A polymer film exposed to a liquid solvent mixture can be an effective means of destabilizing an otherwise stable film (in air). Here we investigated the mechanism of dissolution induced instability and rupture of stable polystyrene (PS) films under a liquid Water organic mixture at room temperature. It is different from other dewetting techniques such as solvent vapor annealing, thermal annealing etc. This type of dewetting is a two-stage process where initially all the components of the liquid bath diffuse into the film via a non-Fickian diffusion mechanism by swelling induced chain relaxation. At the first stage, the good solvent dissolves the more swelled regions of the film and ultimately the initial holes are formed. We also observed sluggish dewetting dynamics and low no density of holes for thicker PS films. At the second stage, the solvent spreads on the substrate and preferentially gets adsorbed on it, allowing retraction of the rim of the initial holes which eventually leads to formation of bi-continuous threads and droplets. We showed that first stage depends on the Diffusion Length (<b><i>L</i></b>) of the good solvent whereas the later stage is highly influenced by substrate wettability. We altered the substrate wettability and suppressed this later stage solvent spreading as well as further dewetting. Presence of poor and non-solvents greatly reduces the glass transition temperature of the film although they cannot induce dewetting by themselves.

Mechanism of dissolution induced dewetting of stable polymer films under liquid water organic mixture: Role of diffusion length and substrate wettability

256th National Meeting (2018)

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