The picture shows a polymer designed by a chemist at the Massachusetts Institute of Technology that is both light-sensitive and reversibly switchable from a large structure to a smaller blue object.
Researchers at the Massachusetts Institute of Technology (MIT) have designed a polymer material that changes its structure to respond to light, transforming it from a hard substance into a flexible substance that can heal itself when damaged.
Jeremiah Johnson, an associate professor of chemistry at the Massachusetts Institute of Technology, is a member of the MIT's Koch Institute for Integrative Cancer Research and the leader of the Polymer and Soft Matter Project Research Group. He said: 'You can switch the state of the material back and forth, and in each state, even if it consists of the same composition, it is like a completely different material.'
Johnson suggested that This material consists of a polymer attached to a photoreceptor molecule that can be used to change the chemical bonds formed inside the material. Although this material can be used to coat objects such as cars or satellites, allowing them to heal after damage, these applications are far away in the future.
The first author of the paper published in Nature is Yu Wei Gu, a graduate student at the Massachusetts Institute of Technology. Other authors include Eric Alt, MIT graduate student, Adam Willard, assistant professor of chemistry at the Massachusetts Institute of Technology, and the University of South Florida. Heng Wang and Xiaopeng Li.
Many of the properties of a polymer, such as its hardness and expansion capacity, are governed by its topology, that is, how the composition of the material is aligned. Typically, once the material is formed, its topology cannot be reversibly altered. The rubber ball remains elastic and does not become brittle without changing its chemical composition.
In this paper, Johnson and his colleagues want to create a material that has never been seen before, which can be reversibly switched between two different topological states. They realize that they have designed a polymer a few years ago. Metalorganic cage material polyMOCs, this material is a promising candidate for its realization. PolyMOCs are formed by connecting a metal through a flexible polymer to form a cage structure.
The researchers made these materials by mixing polymers attached to groups called ligands, which can bind to metal atoms. Each metal atom (in this case, metal palladium) can be bonded to four ligand molecules to form rigid cage clusters with different palladium to ligand molecular ratios. These ratios determine the size of the cage clusters.
In this new study, the researchers plan to design a material that can be reversibly switched between two cages of different sizes: one with 24 palladium atoms and 48 ligands, one with 3 palladium atoms and 6 Ligand molecules.
To achieve this goal, they incorporated a photoactive molecule called DTE into the ligand. The size of the cage is determined by the angle of the bond between the nitrogen molecule on the ligand and palladium. When the DTE is exposed to ultraviolet light, it Forming a ring in the ligand increases the angle at which the nitrogen bonds to the palladium. This causes the cluster to rupture and form larger clusters.
When the researchers emit green light on the material, the ring is broken, the bond angle becomes smaller, and smaller clusters are formed. This process takes about five hours to complete. The researchers found that they could perform seven reversals. At each reversal, there was always a small portion of the polymer that could not be reversed, eventually leading to material separation.
When the material is in a small cluster state, it is 10 times more dynamic and more dynamic under normal conditions. Johnson says: 'They can flow when heated, which means you can cut them and in mild heating conditions Self-healing. '
This approach overcomes the problem that usually occurs with self-healing materials, ie they tend to be relatively weak in structure. In this case, the material can be switched between a softer self-healing state and a more rigid state.
In the research, Researchers use polymer polyethylene glycol (PEG) to make materials that they believe can be used with any kind of polymer. Potential applications include self-healing materials, and although this method is widely used, palladium, a rare and expensive metal, must be replaced by a cheaper alternative.
"Anything made of plastic or rubber can be repaired if it is damaged," Johnson said. "You don't have to throw it away. Maybe this method will give the material a longer life."
Another possible application for these materials is drug delivery. Johnson believes that it is possible to encapsulate the drug in a larger cage structure and then expose it to green light to open and release it. Applying green light can also re-do the drug. Captured, providing a new method for reversible drug delivery.
Researchers are also working to create materials that reversibly transform from solid to liquid, and use light to create a flexible and rigid pattern within the same material.