We have examined the formation and dissolution of gels composed of intermediate volume-fraction nanoparticles with temperature-dependent short-range attractions using small-angle x-ray scattering, x-ray photon correlation spectroscopy, and rheology to obtain nanoscale and macroscale sensitivity to structure and dynamics. Gel formation after temperature quenches to the vicinity of the rheologically determined gel temperature, $T_{\text{gel}}$, was characterized via the slowdown of dynamics and changes in microstructure observed in the intensity autocorrelation functions and structure factor, respectively, as a function of quench depth ($\mathrm{\Delta }T=T_{\text{quench}}-T_{\text{gel}}$), wave vector, and formation time $t_f$. We find the wave-vector-dependent dynamics, microstructure, and rheology at a particular $\mathrm{\Delta }T$ and $t_f$ map to those at other $\mathrm{\Delta }T\mathrm{s}$ and $t_f\mathrm{s}$ via an effective scaling temperature, $T_s$. A single $T_s$ applies to a broad range of $\mathrm{\Delta }T$ and $t_f$ but does depend on the particle size. The rate of formation implied by the scaling is a far stronger function of $\mathrm{\Delta }T$ than expected from the attraction strength between colloids. We interpret this strong temperature dependence in terms of cooperative bonding required to form stable gels via energetically favored, local structures.

• Received 28 April 2017

DOI:https://doi.org/10.1103/PhysRevLett.119.178006