Critical behaviour in the nonlinear elastic response of hydrogels

TL;DR

This study investigates the critical elastic behavior of hydrogels near the gel point, combining simulations and experiments to reveal signatures of marginal stability and nonlinear responses in these networks.

Contribution

It provides experimental and simulation evidence of critical behavior in hydrogels near the gel point, highlighting two distinct critical regimes related to network stability.

Findings

Identification of critical signatures in mechanical response

Experimental evidence supporting theoretical predictions

Discovery of two distinct critical regimes

Abstract

In this paper we study the elastic response of synthetic hydrogels to an applied shear stress. The hydrogels studied here have previously been shown to mimic the behaviour of biopolymer networks when they are sufficiently far above the gel point. We show that near the gel point they exhibit an elastic response that is consistent with the predicted critical behaviour of networks near or below the isostatic point of marginal stability. This point separates rigid and floppy states, distinguished by the presence or absence of finite linear elastic moduli. Recent theoretical work has also focused on the response of such networks to finite or large deformations, both near and below the isostatic point. Despite this interest, experimental evidence for the existence of criticality in such networks has been lacking. Using computer simulations, we identify critical signatures in the mechanical response of sub-isostatic networks as a function of applied shear stress. We also present experimental evidence consistent with these predictions. Furthermore, our results show the existence of two distinct critical regimes, one of which arises from the nonlinear stretch response of semi-flexible polymers..