Emergence of Multiscale Dynamics in Colloidal Gels

Abstract: To gain insight into the kinetics of colloidal gel evolution at low particle volume fractions $\phi$, we utilize differential dynamic microscopy to investigate particle aggregation, geometric percolation, and the subsequent transition to nonergodic dynamics. We report the emergence of unexpectedly rich multiscale dynamics upon the onset of nonergodicity, which separates the wave vectors $q$ into three different regimes. In the high-$q$ domain, the gel exhibits $\phi$-independent internal vibrations of fractal clusters. The intermediate-$q$ domain is dominated by density fluctuations at the length scale of the clusters, as evidenced by the $q$-independence of the relaxation time $\tau$. In the low-$q$ domain, the scaling of $\tau$ as $q^{-3}$ suggests that the network appears homogeneous. The transitions between these three regimes introduce two characteristic length scales, distinct from the cluster size.