Composition fluctuation intensity effect on the stability of polymer films

Abstract

The critical fluctuation intensity for the occurrence of dewetting, the basic and key problem in dewetting by means of composition fluctuation, remains obscure. In this work, therefore, the stability and fluctuation intensity of polymer films upon blending a tiny amount of a miscible component was investigated by taking poly(methyl methacrylate)/poly(styrene-ran-acrylonitrile) (i.e. PMMA/SAN) as an example. Our results indicate that both neat PMMA and neat SAN films wet the substrate of silicon oxide thermodynamically. SAN (with 1% or 2% PMMA) films dewet this substrate completely, while PMMA (with tiny amount of SAN) films are stable upon annealing at 145 °C. The fit and extrapolation of the RMS_roughness suggest that the composition fluctuation and consequent surface undulation intensity accounts for the difference in film stability. The higher magnitude of fluctuation intensity results in the dewetting of the SAN film. On the other hand, the stronger interaction between PMMA and silicon oxide depresses the fluctuation and surface undulation along the film, which is the reason for the stable PMMA film.