Hydrodynamics-dominated wetting phenomena on hybrid superhydrophobic surfaces
Arash Azimi1, Chae Rohrs1, Ping He1
1Department of Mechanical Engineering, Lamar University, Beaumont, TX 77710, USA.
Hypothesis:
Because of rich local hysteresis, it is a challenge to determine the global minimum surface energy and consequently, the true apparent contact angle of a liquid droplet on chemically-heterogeneous, rough surfaces. Meanwhile, a specific type of wetting phenomena strongly dominated by the hydrodynamic process is expected to be resulted by the chemically-heterogeneous micro-structures, yet not well studied.
Simulations:
A series of micropatterned hybrid substrates, which have the same pillar dimensions but different pillar spacings, have been studied using continuum simulations. The hybrid feature of the micropatterns presented here has two defining facets: the pillar top-surface is highly hydrophilic (SiO2-based), while the pillar side-surface and substrate bottom surface are hydrophobic (Teflon). Different initializations of a 0.4 µL water droplet have been simulated to mimic the experimental measurements, i.e., releasing a stationary droplet near the substrate, impacting the droplet at various speeds, and setting an initial apparent contact angle of 90°.
Findings:
The simulated contact angles agree with the experiments in the literature. Moreover, this study vividly depicts the hydrodynamics-dominated wetting processes, and captures multiple metastable Cassie-Baxter states. This research is applicable to the design of new hybrid superhydrophobic surfaces with special functionality, such as high controllability at varied hydrodynamic conditions.
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