AKRON—Water traditionally has been adhesion's nemesis. But new research from the University of Akron shows that water may actually help to improve adhesion under controlled conditions.
Ali Dhinojwala, distinguished W. Gerald Austen endowed chair and H.A. Morton Professor at the University of Akron's School of Polymer Science and Polymer Engineering, led a research team that included Lars Pastewka from the University of Freiburg, Anirudha Sumant from Argonne National Laboratory and Tevis Jacobs from the University of Pittsburgh.
Traditionally, the presence of water disrupts the molecular bonds necessary for effective adhesion. Water does this by clinging to surfaces and getting trapped in the surface roughness.
What the team found, however, is that water could increase adhesion by nearly four times during detachment. Analytical models and surface-sensitive spectroscopy showed the water is trapped in nanometer-sized pockets.
"Contrary to expectations, the presence of water during contact formation initially disrupts adhesion by preventing molecular contact over nearly half of the surface area due to trapped water molecules," a University of Akron news release said. "Moreover, the energy required to deform the elastomer and conform to the surface roughness is significantly increased in the presence of water, further reducing initial adhesion."
"It's hard to make contact under water because extra energy is required to squeeze out the water and you can't remove it entirely," Jacob said in a statement. "But we were very surprised to see that the same trapped water that makes it hard to push two surfaces together, also makes it significantly harder to pull the same surfaces apart."
The implications of the findings are great, according to UA. Applications include biomedical instances such as bandages, health monitoring sensors for moist skin and advanced adhesives that could replace sutures.
"The insights gained into leveraging surface roughness and material properties could revolutionize industries worth billions of dollars globally," the news release said.
Dhinojwala's graduate student, Nityanshu Kumar, performed the underwater experiments and developed the models that explained the results. Argonne National Lab chemically prepared the rough surfaces and they were characterized down to the atomic scale by the University of Pittsburgh. Simulations of the separating interface were conducted at the University of Freiburg. The team said the investigation was only possible because of the complementary expertise of the collaborative team.
