Different behaviors of delayed fusion between drops with miscible liquids.

Fusion of sessile droplets with body of different liquids is delayed when the approaching drops are sitting on a highly wettable solid substrate. Owing to the surface tension gradients between the mixing drops, a Marangoni driven flow through the connecting channel appears. Experiments of delayed coalescence were recently reported in [Langmuir 24, 6395 (2008)10.1021/la800630w] for millimeters sized drops. For droplets of submillimeter dimensions, capillary forces dominate. The control of interfacial energies becomes an important strategy for manipulating tiny droplets along the solid surfaces. In this paper we present phase field simulations in two spatial dimensions for microdroplets of perfectly miscible liquids. For drops with a given geometry, systematic investigations were performed for different fluid viscosities. Different behaviors are observed from chasing droplets to droplets repelling.