As a rule, absorbent and liquid-repellent materials are quite different in structure, which determines their properties. A typical example is the myriad of tiny hairs on the body of a gecko, which repel water. On the other hand, specially treated cotton fibers, on the other hand, are hygroscopic. Thanks to millions of tiny pores, they collect moisture from the air and turn it into a liquid.
An international team of researchers from the universities of Vienna and Zurich has created a material that can function in both "modes". Switching between repulsion and liquid absorption is accomplished by applying electrical voltage.
The change in the "relation" of a material to water occurs at the nanoscale. The higher the level of the applied voltage, the stronger the "sticking", that is, the surface structures of the material are tightly closed and do not allow water to pass through. However, as soon as the tension is reduced, they begin to open slightly, letting the liquid inside.
Adjustment of the “sticking” level is made possible by a nanoscale grid of single-layer boron nitride (“white graphene”) grown on a rhodium substrate. A honeycomb structure was created with a ridge depth of about 0.1 nm and a ridge of 3.2 nm. The applied stress flattens the mesh and changes the angle of contact between the water molecules and the surface until they completely lose their adhesion to the surface.
Scientists intend to use their invention in biology to control cells at the microscopic level, as well as to create microcapillary pumps.