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American researchers have developed a photosensitive material that hardens under the action of ultraviolet light and becomes 10 times softer when exposed to green light, and can change back and forth multiple times. This ability to change makes new materials expected to be used as special coatings in the future, but it is still far from practical.

The Massachusetts Institute of Technology has released a news bulletin saying that the new material developed by researchers at the school is a "polymer metal-organic cage". The basic unit is a cage-like molecule containing metal atoms, which is "fastened" by the polymer. Connected. This material can change between two distinct states, soft and hard. It is expected to be used as a "self-healing" coating for automobiles, satellites, robots, etc.

The research team published a paper in the British journal Nature that they added a light-sensitive molecule to the site where the polymer is connected to the metal atom. Changes in the molecule will affect the way of connection and thus change the overall structure of the material.

Under ultraviolet irradiation, the atoms in the material will form relatively large clusters, making the material harder; green light irradiation changes the photosensitive molecules, resulting in smaller clusters and softening of the material. The change process takes about 5 hours. In experiments, the new material can withstand up to seven back-and-forth changes.

According to reports, this soft-hard "switching" characteristic has brought "self-healing" capabilities to new materials. For example, cracks generated in a hard state can be repaired by melting and reorganizing the material in a soft state.

However, researchers said that this result is far from practical. One of the problems to be solved is that the metal used in the new material is expensive palladium. They hope to find cheap alternatives with the same performance to reduce costs.