Evaporation and Deposition of Colloidal Binary Droplets

Droplet evaporation is a versatile process to deposit solute materials on a substrate unless it induces solute accumulation at droplet perimeter because of outward capillary flows. Despite many efforts to generate inward Marangoni flows to suppress outward capillary flows, it is challenging to control Marangoni flows in colloidal droplets that include binary solvents. To understand and manipulate Marangoni flows in colloidal binary droplets, we investigate droplet evaporation and deposition dynamics by changing the mass ratio of binary solvents. We show that island deposits emerge when Marangoni flows overwhelm capillary flows during most evaporation. The formation of island deposits in colloidal binary droplets would be a helpful route to achieve uniform deposits of colloidal particles or nanoparticles.