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

橡胶材料与坚硬表面的摩擦在许多应用中具有重要的实际意义。例如，它决定轮胎、挡风玻璃刮水器和密封件的性能和效率。以前关于控制其摩擦机制的许多工作要么改变了橡胶的表面化学成分，要么改变了橡胶本身的性质。最近对生物附着装置的研究表明，橡胶的近表面结构设计也可以显著提高橡胶的附着力，但通常情况下，橡胶的滑动摩擦会减少而不是增加。GOALI项目的主要目标是研究表面结构，以增强与粗糙和光滑表面的滑动和静摩擦。目标应用是改善轮胎的摩擦力，计划中的研究需要在现实约束和条件下进行设计和理论、制造和测试方面的工作。出于这个原因，该项目是两个大学实验室(康奈尔和利哈伊)和米其林北美的一名工业研究员合作的。利哈伊小组负责制造和实验，康奈尔小组负责理论和建模，米其林小组负责在现实条件和约束下进行测试。该项目将培训研究生在应用启发和与行业相关的合作研究方面，并将为本科生提供研究机会。这项研究的结果将被纳入正在进行的与宾夕法尼亚州阿伦顿的达芬奇科学中心的合作，用于非正式的科学教育。将为公众设计一个新的展览，介绍表面的生物灵感设计，以展示国家对研究和教育投资的即时性和影响力。初步工作表明，对于适当设计的一组材料和几何参数，某些表面结构表现出显著的滑动摩擦增强，并保持对粗糙表面的静态摩擦增强。例如，薄膜终止的脊谷设计(一种具有方向相关摩擦特性的各向异性结构)可以通过复杂的内部变形机制来耗散能量，从而大大增强垂直于山脊的方向上的滑动摩擦。对于某些参数组合，还可以增强沿山脊的滑动摩擦力。这种薄膜端接的纤维结构还导致即使在粗糙表面上也基本保持的静摩擦的显著增强。这些受生物启发的表面建筑具有潜在的变革性，它提供了微米级的耗散机制，可以通过建筑的定量设计来优化。

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.