Mechanical response of double-network gels with dynamic bonds under multi-cycle deformation

Abstract

Mechanical behavior of double-network (DN) gels with covalent and non-covalent bonds under multi-cycle loading depends strongly on time, strain rate and deformation program. A model is developed for the viscoelastic and viscoplastic responses of a polymer network with permanent and temporary junctions. Viscoelasticity is modeled as breakage and reformation of temporary bonds driven by thermal fluctuations. Viscoplasticity is treated as sliding of permanent junctions with respect to their initial positions in the network. Slippage occurs when a junction becomes unbalanced due to transition of a chain linked by this junction from its active state into the dangling state. Analysis of observations in tensile tests with various strain rates, relaxation tests, loading-unloading tests, and multi-cycle tests with various deformation programs on a series of DN gels shows that the experimental stress-strain diagrams are described correctly by the governing equations, material parameters evolve consistently with experimental conditions, and predictions of the model are in quantitative (where sufficient data are provided) and qualitative agreement with experimental data. In particular, numerical simulation demonstrates the ability of the model to describe the Mullins effect in DN gels.

Self‐recovery and fatigue of double‐network gels with permanent and reversible bonds

“…The difference between eqs 1–8 and the governing equations in viscoelastoplasticity of DN gels proposed in our previous studies consists in the following: (a) unlike, the transient network is presumed to be inhomogeneous and composed of meso‐regions with various activation energies for breakage of temporary bonds, (b) contrary to, the strain energy density of the permanent network is adopted in the neo‐Hookean form, and the only mechanism of plastic flow (due to inter‐chain interaction) is taken into account. These simplifications allow eqs 1 and 6 to be presented in the novel form convenient for numerical simulation, and an explicit expression to be derived for elongation ratio under self‐recovery, see eq , which serves as one of the main results of this work.…”