Investigation of surface deformation during drying of thin polymer films due to Marangoni convection

The investigation of surface deformation of thin polymer films (methanol–poly(vinyl acetate) solution with 67 wt.% methanol) due to inhomogeneous drying is presented. Of interest are the onset of fluid instability and the influence of drying kinetics in a system where surface tension depends on temperature and composition. An experimental method is used that correlates a virtual shift of a random dot pattern, located on the downside of a glass substrate, to a deformation of the free surface of a transparent film. Instability in the fluid is forced over a structured composite substrate with inhomogeneous thermal conductivity. We show that due to the inhomogeneous heat transfer a long-wave instability mode is triggered resulting in directed mass transport. To evaluate the driving forces, 1D simulations of the non-isothermal drying process have been performed. Furthermore the influence of drying kinetics on the developing surface topology is discussed.