Flow triggered by instabilities at the contact line of a drop containing nanoparticles

Mass transport in an evaporating colloidal drop is believed to occur via two flow mechanisms: capillary flow due to evaporation and Marangoni flow due to surface tension gradients. We describe a new mechanism for inward mass transport: circulatory fluid flow triggered by a series of pinning-depinning events at the contact line of a drop containing nanoparticles. This flow can be controlled by varying the nanoparticle concentration, and by tuning the solution surface tension.