shape shifting

Heat causes things to expand – we have been taught that since an early age. You can see the concept in practice via the metal expansion joints on a bridge. But what if we could create a material that contracts when heated. Researchers at the University of Rochester though have developed a substance that does just that. What actually is happening is that the polymer is returning to its original shape; if you stretched and twisted it and then exposed it to heat, the material would shrink and straighten to its original form. Think of it as a rubber band that holds its shape until receiving an instruction set to release the stored elastic energy, returning the polymer to its original form. By storing its new shape as elastic energy, the material is capable of lifting 1,000 times its weight when in contracts! The process of how this is achieved is pretty clever. When shape-memory polymers are cooled or stretched, small segments of the polymer align in the same direction; these are called crystallites. These crystallites make it increasingly difficult for a material to return to its original form. Researchers found that by using molecular linkers to connect polymer strands they could inhibit (but not stop) crystallization. By heating these linkers to their melting-point, the crystallites break apart and the material returns to its original shape. The polymer can be customized to respond to different temperatures, including body heat, by adjusting the number of links and substances used.