Generation, migration, and coalescence of droplets: A state-of-the-art review from the perspectives of wettability, inertia, and electric field

Generation, migration, and coalescence of droplets are some of the fundamental phenomena observed in multiphase microfluidic devices that offer widespread application in interdisciplinary platforms. These phenomena are governed by involved interfacial forces, and tuning these forces through active or passive techniques has emerged as a thriving research domain. Among the available strategies for interfacial force modulation, wettability, electric field, and inertia are some of the key factors that are paid attention as they are largely involved in naturally occurring phenomena and widely applied in technically designed platforms. Motivated by these, this work reviews the studies carried out in the domain of surface wettability and its influence on two-phase flow, to the electrically tuned migration and deformation characteristics of compound drop, and thereafter towards the inertia modulated coalescence dynamics of compound drop, and also explores several unresolved facets that can be addressed by the research community.