Researchers at Rice University have found a way to create a SAC, Self Adaptive Composite material, that shows characteristics of a liquid and a solid - at the same time!
You can split a liquid by pouring a part in another container and then you can pour it back all together with the result that the splitting will be gone. The liquid molecules will mix back again as if they have never been separated. This does not happen with a solid. If you split (break) a solid you will have to use some glue to recreate the original solid and even then you will still see the junction between the two parts.
What researchers at Rice managed to do is to create a material that looks, and feels, as a solid, that you can split in pieces and then recompose obtaining an object that does not show any seams.
Additionally, if you have a solid, you can compress, squeeze, it whilst that is not possible if you have a liquid. The new material they created, on the contrary, can be compressed.
This is made possible by the structure of the material. It consists of tiny beads made of polyvinilydene fluoride filled with a viscous liquid (polydimethylsiloxane) that is also present between the spheres working like a glue.
This merging of solid and liquid characteristics is quite amazing and shows the progresses being made in material science.