The team—Associate Professor in Mechanical Science and Engineering Seok Kim, graduate student Jun Kyu Park, and former graduate student Jeffrey D. Eisenhaure (PhD ME ’17, now with Northrop Grumman)—has proved that SMPs can retain dry adhesion properties while submerged. Their study, “Reversible underwater dry adhesion of a shape memory polymer,” was recently published by the scientific journal Advanced Materials Interfaces(Wiley-VCH).
Classified as a smart material, SMPs have the ability to manually transition between their original state and a deformed state. By manipulating the state of their SMPs, Kim and his team achieved successful adhesion to surfaces submerged in water as well as other liquid media such as oil.
“Dry adhesives, such as those inspired by gecko feet, are believed to be inadequate to achieve high adhesion to a wet or submerged surface,” Kim said. “However, this belief has been nullified because of our SMP reversible dry adhesives.”
By applying pressure to the submerged SMP in its original rubbery state, liquid can be squeezed out from the contact interface. Under sufficient pressure, the SMP then transitions to a glassy state, essentially creating a hermetic contact condition that maintains highly strong dry adhesion. However, this state is not permanent; the SMP’s shape recovery properties allow for reversal of the adhesion. Furthermore, because the SMP can transition fluently between both states, its adhesion is reusable.
The researchers found that the maximum adhesion strength of the SMP while submerged in a freshwater condition was 18 atm, which is at least 18 times larger than that of vacuum suction cups. Similar results were achieved for submersion in saltwater and oil. They performed various experiments to explore the applications of their SMPs—for example, they used the adhesive to attach a hook to a wet wall. Once the SMP had adhered, they were able to hang a loaded backpack on the hook without experiencing any weakness in the adhesion.
“The next step for this technology will be to further explore SMP adhesive systems to enable reversible adhesive grippers.”
Kim earned his bachelor’s degree in mechanical engineering from Pohang University of Science and Technology in 2000, followed by his master’s degree in mechanical and aerospace engineering from UCLA in 2005 and his PhD in mechanical engineering from Carnegie Mellon in 2009. He joined the MechSE Department in 2011, and was a recipient of the prestigious NSF CAREER Award in 2014, the ASME Chao and Trigger Young Manufacturing Engineer Award in 2015, and the Young Investigator Award from the Korean-American Scientists and Engineers Association in 2015.