Stability and retention force factor for binary-nanofluid sessile droplets on a inclined substrate

TL;DR

This study explores how nanoparticle-laden droplets behave on inclined surfaces, revealing effects on critical angle, retention force, and evaporation patterns, with new correlations for pure and binary fluids.

Contribution

It is the first study to analyze the retention force factor of nanoparticle-loaded droplets on inclined substrates, proposing new correlations for pure and binary fluids.

Findings

Critical angle increases with nanoparticle concentration in ethanol droplets.

Plateau and slight decrease in critical angle for water-ethanol droplets after 0.6 wt.% nanoparticles.

Richer hydrothermal waves observed in nanoparticle-loaded droplets.

Abstract

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.