Scientists at the University of Rochester recently developed a heat-activated self-stretching material that reverts between two shapes depending on temperature.
This material falls in a category known as shape-memory polymers, polymers that can change between a rigid and elastic state under a stimulus (usually thermal). According to University of Rochester associate chemical engineering Professor Mitchell Anthamatten, “…unlike other shape-memory polymers, the material does not need to be programmed each cycle — it repeatedly switches shapes, with no external forces, simply upon cooling and heating.”
Before Anthamatten and his team began work on their shape-memory polymer, another group of scientists developed their own polymer that could stretch under cooling conditions, but required small weights to properly form the shape of the polymer. Anthamatten’s technique for obtaining his polymer’s desired form under cooling conditions was much more sophisticated, involving permanent stress within the material with crosslink bonds and cooling. This technique allowed for crystallisation in the desired directions during the shape change.
The complicated crystallisation forces involved in the polymer help to reorganise the structure of the polymer chains under cooling temperatures (less than roughly 50 ˚C). The reorganisation stretches the material by over 15%.
The technique developed by Anthamatten and his team is significant not only because it eliminated the need for small weights in shape-memory polymers, but also because their polymers did not need to be reprogrammed after each cycle. The group found after several cycles of cooling and heating that the polymer kept its original state.
This material could prove invaluable to simplify the process for many medical procedures including biotechnology and artificial muscles.
“The next step,” Anthamatten says, “is to optimize the shape of the polymer material and the energy released during the process. That will be done by adjusting the type and density of crosslinks that tie the individual chains together.”