Crazing in Glassy Block Copolymer Thin Films

Abstract

We investigate the crazing process (craze initiation, growth, and failure) in symmetric polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) glassy thin films. PS-b-P2VP is a model material for this study due to its ability to self-assemble into well-aligned lamellar microdomains and the similar mechanical properties for each block (glass transition temperature, crazing stress, entanglement molecular weight, and elastic modulus). These attributes allow us to focus on two primary effects: the effect of an ordered microstructure and the effect of surface terraces on the crazing process in thin glassy polymer films. We find that an ordered lamellar microstructure leads to a higher ratio of craze depth to film thickness in the micronecking process and a lower craze growth rate compared with polystyrene homopolymer. Additionally, surface terracing, or nanoscale steps in the surface topography, impedes craze initiation and significantly decreases the failure strain compared with polystyrene and PS-b-P2VP thin films without surface terraces. These results demonstrate the importance of nanoscale morphologies on the crazing process and point to new directions for understanding the fundamental mechanisms for crazing in advanced materials.