Non-equilibrium behavior of thin polymer films
Katherine R. Thomas, Alexis Chenneviere, Günter Reiter and Ullrich Steiner. Phys. Rev. E 83, 021804 (2011)
Abstract
The rheological behavior of 100nm thick polystyrene lms cast from various solvents was examined using an electric eld to weakly perturb the free surface of the polymer melt. The e ective viscosity and residual stresses of the as-spun lms are seen to strongly depend on the properties of the casting solvent and the solvent quality. Both e ects are explained in terms of the coil dimension at the solvent-polymer composition at which the lm vitri es. The more compact chains in a near-theta-solvent are less entangled and less deformed when quenched to the dry melt compared to the more swollen chains in an athermal solution. Despite chain conformations that are further from equilibrium for the theta-solvent cast chains, these lms have reduced stored stresses compared to the chains cast in lms from athermal solvents. A more detailed analysis of the data suggests that the formation of a surface-near region with more strongly deformed chains during spin-coating. Since thermal equilibration of spin-cast high molecular weight lms is unpractical, solvent vapor annealing was used to equilibrate lms on timescale of a few hours.