Promoting rotation, friction, and mixed lubrication for particles rolling on microstructured surfaces

Brian K. Ryu, Richard J. Hommel, Paul Roberts, and Joëlle Fréchette
Phys. Rev. E 99, 022802 – Published 20 February 2019
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Abstract

We investigate how the aspect ratio of micropillar or microwell arrays patterned on a surface affects the rolling and slipping motion of spheres under flooded conditions at low Reynolds numbers. We study arrays of rigid microstructures with aspect ratios varying over two orders of magnitude for surface coverages ranging from 0.04 to 0.96. We investigate how the surface features (dimensions, surface coverage, and geometry) individually impact the motion of the sphere. We find that increasing microstructure height results in higher rotational velocities on all studied surfaces. We then model the motion of the spheres using two physical parameters: an effective separation and a coefficient of friction between the sphere and the incline. We find that a simple superposition of resistance functions, previously shown to accurately predict the motion of spheres for different surface coverages and geometries, indeed shows good agreement with experimental outcomes for all microstructure heights studied. We also perform separate sliding friction measurements via a force microscope to measure the coefficient of friction between the sphere and incline, under identically flooded conditions. A comparison of the sliding friction measurements at different Hersey numbers suggests that the effect of the microstructure on the coefficient of friction becomes more important as the Hersey number increases.

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  • Received 25 August 2018

DOI:https://doi.org/10.1103/PhysRevE.99.022802

©2019 American Physical Society

Physics Subject Headings (PhySH)

Fluid Dynamics

Authors & Affiliations

Brian K. Ryu, Richard J. Hommel, Paul Roberts, and Joëlle Fréchette*

  • Department of Chemical and Biomolecular Engineering, Johns Hopkins University, Baltimore, Maryland 21218, USA

  • *jfrechette@jhu.edu

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Issue

Vol. 99, Iss. 2 — February 2019

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