Effect of suspended particles on the drying process of a carrier-fluid droplet sitting on a solid surface.

We focus on an evaporation process of a volatile droplet on a temperature-controlled solid substrate. The process is strongly affected by suspending tiny particles inside the droplet, resulting in a well-known phenomenon called the "coffee stain problem." The target systems in this study are (1) the water-hydrophilic particle and (2) the water-ethanol mixture-hydrophilic particle. Spatio-temporal particle motion in the induced flow in the evaporation process is visualized by applying three-dimensional particle tracking velocimetry. The correlation between the particle behavior in the evaporation process and the morphological pattern of the droplet after dryout is also discussed.