Effects of solvent vapor annealing duration on the dewetting of two kinds of spin-coated bilayer films of polystyrene-block-poly(methyl methacrylate)/poly(styrene-co-acrylonitrile) (PS-b-PMMA/SAN, upper/lower) and SAN/PS-b-PMMA were mainly studied by atomic force microscopy and contact angle measurement technique. In the PS-b-PMMA/SAN bilayer film, the continuous upper film first appears holes and then ruptures into droplets which fuse and break periodically, which is different from the single increase and decrease evolution in the spin-coated PS-b-PMMA monolayer film. The periodic droplet evolution is due to the preferred affinity with acetone to PMMA blocks and the change of the film surface energy. The droplet diameters are smaller than those in our previous PS-b-PMMA monolayer films. This illustrates that the interactions between PS blocks of PS-b-PMMA layer and styrene segments of SAN layer are stronger than those between PMMA blocks of monolayer film and the substrate. In the SAN/PS-b-PMMA bilayer film, on the other hand, the SAN upper layer does not form the continuous film during the spin-coating process and occurs microphase separation due to the surface energy difference of AN and styrene segments and their thermodynamic incompatibility. The dewetting behavior occurs in the bilayer films induced by acetone vapor, and the droplet sizes are not uniform.

Article address: https://link.springer.com/article/10.1007/s10965-022-03354-2

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