Dip-coating of suspensions

Abstract

Withdrawing a plate from a suspension leads to the entrainment of a coating layer of fluid and particles on the solid surface. In this article, we study the Landau-Levich problem in the case of a suspension of non-Brownian particles at moderate volume fraction $10\%<\varphi <41\%$. We observe different regimes depending on the withdrawal velocity $U$, the volume fraction of the suspension $\varphi$, and the diameter of the particles $2a$. Our results exhibit three coating regimes. (i) At small enough capillary number $Ca$, no particles are entrained, and only a liquid film coats the plate. (ii) At large capillary number, we observe that the thickness of the entrained film of suspension is captured by the Landau-Levich law using the effective viscosity of the suspension $\eta (\varphi )$. (iii) At intermediate capillary numbers, the situation becomes more complicated with a heterogeneous coating on the substrate. We rationalize our experimental findings by providing the domain of existence of these three regimes as a function of the fluid and particles properties.

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• Landau-Levich Enhanced Cheerios Effect
• Entrainment of particles during the withdrawal of a fiber from a dilute suspension
• Droplet detachment and pinch-off of bidisperse particulate suspensions