Self-Diffusion of Associating Star-Shaped Polymers

Abstract

The dynamics of associating bonds in transient polymer networks exerts a paramount influence on their relaxation and timedependent mechanical properties. In particular, diffusive motion of polymers mediated by the dissociation and association equilibrium of reversible junctions can affect the materials' structural stability, dynamic mechanical properties, and a broad spectrum of functionality that arises from the constant motion of polymer chains. In this work, forced Rayleigh scattering is used to measure the diffusion of terpyridine end-functionalized four-arm poly(ethylene glycol) polymers transiently interlinked by zinc ions in organic solvent across a wide range of length and time scales. Phenomenological superdiffusion, where the scaling of the squared length dimension vs time has a power-law exponent larger than one, is demonstrated as an intrinsic feature of these networks due to the interplay of chain dissociation and diffusion. Outside the superdiffusive regime, normal Fickian diffusion is recovered on both large and small length scales. The data are quantitatively described with a previously developed two-state model of one fast and one slow diffusing species that are allowed to interconvert. The extracted diffusivities show concentration-dependent scaling in good agreement with the sticky Rouse model. Diffusion of the same polymers but with only three associating arms through the same transient networks is also investigated, which exhibits faster chain diffusivities compared to the case of the polymers with four associating arms. These experimental results quantitatively show the effect of sticker density and valency on chain diffusion in transient polymer networks.

Dynamic Model Metallo‐Supramolecular Dual‐Network Hydrogels with Independently Tunable Network Crosslinks

“…In contrast to the permanent structure of covalent networks, be it inhomogeneous or model type, the reversibility of physical network junctions causes the structure of physical networks to evolve through time; it is also an inherent cause for relaxation of these materials upon external load. The dynamics of opening and closing of physical network junctions inherently determines how fast such relaxation or restructuring occurs.…”

Connectivity Defects and Collective Assemblies in Model Metallo‐Supramolecular Dual‐Network Hydrogels

“…In contrast to such permanent chemical networks, purely physically crosslinked networks have a structure that evolves through time . In this context, the dynamics of the reversible bonds determines the rate of structural development in response to external stimuli.…”

Emergence, evidence, and effect of junction clustering in supramolecular polymer materials

“…163,176 On the microscale, parameters such as the translational polymer-chain diffusion coefficient are measured by microscopy-based techniques like fluorescence recovery after photobleaching (FRAP) or forced Rayleigh scattering (FRS). 177,178 In summary, the macroscopic properties of supramolecular polymer materials are closely tied, not only to the structure and dynamics of the polymer backbone but to that of the supramolecular bonds. However, in dilute conditions, where the entanglement of the polymer precursor is negligible and as such the polymeric dynamics is hardly traceable on experimental timescales, the…”