  Recent studies have demonstrated the significant roles of droplet self-spin
motion in affecting the head-on collision of binary droplets. In this paper, we
present a computational study by using the Volume-of-Fluid (VOF) method to
investigate the spin-affected droplet separation of off-center collisions,
which are more probable in reality and phenomenologically richer than head-on
collisions. Different separation modes are identified through a parametric
study with varying spinning speed and impact parameter. A prominent finding is
that increasing the droplet spinning speed tends to suppress the reflexive
separation and to promote the stretching separation. Physically, the reflexive
separation is suppressed because the increased rotational energy reduces the
excessive reflexive kinetic energy within the droplet, which is the cause for
the droplet reflexive separation. The stretching separation is promoted because
the increased droplet angular momentum enhances the local stretching flow
within the droplet, which tends to separate the droplet. The roles of orbital
angular momentum and spin angular momentum in affecting the droplet separation
are further substantiated by studying the collision between two spinning
droplets with either the same or opposite chirality. In addition, a theoretical
model based on conservation laws is proposed to qualitatively describe the
boundaries of coalescence-separation transition influenced by droplet self-spin
motion.
