Yi Hui Zhao, Yu Sen Jie, You Cai Xue, Zi Wei Shi, Yuan Chen Dong,

Murugappan Muthukumar^*, Di Jia^*

Nature Communications, 2025, 16, 3247

https://www.nature.com/articles/s41467-025-58571-2

Gels comprised of dynamic bonds are important candidates for the emerging ‘intelligent’ gels due to their unique characteristics arising from the dominance of physical bonds over chemical bonds. Due to the weak interactions driving the physical gel assembly, the structure and dynamics are constantly changing in ways in permanently crosslinked gels. We report a universal law of hierarchical gel dynamics arising from association-dissociation of physical crosslinks, as discerned from dynamic light scattering (DLS) on diverse sets of complex gels. It is the first experimental evidence of a stretched exponential decay with a universal exponent 1/3 in DLS for all the physical gels, complementing more than five decades of DLS studies on conventional chemical gels. This discovery allows identification of whether physical or chemical bonds dominate the crosslinks in complex gels, as well as extraction of local energetics of the constituent physical crosslinks by their characteristic relaxation times. It also enables designable clocks for their large-scale functional properties applicable in broad fields implementing smart hydrogels. Wondering whether there exists any general principle that maps the diversely different chemistries of dynamic bonds into the observed unifying law for large-scale collective dynamical properties of physical gels, we answer affirmatively.