Suppression of Instability in Polymeric Films Under A Liquid Water-Organic Mixture by Altering the Substrate Wettability

A thin polymer film exposed to a poor solvent can be an effective means of destabilizing an otherwise stable film (in air) by destabilizing polar interactions. Here we investigated instability mediated rupture of stable polystyrene film in a water-organic solution at room temperature. We showed that this instability depends mainly on the Diffusion Length (L) and Spreading Coefficient (S) of the liquid. We observed that for a film of thickness h_E < L, dewetting occurs due to rapid diffusion and spreading of solvent at the substrate-polymer interface whereas for thicker films (h_E > L) wrinkles were observed. Dewetting under such a liquid mix allows penetration of different solvents, based on their respective Permeability (P_S), towards the substrate which causes the adhered polymer chains to loosen up decreasing the viscous friction at polymer-substrate interface leading to a faster dewetting dynamics. We observed that on a solvo-phobic substrate the polymer chains remain adhered to substrate while exposed to the solvent mixture, due to which the film was partially stabilized. Generally, on a phobic substrate a film is unstable in air but while exposed to an effectively poor solvent it is more stable compared to a film on a phillic substrate.