Some years ago I accidentally discovered a polymer-based adhesive that allowed the irreversible joining of two metal strips. Amazingly, the adhered juncture was stronger than the metal itself, but of course the bond was permanent and could not be undone.
I haven’t thought much about adhesion in the intervening years, but a new publication from the GM Research & Development Center has rekindled my interest.
As is often true with new materials, nature was a source of inspiration, in this case the lowly gecko, whose footpads are notoriously sticky. Luckily, the bonding is reversible, or the poor lizard wouldn’t be able to go anywhere.
Governing this reptilian interaction are noncovalent van der Waals forces, which are actually quite weak on the molecular level. Ruomiao Wang and Tao Xie reasoned that H-bonding could create a stronger adhesion, but still be reversible because of the noncovalent nature of such bonds (Langmuir, DOI: 10.1021/la9046403, published online 2 February 2010).
The material of choice was a highly crosslinked epoxy polymer with added H-bond acceptor and donor sites. When the material is heated to cure the glue, a tight bond is formed. When heated again, the adhesion releases because the hydrogen bonds that are the source of attraction are broken.
What uses could be imagined for an adhesive that is sturdy under normal operating conditions but reversed on demand? How about reconfigurable rooms or buildings. Perhaps adding extra bumpers to automobiles in slippery conditions. Maybe museums could create exhibits with priceless works that make the objects secure but accessible, yet easily swapped when the next exhibit comes along.
I bet creative readers can come up with all manner of exotic ideas for a reversible adhesive.