Kinetic viscoelasticity during early polymer-polymer spinodal dewetting*

 The dewetting kinetics of a supported polymer bilayer were measured in-situ using coherent

grazing incidence x-ray scattering. X-ray photon correlation spectroscopy (XPCS) provides both

the two-time correlation functions and the cross-correlation function which measures the average

spatial shift of the speckles produced by the coherent x-rays. The stress in the ultra-thin dewetting top film can be directly observed due to exquisite sensitivity to sample curvature changes provided by the x-ray speckle correlation functions. The hole opening events in the film are found to be associated with significant changes to the stress. These results are interpreted through an analogy between viscoelastic spinodal dewetting and early-stage bulk viscoelastic phase separation. The frequency of hole initiation events during dewetting decreases with time as a power law, the power-law exponent can be linked to non-linear viscoelastic effects; showing similarity in their stress relief dynamics to aftershock decays.