Kinetic viscoelasticity during early polymer-polymer spinodal dewetting

J Lal,L B Lurio,M Sutton,S B Darling,S Narayanan,D Liang

doi:10.1103/physrevresearch.3.043162

Abstract

The dewetting kinetics of a supported polymer bilayer were measured in situ using coherent grazing-incidence x-ray scattering. X-ray photon correlation spectroscopy 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 ultrathin top dewetting film can be directly observed due to the 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, and the power-law exponent can be linked to nonlinear viscoelastic effects, showing similarity in their stress relief dynamics to aftershock decays.

Highlights

The kinetics of hole opening during dewetting displays a fascinating interplay of viscous and elastic energies
In viscoelastic dewetting, coarsening is driven mainly by the mechanical force in the hole-initiation stage, whereas it is driven by the thermodynamic force in the final stage
In analogy to viscoelastic phase separation, the absence of ideal self-similarity is obvious in the scaled structure factor [Fig. 3(a)]

Summary

Introduction

The kinetics of hole opening during dewetting displays a fascinating interplay of viscous and elastic energies. Measurement of the dewetting velocity of large isolated holes due to nucleation in viscoelastic polymer thin films has already been used to get access to mechanical properties of polymers [1,2,3,4,5,6]. These experiments point out the importance of viscoelasticity, not just viscosity, in understanding the dewetting process in thin polymer films on a solid substrate. In this paper on the early stages of viscoelastic spinodal dewetting, many similarities to bulk phase separation, called viscoelastic phase separation [8,9,10,11], are shown

Methods

Results

Conclusion