Issue 25, 2020

Capillary-driven indentation of a microparticle into a soft, oil-coated substrate

Abstract

Small scale contact between a soft, liquid-coated layer and a stiff surface is common in many situations, from synovial fluid on articular cartilage to adhesives in humid environments. Moreover, many model studies on soft adhesive contacts are conducted with soft silicone elastomers, which possess uncrosslinked liquid molecules (i.e. silicone oil) when the modulus is low. We investigate how the thickness of a silicone oil layer on a soft substrate relates to the indentation depth of glass microspheres in contact with crosslinked PDMS, which have a modulus of <10 kPa. The particles indent into the underlying substrate more as a function of decreasing oil layer thickness. This is due to the presence of the liquid layer at the surface that causes capillary forces to pull down on the particle. A simple model that balances the capillary force of the oil layer and the minimal particle–substrate adhesion with the elastic and surface tension forces from the substrate is proposed to predict the particle indentation depth.

Graphical abstract: Capillary-driven indentation of a microparticle into a soft, oil-coated substrate

Supplementary files

Article information

Article type
Paper
Submitted
19 Feb 2020
Accepted
09 May 2020
First published
11 May 2020

Soft Matter, 2020,16, 5812-5818

Author version available

Capillary-driven indentation of a microparticle into a soft, oil-coated substrate

J. D. Glover and J. T. Pham, Soft Matter, 2020, 16, 5812 DOI: 10.1039/D0SM00296H

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