Flexible scraping of viscous fluids

Abstract We study the thickness h_d of the liquid film left on a wet surface after scraping it with an elastic wiper (length L, rigidity B) moved at a velocity V. The scraper is clamped vertically at a given distance above the substrate, and h_d is maximal when the tip of the scraper is just tangent to the surface. We show experimentally and theoretically that this maximum thickness is h_max≃ 0.33L η VL²/B) ^3/4 , where η is the liquid viscosity. The deposition law is found to be sensitive to the shape of the wiper: the film thickness can also be tuned by using wipers with a permanent curvature, and varying this curvature.