Wiertlewski Michaël, Fenton Friesen Rebecca, Colgate J Edward
Department of Mechanical Engineering, Northwestern University, Evanston, IL 60208; Aix Marseille University, CNRS, Institute of Movement Sciences, F-13009 Marseille, France
Department of Mechanical Engineering, Northwestern University, Evanston, IL 60208;
Proc Natl Acad Sci U S A. 2016 Aug 16;113(33):9210-5. doi: 10.1073/pnas.1603908113. Epub 2016 Aug 1.
When touched, a glass plate excited with ultrasonic transverse waves feels notably more slippery than it does at rest. To study this phenomenon, we use frustrated total internal reflection to image the asperities of the skin that are in intimate contact with a glass plate. We observed that the load at the interface is shared between the elastic compression of the asperities of the skin and a squeeze film of air. Stroboscopic investigation reveals that the time evolution of the interfacial gap is partially out of phase with the plate vibration. Taken together, these results suggest that the skin bounces against the vibrating plate but that the bounces are cushioned by a squeeze film of air that does not have time to escape the interfacial separation. This behavior results in dynamic levitation, in which the average number of asperities in intimate contact is reduced, thereby reducing friction. This improved understanding of the physics of friction reduction provides key guidelines for designing interfaces that can dynamically modulate friction with soft materials and biological tissues, such as human fingertips.
当受到触摸时，被超声横波激发的玻璃板比静止时明显感觉更滑。为了研究这一现象，我们使用受抑全内反射对与玻璃板紧密接触的皮肤表面粗糙度进行成像。我们观察到，界面处的负载由皮肤表面粗糙度的弹性压缩和一层空气挤压膜共同承担。频闪调查显示，界面间隙的时间演化与板的振动部分不同相。综合这些结果表明，皮肤会反弹撞击振动的板，但这种反弹会被一层没有时间从界面分离中逸出的空气挤压膜缓冲。这种行为导致动态悬浮，其中紧密接触的表面粗糙度的平均数量减少，从而降低了摩擦力。对减少摩擦物理原理的这种深入理解为设计能够与软材料和生物组织（如人类指尖）动态调节摩擦力的界面提供了关键指导。
