Abstract:
The impact dynamics and spreading behavior of droplets impinging on structured superhydrophobic surfaces are dependent on both the droplet initial conditions and the surface texture. The
equivalence of wetting and dewetting pressures is classically known to be a critical factor in determining
the state of a droplet during the contact and spreading phases. The present study extensively examines the
underlying physics behind this pressure balance during the impact process and its direct role in determining the wetting process. Extensive three-dimensional simulations employing droplet impact on a structured
superhydrophobic surface has been performed to reveal the intricacies of the interactivities of the fluid with
the microstructure. Insight onto the acute role of wetting pressures and the implications of the same on
determining the wetting dynamics, with internal fluidics of the droplet during the impact process, has been
discussed. The phenomenon of state transition from the Cassie-Baxter to the Wenzel up on impact is also
investigated and the intricate flow mechanics at play within the posts has been presented. Knowledge of
pressure distribution and internal flow structures within the droplet during its interaction with the surface
at different instances of time reveals the root mechanism behind the impalement of the droplet to a fully
wetting state. Analysis of the internal pressure and flow distribution also presents necessary justification
for the existence of a partially impaled state. The time evolution of spread for different scenarios is in
agreement with experimental results and the article provides insight onto the role of wetting pressure in
determining fluidic interactions on such surfaces.
