465413 Elastic Deformation of Soft Supported Films of Finite Thickness during the Drainage of a Viscous Fluid

Wednesday, November 16, 2016: 9:00 AM
Powell I (Parc 55 San Francisco)
Joelle Frechette and Yumo Wang, Chemical and Biomolecular Engineering, Johns Hopkins University, Baltimore, MD

Elastic deformation of soft supported films of finite thickness during the drainage of a viscous fluid

Joelle Frechette and Yumo Wang, Chemical and Biomolecular Engineering, Johns Hopkins University, Baltimore MD 21218

Elastohydrodynamic deformation can cause lift and reduce friction during sliding and alter the rheological properties of soft colloidal particles. It also modifies the shape of approaching surfaces, a determining factor for the adhesion dynamics to wet or flooded surfaces. When studying elastohydrodynamics in soft matter it is a challenge to measure simultaneously the hydrodynamic forces and the deformation, both necessary to understand how contact is reached and the coupling between deformation of the solid and viscous dissipation in the fluid.

In this presentation the characterization of the spatiotemporal deformation of an elastic film during the radial drainage of fluid from a narrowing gap will be discussed. As predicted, we will show that the elastic deformation of a thick film takes the form of a dimple and prevents full contact to be reached.1 We reveal the importance of measuring absolute surface separation when working with soft materials by showing the effects of viscoelasticity of the solid in the fluid film profiles, and point out that elastic compliance leads to lower hydrodynamic forces at a given time while deformation leads to stronger forces at a given fluid film thickness.With thin supported elastic films the stress caused by fluid drainage becomes increasingly transferred to the underlying rigid substrate and the dimple formation is suppressed, which allows the surfaces to reach full contact (See top of Figure 1). For intermediate film thicknesses we observe shapes that are more complex when close to contact (see bottom of Figure 1). These shapes originate from lubrication pressure and its corresponding deformation distribution on a curved, layered compliant system. We extend existing models for elastohydrodynamic deformation to the more general case of the compliant material being part of a multi-layer system instead of a half-space. When taking the finite thickness of the compliant film into account we predict the same complex morphology as the ones observed in experiments. Our work is the first reported and validated prediction that such complex surface profiles exist in elastic solid and we draw analogies to the cases of “wimple” or “pimple” that have been observed in droplets.

FIG. 1. (Left) Schematic of the elastohydrodynamic problem highlighted on effects of film thickness. Grey core: rigid substrate; Red layer: compliant coating. Up: thin film; down: intermediate thickness film. (Right) experimental deformation profile of the compliant coatings caused by lubrication forces with corresponding film thicknesses.

 Reference:

1. Wang, Y., C. Dhong, and J. Frechette, Out-of-Contact Elastohydrodynamic Deformation due to Lubrication Forces. Physical review letters, 2015. 115(24): p. 248302.


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