LightTight

Loctite Blue glue is remarkable stuff. In the presence of oxygen it is a liquid, and it only sets hard when oxygen is excluded. This means that when you put it on a bolt thread it is easy to screw the bolt onto its nut. But once the bolt is tight (which excludes the oxygen) the glue locks up, preventing the thread coming undone.

Even cleverer, the reaction is reversible. Thus, when you loosen the thread a bit with a spanner, the ingress of the air releases the bond, and the bolt can easily be undone the rest of the way. Rather neatly, the bottle in which the glue is sold is permeable to oxygen, so the glue stays easy to pour.

There are often photochemical reactions that are equivalent to this type of reversible bonding. So how about a glue that sets solid in the dark and is liquid in the light?

You would paint it on a surface, where it would stay happily liquid (well, it would till dusk...). But when you put down the other surface to be stuck on top of it, the glue would instantly set solid as the shadow fell, holding both fast.

If one of the two items to be stuck were translucent, but covered (except for the sticking surface) in an opaque paint, the glue would still work. But you could release it simply by opening a window in the opaque paint. It would be possible to set up all sorts of complicated simultaneous sticking and release mechanisms that were worked by allowing light in and excluding it.

It might even be possible to have the material respond to different wavelengths if the no-stick chemistry were only triggered by photons of a specific energy. Different coloured lights could then be used to release different bonds.

You could also have an electric release mechanism: simply bury LEDs in one of the surfaces...