Slow dynamics of a soft glassy colloidal suspension in the presence of less mobile regions

Sonali Kawale, Sayantan Chanda and Ranjini Bandyopadhyay

Rheo-DLS lab, Raman Research Institute, Bengaluru, India

Supercooled liquids, in general, show increase in their viscosities and structural relaxation times when quenched rapidly towards their glass transition temperatures. In this work, the dynamics of aging Laponite suspensions (a model glass former) with dispersed polystyrene (PS) beads used as probe particles, is studied in dynamic light scattering (DLS) experiments. In an earlier work, our group had demonstrated a one-to-one mapping between the aging time of a colloidal Laponite suspension and the inverse of the temperature of a molecular glass. Intensity autocorrelation functions measured in DLS experiments show the existence of two-step relaxation processes in these suspensions. The PS beads, being less mobile and larger in size than the Laponite particles, diffuse very slowly and act as nearly pinned particles in the Laponite suspension, with the diffusion time of PS beads being significantly higher (nearly two orders of magnitude) than Laponite particles. The fragility parameter D and Vogel time tαꚙ, which quantify the approach of the aging Laponite suspension towards eventual kinetic arrest, are calculated from the evolution of the structural relaxation time for different concentrations and sizes of the PS beads. Initial experiments suggest a good match of our experimental data with existing theoretical predictions.

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