Nucleated phases migrate by growing in size

Evaporating drops of the PEG and dextran mixture demonstrate fascinating physics at their drop edges. As the drop evaporates, dextran phase nucleates at the contact line (drop edge). These nucleated microdroplets experience a force due to interfacial gradients on their surface. this force drives them towards the center of the drop. Interestingly, however, these microdroplets cannot move continuously. They perform a stepwise motion. They can advance towards the center only by growing in size. This is because there is an opposing flow in the drop acting against their migration. However, by growing, they increase their Marangoni force (a force due to the interfacial tension gradient). But the microdroplets have to wait for a coalescence with another one to increase the size. This scenario provides them with a stepwise motion.

Published in Soft Matter, 2024,20, 8260-8266