Collective diffusion coefficient of a charged colloidal dispersion: interferometric measurements in a drying drop

Abstract

In the present work, we use Mach-Zehnder interferometry to thoroughly investigate the drying dynamics of a 2D confined drop of a charged colloidal dispersion. This technique makes it possible to measure the colloid concentration field during the drying of the drop at a high accuracy (about 0.5%) and with a high temporal and spatial resolution (about 1 frame/s and 5 $\mu$m/pixel). These features allow us to probe mass transport of the charged dispersion in this out-of-equilibrium situation. In particular, our experiments provide the evidence that mass transport within the drop can be described by a purely diffusive process for some range of parameters for which the buoyancy-driven convection is negligible. We are then able to extract from these experiments the collective diffusion coefficient of the dispersion $D(\phi )$ over a wide concentration range $\phi =0.24$-$0.5$, i.e. from the liquid dispersed state to the solid glass regime, with a high accuracy. The measured values of $D(\phi )\simeq 5$-$12D_0$ are significantly larger than the simple estimate $D_0$ given by the Stokes-Einstein relation, thus highlighting the important role played by the colloidal interactions in such dispersions.

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Cited by in corpus (4)

• Microfluidic osmotic compression of a charge-stabilized colloidal dispersion: Equation of state and collective diffusion coefficient
• A double rigidity transition rules the fate of drying colloidal drops
• Time-resolved rheometry of drying liquids and suspensions
• Confined drying of a binary liquid mixture droplet: A quantitative interferometric study under humidity control