Mixtures of colloids and wormlike micelles: Phase behavior and kinetics

We have studied equilibrium phase behavior and nonequilibrium particle aggregation in a mixture of charged colloids and ionic wormlike micelles. At high enough concentration of micelles but below the overlap concentration (c*), separation into coexisting colloidal gas and liquid phases occurred. Beyond c*, we observed rapid, nonequilibrium aggregation of the particles to form transient gels. These space-filling structures can show rapid gravitational collapse after an initial latency period, a behavior also found in model colloid-polymer mixtures at high polymer concentrations. The depletion mechanism was found to play an important role in phase separation. Diffusing wave spectroscopy (DWS) was used to study the dynamics of a transient gel. After about one-half of the latency period, the fluctuations in the scattered intensity increased significantly. The particle dynamics slowed during the whole latency period, consistent with the aging of the gel structure. After gravitational collapse, a very broad, logarithmic decay of the correlation function was detected for the sediment.