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Reusable adhesive liquifies and solidifies at room temperature due to light alone
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Reusable adhesive liquifies and solidifies at room temperature due to light alone

This material, developed by AIST, is an organic substance where the adhesion strength can be varied repeatedly. This is achieved simply by shining light on the material, without heating or cooling it.

When the material has solidified, it's yellow, but if it's illuminated with UV light, it gradually liquefies and becomes orange. If you shine green light on the material, it hardens again, and reverts to yellow. This is the first example of a solid-liquid transition caused by light alone, deliberately and reversibly, in a single substance.

"This isn't a reaction where new bonds form and break. This material uses what's called an isomerization reaction, where the shape of a compound changes reversibly. Because the reaction is caused by light, it's also possible to attach this material in certain places only, and remove it in other places."

"The reaction depends on the amount of light. Here are two glass plates with an adhesive layer between them, about 10 microns thick. Under these conditions, using 80 mW light, the material liquefies in about 3 minutes. The light's wavelength must be in a specific range, from 365 nm to 385 nm, and it's better if other light is minimized. Now, with this green light, the material hardens in 1-2 minutes. Even with the light in a place like this, the material does harden, but it's most sensitive to this green wavelength."

The material's current adhesive strength is 50 N/cm2, which is enough to suspend a 5 kg object from an adhesive surface 1 cm square. It's about the same strength as double-sided adhesive tape.

"The adhesive strength is still weak, so we'd like to improve it. We'd also like to change the color, which isn't very attractive."

"For example, in a manufacturing process, if you want to hold something in place temporarily, there are adhesive materials that can be peeled off. But that imposes a load on the objects. Using this type of material, things can be stuck together and separated without using force. So, we think it might enable new kinds of manufacturing process."

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