Part sponge, part playdough, not quite a liquid and but not really a solid, this new material exhibits some crazy properties. It can be compressed and bounce back like a sponge, it can be cut into pieces and it will heal itself, stitching itself back together and still self-stiffen.
Known as self-adaptive composite (SAC) it is made of mostly micron-scale rubber balls that cling to one another forming a solid matrix.
Other self healing materials behave like liquids whereas SAC performs more like a solid. “We wanted a biomimetic material that could change itself, or its inner structure, to adapt to external stimulation and thought introducing more liquid would be a way,” said one of the researchers, Alin Cristian Chiparaf rom Rice University. “But we wanted the liquid to be stable instead of flowing everywhere.”
To achieve this SAC two polymers are mied with a solvent, heated until the solvent evaporates, leaving a porous mass of gooey spheres. The result are tiny polyvinylidene floride (PVDF) balls coated in polydimethylsiloxane (PDMS).
“The sample doesn’t give you the impression that it contains any liquid,” said material scientist, Jun Lou. “That’s very different from a gel. This is not really squishy; it’s more like a sugar cube that you can compress quite a lot. The nice thing is that it recovers.”
The researchers say the final mixture can be changed based on how you want the SAC to behave and is easily manufactured although it is currently only being made in 150 millimeter containers for use in the lab.
“Gels have lots of liquid encapsulated in solids, but they’re too much on the very soft side,” said one of the team, Pulickel Ajayan. “We wanted something that was mechanically robust as well. What we ended up with is probably an extreme gel in which the liquid phase is only 50 percent or so.”
Check out the video from the researchers about their SAC.