Stability and Elasticity of Ultrathin Sphere-Patterned Block Copolymer Films

TL;DR

This study uses self-consistent field theory to analyze the elastic properties of ultrathin sphere-patterned block copolymer films, revealing their stability characteristics and elastic moduli relationships.

Contribution

It provides the first theoretical investigation of the elastic response and stability of sphere-patterned ultrathin block copolymer films.

Findings

In-plane elastic moduli follow hexagonal symmetry expectations.

Pure shear and simple shear moduli differ by about 20%.

Bending constants are negative, indicating inherent instability.

Abstract

Sphere-patterned ultrathin block copolymers films are potentially interesting for a variety of applications in nanotechnology. We use self-consistent field theory to investigate the elastic response of sphere monolayer films with respect to in-plane shear, in-plane extension and compression deformations, and with respect to bending. The relations between the in-plane elastic moduli is roughly compatible with the expectations for two-dimensional elastic systems with hexagonal symmetry, with one notable exception: The pure shear and the simple shear moduli differ from each other by roughly 20%. Even more importantly, the bending constants are found to be negative, indicating that free-standing block copolymer membranes made of only sphere mono-layer are inherently unstable above the glass transition. Our results are discussed in view of experimental findings.