Bending of Soft Micropatterns in Elastohydrodynamic Lubrication Tribology

• Published in: Experimental mechanics 2021-07, Vol.61 (6), p.969-979
• Main Authors: Peng, Y., Serfass, C. M., Hill, C. N., Hsiao, L. C.
• Format: Article
• Language: English
• Subjects: Alginates; Aspect ratio; Automation; Bending; Biomechanics; Biomedical Engineering and Bioengineering; Characterization and Evaluation of Materials; Control; Dynamical Systems; Elastohydrodynamic lubrication; Elastomers; Engineering; Film thickness; Flat surfaces; Friction; Hydrogels; Lasers; Lubrication; Manufacturing engineering; Micropatterning; Optical Devices; Optics; Photonics; Photoresists; Polydimethylsiloxane; Research Paper; Robotics; Silicon substrates; Solid Mechanics; Special Issue on Tribology of Advanced Materials; Tribology; Vibration
• ISSN: 0014-4851; 1741-2765
• DOI: 10.1007/s11340-021-00715-8

Background Soft tribology is increasingly important in the design and engineering of materials used in robotics, haptics, and biomechanics studies. When patterned surfaces are part of a lubricated tribopair that undergoes sliding and compressive deformation, the patterns experience a bending strain that affects the lubrication film thickness and elastohydrodynamic friction. The contribution of bending patterns to soft tribology is not well understood because earlier studies focused on hard tribopairs with effectively flat surfaces. Objective We investigate and model the differences in lubricated friction for poly(dimethyl siloxane) (PDMS) elastomer and PEGDA/alginate double network hydrogel patterns in order to determine the effect of height-to-width aspect ratio and bending angle on the elastohydrodynamic friction. Methods Photoresists of two different viscosities are spin coated onto silicon substrates to fabricate molds with pattern heights ranging from 20 μm to 50 μm. Results Tribological characterization of the tribopairs in the elastohydrodynamic lubrication regime shows that the patterns generate a friction peak that is independent of aspect ratio for short patterns but displays a “power-law fit” decrease with increasing aspect ratio for taller patterns. Two independent models are used to estimate the theoretical bending and deflection angles for the tribopairs. Conclusions The decrease in lubricated friction is attributed to taller patterns having large bending angles and a reduced effective surface for fluid load bearing. Results suggest that the bending of micropatterns could be harnessed to engineer lubricated friction in a variety of applications.