The Influence of Thin Film Confinement on Surface Plasticity in   Polystyrene and Poly(2-vinylpyridine) Homopolymer and Block Copolymer Films
  Thin block copolymer films have attracted considerable academic attention because of their ability to self-assemble into various microstructures, many of which have potential technological applications. Despite the ongoing interest, little effort has focused on the onset of plasticity and failure which are important factors for the eventual adoption of these materials. Here we use delamination to impart a quantifiable local stain on thin films of homopolymer polystyrene and poly(2-vinylpyridine), as well as block copolymers made of styrene and 2-vinylpyridine. Direct observation of the damage caused by bending with atomic force microscopy and laser scanning confocal microscopy, leads to the identification of a critical strain for the onset of plasticity. Moving beyond our initial scaling analysis, the more quantitative analysis presented here shows strain levels for thick films to be comparable to bulk measurements. Monitoring the critical strain leads to several observations: 1.) as-cast PS-P2VP has low critical strain, 2.) annealing slowly increases critical strain as microstructural ordering takes place, and 3.) similar to the homopolymer, both as cast and ordered films both show increasing critical strain under confinement. 
Bekele J. Gurmessa and Andrew B. Croll
cond-mat.soft