  Recent investigations on the coalescence of polymeric droplets on a solid
substrate have reported strong disagreements; the heart of the issue is whether
coalescence of polymeric drops is similar to that of Newtonian fluid and is
independent of molecular relaxation, or whether the role of entanglement of
polymeric chains leads to a transition kinetics different from that of
Newtonian fluid. Via this report, we resolve the disagreements through a
discussion on the effects of merging method on the dominant forces governing
the coalescence process, i.e., inertia, dissipation, and relaxation. Our study
unveils that the coalescence dynamics of polymeric drops is not universal and
in fact, it is contingent of the method by which the coalescence is triggered.
Additionally, we demonstrate the spatial features of the bridge at different
time instants by a similarity analysis. We also theoretically obtain a
universal bridge profile by employing the similarity parameter in a modified
thin film lubrication equation for polymeric fluids.
