Products designed with temporary adhesives that don’t hold forever — such as sticky notes, painter’s tape, and bandages — still require some level of force to be removed, meaning there’s always the risk of damaging paint on a wall or painfully losing some body hair. But what if glue simply vanished into thin air when it was no longer needed? It’s an idea that researchers at Dartmouth College have made a reality.
The glues used to create products with temporary adhesion are made from long chains of molecules known as polymers that produce strong bonds as they get entangled. Permanent glues use polymers that are very effective at tangling to create incredibly strong and near-inseparable bonds, whereas the polymers used on products like masking tape are less effective at getting all tangled up, allowing the bonds to be more easily broken using mechanical force. But that force that can potentially result in unwanted damage.
The Dartmouth researchers have instead focused on a class of adhesives known as molecular solids, where instead of tangled chains, the molecules stack atop one another and are held together by different types of intermolecular forces, depending on their chemical makeup. These materials exist as crystals (dry ice, for example, is considered a molecular solid) and their structures are sublimable, which means they can transition directly from a solid to a gas without having to become a liquid first.
In a new paper published in Chemistry of Materials, the Dartmouth team reveals an expanded list of molecules that can be used to create adhesives based on molecular solids that are not only strong and easy to create, but they can be easily removed without the need for other chemicals or excessive force. When heated and placed inside a vacuum, the glues simply sublimate into a gas, releasing their bonds and leaving no trace behind.
To test one of their glue alternatives in the real world, the team applied 300 milligrams of it to a pair of aluminium plates, bonding them together. The adhered metal plates were then connected to carabiners and straps and were successfully able to support the weight of a researcher weighing 175 pounds (pictured above). The metal plates weren’t tested to failure, but the researchers are confident the new adhesives could support a minimum of 227 kg.
Most of us probably don’t want to crank the thermostat and pump all the air out of our offices every time we want to remove a sticky note, so molecular solids aren’t yet a practical replacement for everyday adhesives — tearing off a Band-Aid isn’t going to get any easier in the near future. Where the new approach to polymer-less adhesives is going to be a welcome innovation is in manufacturing technologies, such as semiconductors, which require components to be temporarily bonded together as they’re assembled. Using mechanical force is problematic, given how sensitive electronics can be, and solvents are an added cost. Removing them from the equation could have broad implications for the industry.