Coalescence of Polymeric Droplets*

Droplet coalescence is an energy minimization process ubiquitous in nature and industry. For Newtonian droplets, the dynamic equilibrium is regime-wise universal with power law exponent b=1 in the viscous regime and b=0.5 in the inertial regime. The neck evolution is governed by the balance of capillary, inertial, and viscous forces. However, our recent study on polymeric droplets has reported the process as regime-dependent. These regimes classified based on concentration ratio c/c* are namely the inertioelastic(IE) c/c*<c_e/c*, viscoelastic(VE) c_e/c*<c/c*<20, and elasticity-dominated(ED) c/c*>20. Our results report the neck evolution radius R to scale as R~t^b, where b is constant in the IE and VD regimes and has a monotonic decrease in the ED regime. Based on this regime-dependent behavior of exponent b, our work proposes a possible novel method named Rheocoalescence to find the characteristic relaxation time λ of polymeric solutions.