Dynamical Clustering and Band Formation of Particles in a Marangoni Vortexing Droplet

Banded Marangoni Vortexing in Evaporating Droplet

Drying a droplet containing microparticles results in the deposition of particles in various patterns, including the so-called “coffee-ring” pattern. The particle deposition is dependent on the internal flow dynamics, such as the capillary flow and Marangoni vortex (MV), of the droplet. Particle migration and self-assembly on a substrate are interesting phenomena that have critical implications in many applications such as inkjet printing, coating, and many other droplet-based industrial processes. In this work, we observed the formation of bands of particles in a rotating MV during the evaporation of a water droplet containing particles. We investigated the mechanism underlying the formation of banded MV caused by capillary meniscus forces between two particles near the air–liquid interface. In particular, we show that the banded MV can be manipulated by tuning the surfactant concentration and particle concentration. Our findings would provide a new direction in understanding the particle deposition pattern of a colloidal droplet.