Effects of withdrawal velocity and rheological properties on film thickness of dip coating film of polymer solutions

Abstract

Dip coating flows of polymer solutions were experimentally studied. A plate was coated with a solution at several withdrawal velocities. The effects of both the withdrawal velocity and rheological properties of polymer solutions on the film thickness were investigated. The film thickness was measured with a CCD laser displacement sensor. In addition, shape of the film surface in a meniscus region was observed. Five fluids were used as test fluids: two Newtonian fluids having different viscosities and three polymeric liquids which have almost the same shear viscosity and are different in elasticity. For every test fluid, the film thickness increased with increasing the withdrawal velocity. The increasing rate of the film thickness was almost constant for Newtonian fluids, while it decreased with increasing the withdrawal velocity for polymer solutions with shear-thinning viscosity. Moreover, the comparison of the results for the three polymer solutions showed that the film became thin for a polymer solution with high elasticity.