Researchers at the University of Rochester have developed a special shape-shifting polymer that can lift loads over 1,000 times its own weight. Thanks to its incredibly high elasticity, the new material is capable of returning to its original shape, when triggered by heat. Although still in the early stages of development, the technology has a wide range of potential applications, including highly-specialized medical devices that function according to your body heat, and also clothes that can automatically shrink for a snugger fit.
Led by Mitch Anthamatten, a professor of Chemical Engineering at the University of Rochester, the team has created a versatile polymer that can easily retain a temporary stretched shape, until it is triggered by heat to contract to its normal shape. During the process, however, the stored elastic energy enables the material to lift weights nearly 1,000 times heavier. Speaking about the research, recently published in the Journal of Polymer Science Part B: Polymer Physics, Anthamatten said:
Tuning the trigger temperature is only one part of the story. We also engineered these materials to store large amount of elastic energy, enabling them to perform more mechanical work during their shape recovery.
Central to the technology is the mechanism by which the shape-shifting polymer controls the crystallization process that takes place when it is stretched or cooled. According to the scientists, when the material undergoes deformation, its polymer chains are locally stretched, with small parts of the polymer aligning themselves in the same direction to form crystallites. As the crystallites grow in number, the temperorary shape becomes more stable, thus making it difficult for the material to return to its original, undeformed shape.
To make the polymer heat-sensitive, the researchers included special molecular linkers into the design, for the purpose of connecting the individual polymer strands. As the team points out, these linkers inhibit (though not completely stop) the crystallization process that a material goes through when stretched. In order to set a specific ‘melting point’ that triggers the shape change, the scientists tinkered with the number, types and distribution of the linkers. This allowed them to adjust the stability of the polymer when deformed. Anthamatten added:
Our shape-memory polymer is like a rubber band that can lock itself into a new shape when stretched. But a simple touch causes it to recoil back to its original shape.
According to the team, heating the material to around 35 degrees Celsius, which is slightly less than our body’s normal temperature, actually causes the crystallites to break apart, thus allowing the polymer to revert to its initial shape. What is more, it can perform large amounts of mechanical work while returning to its permanent shape, thanks to its specially-engineered polymer networks that allow it to store as much of elastic energy as possible. The team said:
Nearly all applications of shape memory polymers will require that the material pushes or pulls on its surroundings. However, researchers seldom measure the amount of mechanical work that shape-memory polymers are actually performing.
Laboratory testing has revealed that it is capable of lifting nearly 1,000 times its mass. For instance, a shoe laced-size polymer, weighing only around one gram, can easily lift a one-liter bottle of soda. Described as “plastic with a brain, and some muscle”, the technology, the scientists believe, could have a number of applications, including body heat-controlled medical devices, artificial skin, sutures, and even self-fitting clothing.
Source: University of Rochester