Morphological features and dewetting behaviour of thin polymer films coated on porous substrates

Polymer thin films coated onto non-wetting substrates tend to become unstable and dewet when heated above the glass transition temperatures. Such dynamics are relevant to applications like organic microelectronics and lithography that require non-continuous and arrayed thin polymer films. In several situations, the substrate of interest has finite permeability due to its porous surface, as in paper, fabric, or sandstones, which may modify the hydrodynamics of a liquid film. In the present work, we report model experiments of thin polystyrene films dewetting nanoporous alumina membranes of different pore sizes. Polystyrene films are prepared by spin coating a toluene-based solution, and heated above the glass transition temperature to initiate dewetting. The effect of annealing time on morphologies of the film is studied. During annealing, the film dewets the porous substrate. However, as pores become saturated, excess polymer self-organizes into a uniform coating. The dynamics of liquid film dewetting near permeable substrates are explained from a fluid mechanical perspective through numerical simulations. (C) 2021 Elsevier Ltd. All rights reserved.