Microfluidic-assisted growth of colloidal crystals

We investigate the concentration process of dilute dispersions of charge-stabilized colloids using a dedicated microfluidic tool based on evaporation. We observe the nucleation and growth of colloidal crystals with typical dimensions of 10 x 50 mu m(2) x several millimetres whose growth kinetics and structures are characterized using optical, confocal, and electron microscopy. We demonstrate with systematic screening experiments that microfluidics yields a precise control on the growth pace of these dense organized colloidal states. We then predict the growth rate of these colloidal structures with a model of the suspension (hard-spheres) that accounts for a diverging collective diffusion coefficient near the close-packing; this description helps us understand why the kinetics can be anticipated on the basis of a simple conservation law. Finally, our experiments unveil the important role played by ions which are also present in the initial dilute dispersion and therefore also get concentrated simultaneously with colloids, and their influence on the ordering.