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