Influence of Thin Film Confinement on Surface Plasticity in Polystyrene and Poly(2-vinylpyridine) Homopolymer and Block Copolymer Films

Delamination is used 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, delamination shapes are fit to two model functions and a more precise value for curvature is used in the calculation of surface strain. The analysis presented here shows strain levels in thick films to be comparable to bulk measurements. Monitoring the critical strain leads to several observations: (I) as-cast PS-P2VP has a 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 thin-film confinement.