Time Evolution Study on the Spinodal Dewetting of Polymer Films

Liquid films deposited on non-wettable substrate surfaces are unstable and may rupture spontaneously into liquid droplets. It has been suggested that the initial rupturing process is similar to that of spinodal decomposition. We used atomic force microscopy to investigate the time evolution of the spinodal dewetting of polystyrene (PS) thin films on oxide- coated silicon, which enables us to measure $\Gamma (\lambda )$, the spectroscopic initial rupturing rate of the films. We found that $\Gamma (\lambda )$ demonstrates a peak at a wavelength, $\lambda _{max}$, and falls to zero either when $\lambda $ increases towards $\infty$ or decreases towards $\surd $2/2 $\lambda _{max}$. The data indeed fit well to $\Gamma (\lambda ) =\Gamma (\lambda _{\max } )(2\lambda ^{-2}_{max}\lambda ^{-2} -\lambda ^{-4})\lambda _{\max }^4 $, expected from the result of Cahn for the spinodal decomposition rate of phase separating binary mixtures.