Gels made of telechelic polymers connected by reversible crosslinkers are a
versatile design platform for biocompatible viscoelastic materials. Their
linear response to a step strain displays a fast, near-exponential relaxation
when using low valence crosslinkers, while larger supramolecular crosslinkers
bring about much slower dynamics involving a wide distribution of time scales
whose physical origin is still debated. Here, we propose a model where the
relaxation of polymer gels in the dilute regime originates from elementary
events in which the bonds connecting two neighboring crosslinkers all
disconnect. Larger crosslinkers allow for a greater average number of bonds
connecting them, but also generate more heterogeneity. We characterize the
resulting distribution of relaxation time scales analytically, and accurately
reproduce stress relaxation measurements on metal-coordinated hydrogels with a
variety of crosslinker sizes including ions, metal-organic cages, and
nanoparticles. Our approach is simple enough to be extended to any crosslinker
size and could thus be harnessed for the rational design of complex
viscoelastic materials.Comment: 6 pages 5 figures 1 table for the main text and 9 pages 7 figures for
the supplemen