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Flows at soft interfaces : the roles of elasticity, capillarity & fluctuations

Authors
  • Bertin, Vincent
Publication Date
Sep 09, 2021
Source
HAL
Keywords
Language
English
License
Unknown
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Abstract

In this manuscript, we study flows in the vicinity of soft interfaces through various systems. In a first part, we focus on elastohydrodynamic lubrication, and analyze the confined motion of a rigid sphere moving close to a soft surface. The hydrodynamic interactions between an oscillating sphere and the deformation of the surface allow us to characterize without contact the complex mechanical response of materials, such as viscoelasticity, poroelasticity or capillarity. Theoretical results are confronted with colloidal-probe atomic force microscopy experiments, allowing us to measure the rheology of elastomers and the surface tension of liquid-air interfaces in the presence of impurities. Then, we calculate the forces and torques that apply on spheres that are free to move and rotate in all directions. The elastohydrodynamic lift force, measured experimentally, is in agreement with theoretical predictions for small surface deformations. In a second part, we focus on the dynamics of thin films. Through theoretical and experimental work on the capillary leveling of thin polymer films, we analyze the dynamics of films resting on an elastic substrate, bilayer films and freestanding films. A last part is dedicated to the diffusion of spheres in shear flows and near a wall. We analyze the enhancement of the effective diffusion coefficient induced by the coupling between diffusion and advection. Particular interest is given to the dynamics at short times compared with the diffusion time and to the interactions of the particles with the wall.

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