Light-sensitive polymer materials quickly transform from hard to soft

Researchers have designed a new polymer material that can change its structure based on the light source received, to move from hard to soft or self-healing if damaged.

The team at the Massachusetts Institute of Technology (MIT) is building a new material that can change the form of matter quickly from hard to flexible, like turning into another material.

'Although made from the same ingredients, our new material has many special abilities, not only transforming itself, but also restoring itself if damaged', Jeremiah Johnson, Chemistry professor at MIT and research leader, said.

This material includes light-sensitive molecules used to change the internal structure of the material. Johnson said the material could be used to coat cars or artificial satellites because of its self-healing properties when damaged.

The molecular structure of polyMOC, the material that can transform itself from hard to flexible.(Photo: Nature).

The structure is easy to change

Many characteristics of polymers such as hardness and elongation are controlled by internal structure. Normally, a material when created will not be able to change these structures, leading to its properties being unchanged. For example, one cannot crunch a rubber ball without changing its chemical composition.

The team wants to create reversible materials and change this structure to quickly switch between two different forms. This work has never been done before.

Johnson and his colleagues have found a metal-organic polymer or polyMOC , a good candidate for the material they are looking to create. PolyMOC is made up of metal-like structures but connected together by flexible polymer bonds.

The new material was created by the team by mixing traditional polymers with polyMOC, creating a molecular group that can be bonded to a metal atom. Metal atoms used are palladium that can bind to four other atoms in the other group of molecules and form a sure ratio for the new material.

However, this process cannot take place in external natural conditions. The team used a light-sensitive molecule called DTE that combined with the linked molecules. When DTE is exposed to ultraviolet light, it creates a circle outside the molecular group. Nitrogen atoms are created and linked to palladium, causing molecular groups to separate and form larger groups.

When projecting different types of light, the material changes itself to a new form.(Photo: MIT).

Next, when the green light is illuminated, the molecular groups break apart and then rejoin into smaller groups and change the overall structure of the new material. This process takes 5 hours to perform and each polyMOC material can only be performed 7 times. After each execution, there is a small amount of polymers that cannot be bonded, making molecular groups separate and permanently apart.

'When molecular groups are shrunk, the material will be 10 times softer. At that time, even if we melted and cut off, it would restore itself with strong molecular bonds, and this is the material's self-healing properties , "Johnson said.

Other substances that are capable of self-healing often have a weak structure. But polyMOC is a solidly structured material that can change state and recover itself when damaged but retains a solid molecular structure.

Materials self-healing

In addition, the team also used polyethylene polymer glycol (PEG) to create this new material. This polymer has a self-healing nature when scratched or cut off, which is expected to be applied to many heavy industries in the future. However, scientists will change palladium because this is a rare and expensive metal.

In the future, this material will be widely used in industry because of its adaptive properties.(Photo: MIT).

'Looking further, when applying this material to a plastic or rubber bottle, they will recover to their original state. This will make plastic bottles less likely to be removed after use, thereby reducing part of plastic waste, ' Johnson said.

This material is currently being studied in the laboratory, has not been released to the public nor commercialized. The team hopes to improve more to increase the state of change and self-recovery, to be widely applied in industries in the future.