As bendable screens continue to appear in more products, we’ll need more resistive adhesives to keep them together, says Ruobing Bai, a Northeastern University professor of mechanical and industrial engineering.
Folding smartphones — once thought to be the stuff of science fiction — are increasingly becoming commonplace. Yet their long-term reliability continues to be a problem, especially at the component level.
Think of the stress a device like Samsung’s Galaxy Z Fold6 goes through every time its inner folding screen is opened and closed. That can take a serious toll on the phone’s structural integrity.
One of the key materials used to hold these devices together is tape. But as it stands, the tapes on the market, which were originally designed for more static-loading conditions, “are terrible for holding their bonding under cyclic loads,” explains Ruobing Bai, a Northeastern University professor of mechanical and industrial engineering. They weaken on repeated use, causing screen fractures, which ruin devices.
These “soft sticky adhesives” are used in more than just consumer electronics. They are also featured in products ranging from Post-it Notes to wound dressings, Bai explains, and they are in serious need of an upgrade to keep up with the proliferation of wearable devices and bendable screens.
Taking advantage of a CAREER Award grant from the National Science Foundation, Bai hopes to do just that.
More specifically, Bai will investigate the mechanical failure points of these adhesives, develop a new framework to understand the fatigue mechanisms behind them, and create a new class of sustainable adhesives that are switchable to an non-adhering state upon heating.
This research is at the heart of Bai’s work at Northeastern. For years, he has focused on understanding how materials form and fracture. At his research lab at the Mugar Life Sciences Building, Bai and his students conduct both real-world and simulated experiments to gain a deeper understanding of the science of these material systems, primarily polymers.
With this project, Bai and his team — which will include a collaboration amongst 3M, Northeastern’s Young Scholars Program, Northeastern’s Center for STEM Education and Northeastern’s Office of Undergraduate Research and Fellowship — will synthesize and fabricate the materials they plan to test from their powdery scratch, Bai explains.
With those tapes developed, the team will conduct a series of peel-and-pulling tests both physically and through computer-generated simulations.
Once the team has an understanding of the different mechanisms behind these fractures, they plan to develop a new class of switchable adhesives using relatively new materials called liquid crystal elastomers, which are thermally responsive.
“It can change its properties dramatically under heat or cool, and it’s reversible,” he says. “It gives us the opportunity to use this material as an adhesive,” says Bai.
There are many potential benefits that can come with the development of “fatigue-resistant switchable soft sticky adhesives,” Bai explains, from reductions in manufacturing costs and e-waste to the development of advanced robotic systems and precision health care devices.