layer solidifies and sticks the two objects together. When it is time to separate the objects, the temperature is raised to transition the gallium layer to its liquid state and they can be pulled apart with a small amount of unloading force. As an adhesive, gallium works in a similar fashion to hot glue, widely used in DIY applications. The difference is that far less heating and cooling are sufficient in the case of gallium, it lifts much more easily and cleanly from the surface, it is highly repeatable, and it is electrically conductive.