The coalescence to stretching separation transition in binary droplet collisions*

The transition from coalescence to stretching separation occurs in binary droplet collisions as the collision off-set (impact parameter) is increased. This work investigates the impact of fluid viscosity on this transition for equi-diameter droplets It shows that the transition is viscosity-independent for Ohnesorge numbers spanning an order of magnitude. The maximum length of coalesced droplet ligand formed prior to stretching separation is 3.35 droplet diameters. Surprisingly this was constant for all conditions tested, i.e. independent of Weber and Ohnesorge number. This observation can be used to develop a simple, robust model of the coalescence-stretching separation transition.