A network model of transient polymers: exploring the micromechanics of nonlinear viscoelasticity

Abstract

Dynamic networks contain crosslinks that re-associate after disconnecting, imparting them with viscoelastic properties. While continuum approaches have been developed to analyze their mechanical response, these approaches can only describe their...

Thermosensitive P(AAc‐co‐NIPAm) Hydrogels Display Enhanced Toughness and Self‐Healing via Ion–Ligand Interactions

“…Continuum Model: Statistical Mechanics Approach: To inversely deduce the microstructural features of the hydrogels as their concentration of Fe 3+ and compositional monomer ratios are varied, the Transient Network Theory (TNT) (developed for polymeric materials containing some combination of permanent and reversibly bonded crosslinks) is adapted. [39,40] This statistical approach envisions P(AAc-co-NIPAm) hydrogels as a percolated network [45] of flexible, polymeric chains comprised of the copolymers, which introduces some long-term elastic stress response, 𝝈 e . Interstitially along the lengths of these chains, Fe 3+ coordinates with functional groups to create reversible crosslinks whose dissociation unveils hidden lengths of polymer chains causing energy dissipation and introducing some ratedependent component of stress response, 𝝈 d .…”

“…This suggested slip bond behavior is commonplace [44] and supported by the results of Figure 2F which also displays an inverse relation between k d and stress magnitude. [45,46] To further explore the dissipative effects of reversible bond dissociation, we also evaluated the mechanical response of D h-0.033-Y hydrogels undergoing cyclic uniaxial loading experiments with no recover time between cycles. Figure 5A shows the engineering stress-strain response of a D h-0.033-2 hydrogel undergoing cyclic loading to different peak strains.…”

Coupled bond dynamics alters relaxation in polymers with multiple intrinsic dissociation rates

“…The network model used here, introduced by Wagner et al (2021), 29 simulates discrete networks within 2D, periodic, representative volume elements to which deformations may be applied. For detailed methods pertaining to network initiation and spatiotemporal normalization, see ESI † Section SIA.…”

“…Either stable or dynamic telechelic bonds may form between neighboring nodes, the latter of which are assigned some constant dissociation kinetic rate, k d . Bond association is captured through the sub-diffusive Rouse scaling utilized in Wagner et al (2021), 29 that gives the attachment rate as: 33…”

“…To address this limitation, many researchers have resorted to network-scale modeling to explore polymeric microstructure. 3,[26][27][28][29][30][31] We here employ one such recently developed model 29 to investigate the percolation threshold of stable bonds in 2D networks containing interstitial dynamic bonds (Fig. 1).…”