Scientists have challenged previously accepted beliefs with their research indicating that water may actually aid adhesion. This discovery has particularly useful implications in the biomedical field, such as for bandages, moisture-sensitive health monitoring devices, and innovative adhesives that could serve as alternatives to sutures. The knowledge gained from examining surface roughness and material characteristics could significantly transform industries valued in the billions worldwide.
Researchers from the University of Akron and the University of Pittsburgh have revised longstanding beliefs in a new study demonstrating that water can enhance adhesion.
Dr. Ali Dhinojwala, the 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 team that discovered a major breakthrough — that water can surprisingly improve adhesion in controlled settings. This finding was published on August 7 in Science Advances.
The ramifications of this study are significant, especially for biomedical uses like bandages, sensors for monitoring health on moist skin, and new types of adhesives that could replace traditional sutures. The research provides insights into how to utilize surface roughness and material properties, setting the stage for a potential revolution in valuable industries across the globe.
Everyday situations such as driving on wet roads or using adhesive tape on damp skin highlight the difficulties associated with achieving strong adhesion on wet, rugged surfaces. In the past, water was typically regarded as a barrier, breaking down the molecular bonds necessary for effective adhesion. Water often accumulates on surfaces and gets trapped in their roughness, complicating the adhesion procedure.
In a noteworthy advancement, Dr. Dhinojwala’s team — which included Dr. Tevis Jacobs from the University of Pittsburgh, Dr. Lars Pastewka from the University of Freiburg, and Dr. Anirudha Sumant from Argonne National Laboratory — uncovered their findings in a study focused on measuring how a soft elastomer bonds to accurately engineered rough surfaces. This revealed a complicated relationship between water, surface roughness, and adhesion behavior.
Dr. Dhinojwala and graduate student Nityanshu Kumar conducted pioneering underwater experiments and created models to clarify their findings. The rough surfaces were chemically modified at Argonne National Lab and analyzed at the atomic scale at the University of Pittsburgh. Simulations regarding the separating interface were carried out at the University of Freiburg, made possible through the complementary skills of this collaborative team.
Unexpectedly, water presence during the initial contact detracted from adhesion by blocking molecular contact across nearly half the surface area due to water molecules getting trapped. Additionally, water significantly raised the energy required for the elastomer to deform and match the rough surface, leading to a decrease in initial adhesion.
Interestingly, while water disrupts adhesion when surfaces first make contact, it can enhance adhesion nearly fourfold during the detachment phase. Analytical models and surface-sensitive spectroscopy showed that water becomes trapped in tiny pockets at the nanoscale. “It’s challenging to establish contact underwater since additional energy is needed to expel the water, and you can’t completely remove it,” explained Dr. Jacobs. “However, we were astonished to discover that the very trapped water that makes it difficult to press two surfaces together also significantly impedes the process of pulling them apart.”
“These results contradict the conventional notion that water always impairs adhesion,” remarked Dr. Dhinojwala. “By understanding how water interacts with surface texture, we can potentially utilize roughness to boost adhesion. This is akin to how geckos use their toe pads to scale damp surfaces.”
Dr. Dhinojwala’s team plans to continue refining these discoveries to create practical applications that take advantage of the unexpected benefits water offers in adhesion science.
