Nanoscale buckling deformation in layered copolymer materials

TL;DR

This study uses molecular simulations to reveal that nanoscale buckling in layered copolymer materials results from kinetic effects rather than microstructural defects, with the undulation wavelength depending on strain rate.

Contribution

It demonstrates that nanoscale buckling wavelength is controlled by strain rate and kinetic effects, challenging the assumption that defects determine undulation size.

Findings

Buckling occurs at the nanoscale with a strain-rate-dependent wavelength.

The undulation wavelength is governed by kinetic effects, not microstructural defects.

Simulations show the buckling mechanism in triblock copolymers under tensile stress.

Abstract

In layered materials, a common mode of deformation involves buckling of the layers under tensile deformation in the direction perpendicular to the layers. The instability mechanism, which operates in elastic materials from geological to nanometer scales, involves the elastic contrast between different layers. In a regular stacking of "hard" and "soft" layers, the tensile stress is first accommodated by a large deformation of the soft layers. The inhibited Poisson contraction results in a compressive stress in the direction transverse to the tensile deformation axis. The hard layers sustain this transverse compression until buckling takes place and results in an undulated structure. Using molecular simulations, we demonstrate this scenario for a material made of triblock copolymers. The buckling deformation is observed to take place at the nanoscale, at a wavelength that depends on strain rate. In contrast to what is commonly assumed, the wavelength of the undulation is not determined by defects in the microstructure. Rather, it results from kinetic effects, with a competition between the rate of strain and the growth rate of the instability. http://www.pnas.org/content/early/2011/12/23/1111367109.abstract