(325f) Universal Scaling of Quench-Dependent Dynamics in Intermediate Concentration Colloidal Gels

Ramakrishnan, S., FAMU-FSU College of Engineering
Bahadur, D., Florida State University
We have examined the formation and dissolution of gels composed of intermediate volume fraction nanoparticles with temperature-dependent short-range attraction using small-angle xray scattering (SAXS), x-ray photon correlation spectroscopy (XPCS), 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 Tgel was characterized via the slow-down of dynamics observed in the intensity autocorrelation functions (g2) as a function of quench depth (DeltaT = T -Tgel), wave vector, and formation time (tf). We find self-similarity in the slow-down of dynamics that maps the wave-vector-dependent dynamics at a particular DT and tf to that at other DTs and tfs via an effective scaling temperature, Ts. A single Ts applies to a broad range of DeltaT and tf but does depend on the particle size. The rate of dynamical evolution implied by the scaling is a far stronger function of DeltaT than the attraction strength between colloids. We interpret this strong temperature dependence as collective particle motion possibly arising from rearrangements of energetically-favored locally structures observed in confocal microscopy and via simulations.