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Coating of complex fluids - Annie Colin

ESPCI Paris - Université PSL

Heure : 9 avr. 2021 11:00 AM Paris
ID de réunion : 838 1828 3502
Code secret : mGP0PV

In order to treat surfaces, thin layers of complex fluids, suspensions are deposited on surfaces. In this talk I will present two experimental geometries for deposition : Dip coating and a elastic blade. I will study both simple and complex fluids. The dip-coating process consists of withdrawing immersed objects from a liquid reservoir. After withdrawal, a significant layer of liquid remains on the object. Various industrial processes (food and beverage industry, automotive industry) use this technique to coat or treat surfaces. Recent studies have shown that the thickness of deposit is determined by the flow inside the reservoir for yield-stress fluids. This is different from the behavior of simple liquids for which the coating thickness is solely determined by the flow inside the meniscus. In this work, we re-examine this question and propose a complete phase diagram linking the Newtonian case and the yield-stress fluid case. We provide asymptotic scaling laws for extreme cases. A good agreement with experiments is obtained. The spreading of fluid by a deformable blade is also a common industrial problem, characteristic of elasto-hydrodynamic situations. Here, I will consider the case of a finite reservoir of liquid, emptying as the liquid is spread. I will evidence the role of a central the wetting length lw, which sets a boundary between the wet and dry parts of the blade. I will show that the deposited film thickness e depends quadratically with lw. We study this problem experimentally and numerically by integration of the elasto-hydrodynamic equations, and finally propose a scaling law model to explain how lw influences the spreading dynamics.This study is performed on Newtonian fluids but also on complex fluids.

References :
Krapez, Marion, Anaïs Gauthier, Hamid Kellay, Jean-Baptiste Boitte,
Odile Aubrun, Jean-François Joanny, and Annie Colin. "Impact of the
Wetting Length on Flexible Blade Spreading." Physical Review Letters
125, no. 25 (2020) : 254506.

Smit, Wilbert J., Christophe Kusina, Jean-François Joanny, and Annie
Colin. "Stress Field inside the Bath Determines Dip Coating with
Yield-Stress Fluids in Cylindrical Geometry." Physical review letters
123, no. 14 (2019) : 148002


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