Universal behaviour in coalescence of polymeric droplets*

One of the most common and frequent rheological phenomena observed in nature is the coalescence of droplets. It encompasses the importance of phenomena like raindrops formation in clouds, printing techniques, and even multiphase flows. The process of merging of two droplets towards forming a single daughter drop is known to exhibit formation of liquid bridge. The dynamics of bridge growth for fluids exhibiting characteristic relaxation time scales like polymer solutions is yet to be probed. In polymeric solutions the interplay between surface-forces along with the inertial, viscous, and elastic forces propel this phenomenon. By the balance of the pertinent forces in the phenomenon, we unveil a universal temporal evolution of the neck radius, R, as R/(ν_oλ)^0.5 ~ (t/λ)^0.36 Oh^-0.36(c/c*)^-0.432. Our findings are substantiated by a theoretical model using linear Phan-Thein-Tanner constitutive equation.