Spinodal Surface Fluctuations on Polymer Films

We study the temporal growth pattern of surface fluctuations on a series of spinodally unstable polymer films where the degree of instability is controlled by the film thickness. For films in the deep spinodal region, the growth rate function of the surface modes as a function of the wavevector,, fits well to the mean-field theory. As the film thickness is increased and the film instability decreases, the mean-field theory demonstrates marked disagreement with experiment, notwithstanding provision of the known corrections for random thermal noise. We show that the deviations arise from large-amplitude fluctuations induced by homogeneous nucleation, which has not been considered in conventional treatment of thermal noise.