New York: Engineers from the University of Rochester have developed a new class of rubber-like material that not only self-stretches upon cooling but also reverts back to its original shape when heated - all without physical manipulation.
The material is like a shape-memory polymer because it can be switched between two different shapes.
"However, 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," explained Mitchell Anthamatten, associate professor of chemical engineering.
The team built on the success of a recently developed polymer that can also stretch when cooled.
The other polymers need to have small weights attached in order to direct the shape to be taken.
That is not the case with the Rochester polymer because Anthamatten's team "tricked it into thinking" a load was attached.
To carry out their strategy, the researchers introduced permanent stress inside the material.
"The stress we built into the network takes the place of the load and enables the material to 'remember' the shape it will assume when it's later cooled without a load," Anthamatten noted.
The material was stretched with a load attached to give it the desired shape.
The new material can be applied to a number of areas in which reversible shape-changes are needed during operations, including biotechnology, artificial muscles and robotics.
"The next step is to optimise the shape of the polymer material and the energy released during the process," Anthamatten concluded.
The findings were published in the journal ACS Macro Letters.