An adhesive that holds tight in cold, gets stronger in heat

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Carbon nanotubes collapse to penetrate and grip a surface(Credit: Case Western Reserve University)

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Researchers have developed a new dry adhesive that not only bonds in extreme temperatures, it even gets stronger as the heat goes up. The gecko-inspired material maintains its hold in extreme cold and actually gets stickier in extreme heat.

Building on previous research, a team of engineers from Case Western Reserve University and Dayton Air Force Research Laboratory created a double-sided tape made of carbon nanotubes that they claim would lose no traction whether applied to cold liquid nitrogen or hot molten silver.

The nanotubes that make up the adhesive are vertically aligned and bundled into nodes similar to the microscopic hairs on a gecko's foot pads that allow it to walk up walls. A number of other adhesives and grippers have been derived from the same inspiration, but this new invention has some notable qualities.

Most commercial tapes you might buy in a store lose their stickiness as they freeze or heat up, but the new carbon nanotube adhesive stayed just as strong down to -320 degrees Fahrenheit (-196 Celsius), doubled strength at 785 degrees Fahrenheit (418 C) and increased its grip six-fold at 1,891 (1,033 C) degrees.

The researchers used a high-powered scanning electron microscope to observe what gives the adhesive its unusual increasing strength. They found that the nanotubes collapse into web-like structures that increase the contact surface area with a material, in turn enhancing the "sticky" van der Waal's forces. Increases in temperature can make the surface the adhesive is applied to more rough, allowing the nanotubes to penetrate deeper into the irregularities and hold even tighter.

"The dry adhesive doesn't lose adhesion as it cools because the surface doesn't change," explains Ming Xu, a senior research associate at Case School of Engineering and visiting scholar from Huazhong University of Science and Technology. "But when you heat the surface, the surface becomes rougher, physically locking the nanotubes in place, leading to stronger adhesion as temperatures increase."

The resilience of the new adhesive could make it especially useful in space, where temperatures can swing by several hundreds of degrees between the shade and direct sunlight. It also conducts heat and electricity, adding to its potential utility.

"This adhesive can thus be used as connecting materials to enhance the performance of electronics at high temperatures," said study author and Case Western Reserve professor Liming Dai said. "At room temperature, the double-sided carbon nanotube tape held as strongly as commercial tape on various rough surfaces, including paper, wood, plastic films and painted walls, showing potential use as conducting adhesives in home appliances and wall-climbing robots."

The research is published in the latest issue of the journal Nature Communications.

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