  We investigate the retention force factor of sessile droplets of pure
(ethanol) and binary (water-ethanol) fluids laden with alumina nanoparticles
placed on a critically inclined substrate. It is observed that while the
critical angle of an ethanol droplet increases with an increase in
nanoparticles concentration, for water-ethanol binary droplets, it reaches to
plateau and decreases slightly after 0.6 wt.\% nanoparticle loading. The effect
of composition and concentration of nanoparticles on the retention force factor
is studied, and correlations are proposed for the retention force factor and
critical angle for pure and binary droplets. Infrared images of evaporating
droplets of pure and binary fluids reveal richer hydrothermal waves in droplets
with nanoparticles loading than in droplets without loading, and these waves
are more intense in pure ethanol droplets. On an inclined substrate, the body
force caused the droplets to elongate more toward the receding side, which led
to an earlier breakup of the droplet at the receding side. To the best of our
knowledge, our study is a first attempt to investigate the retention force
factor for the droplets loaded with nanoparticles on an inclined substrate.

Fluid Dynamics