title: Individual Role of the Physicochemical Characteristics of Nanopatterns on Tribological Surfaces.
abstract: Nanoscale patterns have dimensions that are comparable to the length scales affected by intermolecular and surface forces. In this study, we systematically investigated the individual roles of curvature, surface energy, lateral stiffness, material, and pattern density in the adhesion and friction of nanopatterns. We fabricated cylindrical and mushroom-shaped polymer pattern geometries containing flat- and round-topped morphologies using capillary force lithography and nanodrawing techniques. We showed that the curvature, surface energy, and density of the patterns predominantly influenced the adhesive interactions, whereas lateral stiffness dominated friction by controlling the geometrical interaction between the indenter and pillar during sliding. Interestingly, in contrast to previous studies, cylindrical and mushroom-shaped pillars showed similar adhesion characteristics but very different frictional properties. Using fracture mechanics analysis, we showed that this phenomenon is due to a larger ratio of the mushroom flange thickness (t) to the radius of the pillar stem (ρ), and we proposed a design criterion for mushroom patterns to exhibit a geckolike effect. The most important result of our work is the discovery of a linear master curve in the graph of adhesion versus friction for pillars with similar lateral stiffness values that is independent of curvature, material, surface energy, and pattern density. These results will aid in the identification of simple pattern parameters that can be scaled to tune adhesion and friction and will help broaden the understanding of nanoscale topographical interactions.
authors.affiliation: Center for BioMicrosystems, Korea Institute of Science and Technology (KIST) , Seoul 02792, Republic of Korea.
authors.forename: Prashant
authors.initials: P
authors.lastname: Pendyala
authors.affiliation: Department of Mechanical Engineering, School of Engineering, Shiv Nadar University , Uttar Pradesh 201314, India.
authors.forename: Harpreet S
authors.initials: HS
authors.lastname: Grewal
authors.affiliation: Center for BioMicrosystems, Korea Institute of Science and Technology (KIST) , Seoul 02792, Republic of Korea.
authors.forename: Hong Nam
authors.initials: HN
authors.lastname: Kim
authors.affiliation: Center for BioMicrosystems, Korea Institute of Science and Technology (KIST) , Seoul 02792, Republic of Korea.
authors.forename: Il-Joo
authors.initials: IJ
authors.lastname: Cho
authors.affiliation: Center for BioMicrosystems, Korea Institute of Science and Technology (KIST) , Seoul 02792, Republic of Korea.
authors.forename: Eui-Sung
authors.initials: ES
authors.lastname: Yoon
keywords: adhesion; friction; nanopatterns; nanopillar geometry; surface energy