  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.
