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

TL;DR

This study investigates how thin film confinement affects the onset of surface plasticity in polystyrene and poly(2-vinylpyridine) homopolymers and block copolymers, revealing that confinement and microstructural ordering influence critical strain levels.

Contribution

It provides a quantitative analysis of the critical strain for plasticity in thin polymer films, linking microstructural state and confinement to surface plasticity behavior.

Findings

Critical strain levels in thick films are comparable to bulk measurements.

Annealing increases critical strain due to microstructural ordering.

Both as-cast and ordered films show increased critical strain under confinement.

Abstract

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.