Deposition pattern of interacting droplets

• Drying pattern of droplets is influenced by droplet interaction.
• Non-uniform deposition pattern is observed for two droplets drying adjacent to each other.
• Presence of a neighboring droplet influences the evaporation flux on the droplet surface.
• The convection pattern is asymmetric in two droplets configuration.

A colloid droplet having pinned contact line forms a ring pattern after drying. The ring pattern of a single droplet shows uniform deposit along the contact line. When two droplets dry adjacent to each other, the deposition pattern is influenced by the presence of the neighboring droplet. The deposition pattern at the nearest region of the two droplets shows weak deposit compared to the rest of the region. The drying pattern in two-droplets configuration is related to the convection phenomena inside the drying droplet and the influence of the neighboring droplet. We have experimentally studied the effect of a neighboring droplet on the convection pattern inside the evaporating droplet using μ-PIV technique to explain the influence of transport phenomena on the drying pattern. COMSOL simulation has also been carried out for understanding the evaporation process. The evaporation rate from the nearest region of the two droplets is lower compared to the rest of the region. Therefore, less number of particles are transported to this region due to low fluid flow causing less deposits in this region. The flow field inside a droplet in the presence of a neighboring droplet shows asymmetric convection pattern unlike single droplet where flow field is symmetric. This convection behavior correlates well with the evaporation flux distribution on the droplet surface and drying pattern.

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