Superhydrophobic qualities of an aluminum surface coated with hydrophobic solution NeverWet

• Superhydrophobicity of a spray-coated aluminum surface is evaluated through drop impact.
• Impact outcomes and bounce-off characteristics are similar to that on lotus leaf.
• Maximum drop spread on the coated surface is predicted using the model for drop impact on small target surfaces.
• Power dependence of maximum drop spread on We is affected by fingers at high We.
• Fingers affect the trend of drop contact time with We at high We.

Effortless preparation of superhydrophobic surfaces mimicking the wetting characteristics of lotus leaf is of interest to several works. Spray coating methods using hydrophobic solutions are often adopted to realize such superhydrophobic surfaces. The present study investigates the dynamic behavior of impacting water drops on an aluminum surface coated with commercially available hydrophobic solution NeverWet with primary focus to understand the superhydrophobic qualities of the coated surface. The Weber number, We of impacting drop was varied from 1 to 568. The salient features of drop impact dynamics are compared with those of other superhydrophobic surfaces and naturally seen lotus leaf reported in literature. The outcomes as well as the bounce-off characteristics of impacting water drops are comparable to those observed on lotus leaf. The contact time remains almost constant with impact velocity, Uo for 7 < We < 200. The dynamics of impacting water drops on the coated surface is compared with published works on superhydrophobic surfaces prepared using other fabrication methods. The trend of maximum lamella spread factor with We on the coated surface could be predicted using the analytical relation developed for drop impact on small target surfaces ignoring the effect of viscosity. The power dependence of maximum spread factor on We is higher if fingers at the rim of lamella are accounted for in the maximum spread measurements. The number of fingers formed at the rim of lamella at its maximum spread for high We drop impact increases with We which follows the predictions from Rayleigh-Taylor and a modified Savart-Plateau-Rayleigh instability as well as experimental data reported in literature. The findings from the study are useful for works which use NeverWet to develop superhydrophobic qualities on solid surfaces.

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