Viscoelasticity of gels with dynamic bonds: molecular kinetics and macroscopic mechanics

Incorporation of dynamic bonds into the polymer network of soft gels has been exploited as a strategy to enhance fracture toughness and to enable self-healing. Gels with dynamic bonds often exhibit macroscopic viscoelasticity which can be traced back to the kinetics of dynamic bonds undergoing dissociation and reformation. I will present our recent efforts to connect the molecular-level chemical kinetics to the continuum-level viscoelasticity. As a model system, I will focus on a hydrogel with two types of crosslinks: dynamic physical crosslinks and permanent chemical crosslinks, and describe two different approaches for modeling the relation between molecular kinetics and viscoelasticity. These two approaches are shown to capture experimental data of tensile tests with various strain histories and oscillatory torsion tests. I will also discuss how our modeling approach can potentially lead to a general theoretical framework of nonlinear viscoelasticity.