Taking inspiration from the way sea cucumbers can strengthen their exterior when in danger, scientists in Germany have developed a novel wafer-thin paper material that can transition from firm to soft via an electrical switch. The researchers envisage a number of uses for their creation, including adaptive damping materials that harden when subjected to heavy loads.
The material was developed by scientists at Johannes Gutenberg University Mainz and the University of Freiburg, who used cellulose nanofibrils as their starting point. These can be extracted from the cell walls of trees and, because they are finer than the microfibers used to create standard paper, create a glass-like paper that is completely transparent, while also being stiff and strong.
By subjecting their wafer-thin "nanopaper" to an electrical current, the scientists are able to heat it up and break apart cross-linking points in the material at a molecular level. The higher the voltage, the more cross-links are busted and the softer the material becomes. Conversely, this process can be reversed by cutting the electrical supply.
"This is extraordinary," says Professor Andreas Walther, who led the research team. "All the materials around us are not very changeable, they do not easily switch from stiff to elastic and vice versa. Here, with the help of electricity, we can do that in a simple and elegant way."
While already impressive, the team is eyeing further improvements for its adaptive material. Where it now relies on an external power source for the electrical current, the scientists are hoping to develop a version with its own onboard energy storage. This would enable the reactions to be initiated internally and without manual intervention, like when the material is overloaded beyond a certain threshold and it needs to absorb some of the energy.
"Now we still have to flip the switch ourselves, but our dream would be for the material system to be able to accomplish this on its own," says Walther.
The research was published in the journal Nature Communications.