Crosslinked networks of stiff filaments exhibit negative normal stress

TL;DR

This paper presents a computational model demonstrating that stiff biopolymer gels develop negative normal stresses under large strains, linked to filament buckling and nonlinear elastic behavior.

Contribution

The study introduces a novel computational approach connecting negative normal stresses in stiff polymer networks to filament buckling and nonlinear elasticity.

Findings

Networks develop negative normal stresses comparable to shear stress.

Negative normal stresses are associated with filament buckling.

Negative normal stresses are characteristic of nonlinear elastic stiff gels.

Abstract

Motivated by recent experiments showing that stiff biopolymer gels exhibit highly unusual negative normal elastic stresses, we develop a computational model for stiff polymer networks subject to large strains. In all cases, we find that such networks develop normal stresses that are both negative and of magnitude comparable to the corresponding shear stress. We find that these normal stresses coincide with other nonlinearities in our networks, and specifically with compressive bucking of the individual filaments. Our results suggest that negative normal stresses are a characteristic feature of stiff (bio)polymer gels that have been shown to exhibit strong nonlinear elastic properties.