Abstract

The spreading of complex fluids is essential in many industrial processes for example in the cosmetic industry. We study here the spreading of complex fluids in two different geometries: dip coating experiments where a rod is pulled out of a yield stress fluid and soft blade experiments where a coating film is obtained by squeezing a liquid drop with a soft elastic blade. In the dip coating experiment with a yield-stress fluid, we show that the thickness of the coating film does not follow the classical Landau-Levich theory which is based on the drainng of the film. Rather the thickness of the film is limited by the hydrodynamics of the bulk reservoir. We propose scaling laws for the film thickness and discuss the cross over between thes two possible behaviors. In the soft blade experiment we first study simple non-newtonian fluids an show the importance of the wetting length, which measures the ize of the blade a the tip wetted by the fluid. We then generalize our study to shear-thinning and normal stress fluids.