Researchers have developed a new type of polymer that is able to shape shift at particular times autonomously, without any input.
This is the first time that scientists have been able to create a material that can do this, as shape-changing materials usually require an outside trigger, such as light. To demonstrate this impressive feat, the team have created an impressively realistic looking flower that opens and closes on its own.
The study was led by Professor Sergei Sheiko of the University of North Carolina and published in the journal Nature Communications.
The polymer works by having a mixture of different types of bonds. The first are permanent bonds that determine the final shape of the material, as they act a little like springs, snapping back to the desired configuration. It is the dynamic, or reversible bonds, however, that control the rate at which the polymer changes shape. These are in turn controlled by a couple of different factors, and it is the number and positioning of these that dictate the specific timings.
“One [factor] is the strength of the individual bond – or the energy of dissociation of the individual bond. The other is the concentration of these bonds,” Professor Sheiko told BBC News. “There is a third parameter: several individual hydrogen bonds (dynamic bonds) can form a cluster. This cluster of hydrogen bonds can then form stronger cross-links.”
By tightly managing where these bonds are on the polymer, and when they will break, the researchers have been able to create the material that alters its shape at a specific time. While they found it difficult to create a complex shape-shifter from one piece of polymer, by adding together multiple components, which were each set to a different time, they were able to make objects change shape in sequence, as seen with the individual petals opening on the flower.
“We wanted to make the concept more explicit. So there are plenty of examples in nature, like flowers, which change their shape with time,” Professor Sheiko said to BBC News. “One of the advantages of our technology is that you can assemble a complex shape of individual pieces like these petals. Usually, shape memory materials are just made up of one chunk that changes shape.”
Shape-shifting materials are nothing new, but they usually need some sort of external trigger, such as light or heat. This newly developed polymer has, however, been developed so that it in effect it has its own internal clock, changing its shape at certain times. This could have all sorts of applications, for example for medical implants or drug delivery systems, where traditional shape-shifting polymers fail due to the dark, stable environment of the body rendering external triggers useless.
