Role of Chain Walking and Hopping on Anomalous Self-Diffusion in Linear Associative Polymers

Associative polymers have been shown to exhibit apparent superdiffusion on mesoscopic length scales, attributed to transitions between diffusive modes such as chain walking, hopping, and cluster motion. Here, the effect of sticker density on walking and hopping dynamics in linear associative polymers is probed via Brownian dynamics simulations and forced Rayleigh scattering (FRS) across a wide range of length and time scales. Unexpectedly, the FRS results show superdiffusive scaling for all sticker densities probed, suggesting an ability to hop even for chains with up to 15 stickers. Simulations reveal that hopping can occur in chains with high sticker density due to their enhanced propensity to form loops, which partially counteracts the effect of the additional stickers and increases the likelihood for complete dissociation from the network. The simulations also show that, surprisingly, superdiffusive scaling can arise from walking alone, which is attributed to an increase in strand fluctuations upon unbinding of a sticker compared to shorter timescales when caging restricts motion. Scaling arguments are developed to predict the characteristic walking and hopping diffusivities, finding good agreement with simulation.