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Entrainment of particles during the withdrawal of a fiber from a dilute suspension

A fiber withdrawn from a bath of a dilute particulate suspension exhibits different coating regimes depending on the physical properties of the fluid, the withdrawal speed, the particle sizes, and the radius of the fiber. Our experiments indicate that only the liquid without particles is entrained for thin coating films. Beyond a threshold capillary number, the fiber is coated by a liquid film with entrained particles. We systematically characterize the role of the capillary number, the particle size, and the fiber radius on the threshold speed for particle entrainment. We discuss the boundary between these two regimes and show that the thickness of the liquid film at the stagnation point controls the entrainment process. The radius of the fiber provides a new degree of control in capillary filtering, allowing greater control over the size of the particles entrained in the film.