GOALI/Collaborative Research: Designing Structures to Enhance Friction of Rubbery Materials

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Friction of rubbery materials against a stiff surface is of great practical importance in many applications. For example, it determines the performance and efficiency of tires, windshield wipers, and seals. Much of the previous work on control of their friction mechanisms has either varied surface chemistry or altered properties of the rubber itself. Recent research on biological attachment devices has shown how adhesion of rubbers can also be strongly enhanced by design of their near-surface architecture, but usually their sliding friction is reduced rather than increased. The principal goals of this Grant Opportunity for Academic Liaison with Industry (GOALI)project are to investigate surface architectures for enhancement of sliding and static friction against rough and smooth surfaces. The target application is improving friction of tires, and the planned research requires work on design & theory, fabrication, and testing under realistic constraints and conditions. For this reason, the project is a collaboration between two university labs (at Cornell and Lehigh) and an industrial researcher at Michelin North America. The Lehigh group is responsible for fabrication and experiments, the Cornell group for theory and modeling, and Michelin for testing under realistic conditions and constraints. The project will train graduate students in use-inspired and industry-relevant collaborative research and will provide research opportunities for undergraduate students. The results of this research will be incorporated in an ongoing collaboration with the Da Vinci Science Center in Allentown, PA, for informal science education. A new exhibit will be designed for the general public on bio-inspired design of surfaces to bring out the immediacy and impact of national investments in research and education. Preliminary work has shown that certain surface architectures, for an appropriately designed set of materials and geometrical parameters, exhibit significant enhancement of sliding friction and maintain static friction enhancement against rough surfaces. For example, a film-terminated ridge-valley design (an anisotropic structure with direction-dependent frictional properties) can strongly enhance sliding friction in a direction orthogonal to the ridges by complex internal deformation mechanisms that dissipate energy. For certain combinations of parameters, sliding friction along the ridges can also be enhanced. Such film-terminated fibrillar structures also results in strong enhancement of static friction that is substantially retained even against rough surfaces. These bio-inspired surface architectures have the potential to be transformative by providing dissipation mechanisms at the micron scale that can be optimized by quantitative design of the architecture.