New types of adhesives could be used to make remarkably reusable office tape, sticky notes or even bandages, according to chemical engineers at the Indian Institute of Technology in Kanpur. The new materials are almost as strong as normal adhesives, but they can be peeled off and stuck back onto an object repeatedly without losing much of their stickiness.
Peel back an ordinary piece of tape, and some of the sticky stuff will be left behind. Even worse, the used tape may be covered in gunk that won't come off. That's because most adhesives are tacky, gooey, viscous substances. They can be pulled off of their backing or ruined by flakes of paint and dust.
Researchers have come up with new adhesives designed to avoid those problems. They report their findings in the journal Langmuir, a publication of the American Chemical Society.
"There are two layers in this adhesive tape," explained Ashutosh Sharma, a chemical engineering professor who led the study. One of the layers is a "slimy goo core topped with a much thinner nonsticky elastic skin, which is easy to clean."
The thick layer of goo is what gives the new adhesive its stickiness, and the thin skin protects the goo from mixing with dirt or coming off of its backing.
Oddly enough, both the sticky goo and the nonstick elastic goo are made from the same chemical, a substance called polydimethyl siloxane, a rubbery polymer that is made from long chains of silicon and oxygen. The main difference between the two materials is that the thin skin has a lot of links between neighboring chains, which makes it more rubbery.
To find out just how reusable they are, graduate student Sandip Patil made some tape using the new adhesive. He attached it to a piece of glass and pulled it off of the glass repeatedly. It didn't leave any sticky residue behind, and it adhered to the glass almost as strongly as normal tape. If the tape got dirty, he could make it work again by cleaning the dirt off with another piece of tape.
In their journal study about the adhesives, Sharma and Patil say the new materials can be put into standard tape-making machines. So it would be easy for a tape company to start using it. The researchers also say they can fine-tune the stickiness of the tape by increasing or decreasing the thickness of the elastic layer.
Since these adhesives have two distinct layers, they're more complicated than the single-layer goo that you would find in a standard roll of office tape. But they're not nearly as complicated as some of the sticky things that nature has made. Gecko feet and insect toes are far more complex. By mimicking those natural stickers, engineers may someday make even better glues.