  Internal recirculation in a moving droplet plays an important role in several
droplet-based microfluidic devices as it enhances mixing, chemical reaction and
heat transfer. The occurrence of fluid slip at the wall, which becomes
prominent at high shear rates and lower length scales, results in a significant
change in droplet circulation. Using molecular dynamics (MD) simulations, the
presence of circulation in droplets is demonstrated and quantified. Circulation
is shown to vary inversely with slip length, which is a measure of interface
wettability. A simple circulation model is established that captures the effect
of slip on droplet circulation. Scaling parameters for circulation and slip
length are identified from the circulation model which leads to the collapse of
data for droplets with varying aspect ratio (AR) and slip length. The model is
validated using continuum and MD simulations and is shown to be accurate for
droplets with high AR.
