Frictional sliding between patterned surfaces is of fundamental and practical importance in the haptic engineering of soft materials. In emerging applications such as remote surgery and soft robotics, thin fluid films between solid surfaces lead to a multiphysics coupling between solid deformation and fluid dissipation. Here, we report a scaling law that governs the peak friction values of elastohydrodynamic lubrication on patterned surfaces. These peaks, absent in smooth tribopairs, arise due to a separation of length scales in the lubricant flow. The framework is generated by varying the geometry, elasticity and fluid properties of soft tribopairs and measuring the lubricated friction with a triborheometer. The model correctly predicts the elastohydrodynamic lubrication friction of a bioinspired robotic fingertip and human fingers. Its broad applicability can inform the future design of robotic hands or grippers in realistic conditions, and open up new ways of encoding friction into haptic signals.
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The authors thank R. Ewoldt, J. F. Brady, R. G. Larson, J. Frechette and A. Dunn for discussions. Y.P., C.M.S., C.N.H. and L.C.H. were supported in part by the National Science Foundation (NSF) through award no. CBET-2042635 and the AAAS Marion Milligan Mason Award. K.G. was funded by the Eugene V. Cota-Robles Fellowship from the University of California, Los Angeles. Y.V. was supported by the NSF through award no. 1751348.
The authors declare no competing interests.
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Peng, Y., Serfass, C.M., Kawazoe, A. et al. Elastohydrodynamic friction of robotic and human fingers on soft micropatterned substrates. Nat. Mater. 20, 1707–1711 (2021). https://doi.org/10.1038/s41563-021-00990-9
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