Molecular transport in dense, crowded media is often affected by binding and collisions with obstacles, leading to complex spatial distributions and anomalous diffusion on multiple length scales. Here, neutron spin-echo (NSE) spectroscopy and forced Rayleigh scattering (FRS) were used in tandem to study the interplay between segmental and center-of-mass chain dynamics in the presence of strong binding interactions in a model protein hydrogel. The results provide evidence for several dynamic scaling regimes of gel relaxation behavior with varying length scale, including a caging regime bridging submolecular relaxation and center-of-mass diffusion due to transient binding. On mesoscopic length scales larger than the size of the cage, chains undergo two distinct regimes of apparent superdiffusive scaling, with different power-law exponents, before the onset of terminal Fickian diffusion. The combined NSE and FRS results are interpreted in the context of prior Brownian dynamics simulations of associating star polymers, revealing insight into structural length scales and binding kinetics governing the transition from segmental relaxation to self-diffusion in the protein hydrogel. Finally, single-sticker tracer diffusion measurements were performed to directly probe sticker association/dissociation dynamics within the gel, the results suggesting that cooperative cluster motion may play a role in network relaxation on larger length scales.

• Received 28 February 2020
• Accepted 30 October 2020

DOI:https://doi.org/10.1103/PhysRevResearch.2.043369

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Published by the American Physical Society