Abstract
Hemiwicking has been introduced to describe the wetting state in which a liquid film surrounds a drop. To fully understand this special wetting state, we performed energy analysis and systematic lattice Boltzmann (LB) simulations on the wetting state through spreading liquid droplets on pillared hydrophilic substrates. Although the energy analysis shows that the hemiwicking is energetically unfavorable, droplets in stable hemiwicking are indeed observed in our LB simulations. This observation led us to conclude that we have obtained a result that is the same as the result obtained in the published experiment and theory: hemiwicking is dynamically trapped by the pinning of the imbibition front during invasion of the substrate texture by the liquid film. Our simulations show that the special wetting state is always found to emerge near the phase boundary between the liquid film and the Wenzel state. For the morphology of the droplet, strong deviation of the apparent contact angle from hemiwicking is observed when the contact line of the liquid imbibition film is close to the spherical caplike droplet. We also show that there exist at least two different kinetic pathways for the formation of hemiwicking, including spreading and evaporation.
Highlights
Controlling wettability of textured substrates is an important aspect of material science and surface chemistry, which has a variety of practical applications in industry, agriculture, and daily life
When a liquid droplet is in contact with a textured substrate, it can stay either in a Cassie state with gaseous pockets trapped inside substrate roughness or in a Wenzel state with liquid penetrating the roughness.[1,2]
We first performed thermodynamic analysis on the stability of hemiwicking for droplets on the hydrophilic textured substrates, by comparing their energies with those corresponding to the Wenzel state and the complete wetting state, by a method similar to that used by Ishino et al.[29]
Summary
Controlling wettability of textured substrates is an important aspect of material science and surface chemistry, which has a variety of practical applications in industry, agriculture, and daily life. We first performed thermodynamic analysis on the stability of hemiwicking for droplets on the hydrophilic textured substrates, by comparing their energies with those corresponding to the Wenzel state and the complete wetting (liquid film) state, by a method similar to that used by Ishino et al.[29]
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