Activity-Influenced Drop Evaporation

Active drops, by virtue of their capabilities to self-migrate, have found significant applications in disciplines ranging from designing novel emulsions to explaining bio-locomotion. This study discusses a theory of evaporation of active and nematic extensile drops. The interplay of activity and the mass loss due to evaporation enforces the air-liquid interface to descend and touch the solid substrate (where the drop rests). This results in the formation of punctured drops and the creation of an inner three-phase contact line and donut-shaped drop. A subsequent loss of liquid mass due to evaporation ensures that the contact angle at this inner contact line (ICL) becomes equal to the receding contact angle enforcing a runaway stage (drop dynamics with receding ICL, but pinned outer contact line or OCL) of the drops. The resulting particle deposition results in the formation of ring galaxy like pattern: the ring is at the location of the OCL, while there is a diffuse region of deposited particles following the trajectory of the receding ICL. We also discuss the cases where these phenomena are absent in active extensile drops, and the possible alterations in the drop evaporation lifetime between active extensile versus active contractile drops.