Thermally driven dynamics of interacting droplet-pairs in micro-confined shear flow: Beyond the realm of droplet coalescence

Pattern formation and dynamics of interacting droplets in confined passages are ubiquitous in a variety of natural, physical, and chemical processes and appears to be contrasting as compared to single droplet dynamics. However, while the dynamical evolution of single droplets under various forces, including their thermally driven motion, has been explored extensively, the concerned physical facets cannot be trivially extended for addressing the motion of multiple droplets. By considering temperature-gradient-driven interfacial transport, here, we unveil four different modes of thermally activated migration of a droplet-pair in microchannels. These include pure reversing motion, sliding-over motion, follow-up motion, and direct coalescence. The presence of follow-up motion, because of the imposed temperature gradient, has not been investigated before. We further put forward the possibility of conversion of one pattern to another by modulating different tuning parameters, such as the wall temperature, channel dimension, and the relative initial positioning of the droplets. These results may turn out to be of profound importance in a wide variety of applications ranging from materials processing to micro-reactor technology.