title: Critical behaviour in the nonlinear elastic response of hydrogels.
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.
authors.affiliation: Department of Physics and Astronomy, Vrije Universiteit, 1081-HV Amsterdam, The Netherlands and Department of Applied Physics and Institute for Complex Molecular Systems, Eindhoven University of Technology, 5600-MB Eindhoven, The Netherlands.
authors.forename: M
authors.initials: M
authors.lastname: Dennison
authors.affiliation: Radboud University Nijmegen, Institute for Molecules and Materials, Department of Molecular Materials, 6525-AJ Nijmegen, The Netherlands.
authors.forename: M
authors.initials: M
authors.lastname: Jaspers
authors.affiliation: Radboud University Nijmegen, Institute for Molecules and Materials, Department of Molecular Materials, 6525-AJ Nijmegen, The Netherlands.
authors.forename: P H J
authors.initials: PH
authors.lastname: Kouwer
authors.affiliation: Department of Applied Physics and Institute for Complex Molecular Systems, Eindhoven University of Technology, 5600-MB Eindhoven, The Netherlands.
authors.forename: C
authors.initials: C
authors.lastname: Storm
authors.affiliation: Radboud University Nijmegen, Institute for Molecules and Materials, Department of Molecular Materials, 6525-AJ Nijmegen, The Netherlands.
authors.forename: A E
authors.initials: AE
authors.lastname: Rowan
authors.affiliation: Department of Physics and Astronomy, Vrije Universiteit, 1081-HV Amsterdam, The Netherlands and Departments of Chemical and Biomolecular Engineering, Chemistry and Physics, Rice University, Houston, TX, USA.
authors.forename: F C
authors.initials: FC
authors.lastname: MacKintosh