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A super-hydrophobic aluminum alloy surface with decorated pillar arrays was obtained by hybrid laser ablation and further silanization process. The as-prepared surface showed a high apparent contact angle of 158.2 ± 2.0° and low sliding angle of 3 ± 1°. Surface morphologies and surface chemistry were explored to obtain insights into the generation process of super-hydrophobicity. The main objective of this current work is to investigate the maximum spreading factor of water droplets impacting on the pillar-patterned super-hydrophobic surface based on the energy conservation concept. Although many previous studies have investigated the droplet impacting behavior on flat solid surfaces, the empirical models were proposed based on a few parameters including the Reynolds number (Re), Weber number (We), as well as the Ohnesorge number (Oh). This resulted in limitations for the super-hydrophobic surfaces due to the ignorance of the geometrical parameters of the pillars and viscous energy dissipation for liquid flow within the pillar arrays. In this paper, the maximum spreading factor was deduced from the perspective of energy balance, and the predicted results were in good agreement with our experimental results with a mean error of 4.99% and standard deviation of 0.10.

The bouncing dynamics of droplets with various viscosities on superamphiphobic surfaces is experimentally investigated. It is shown that contact number T ≡ We Re−1/2 can characterize both the maximum spreading factor and the contact time of viscous liquid droplets. Using energy conservation and contact number T, a new theoretical model of the maximum spreading factor for various viscous liquid droplets is proposed. The predictions of this model agree with the experimental results and data from previous studies. Liquid viscosity has a significant effect on the impact process and leads to an increase in contact time. For low-viscosity droplets, contact time is independent of impact velocity, whereas for high-viscosity droplets, contact time increases with increasing impact velocity. Therefore, the new time scaling τ ∼ D0/U0T=ρD03μU0/σ21/2 proposed in our previous work is adopted to characterize the effects of viscosity on contact time. Excellent agreement between the scaling and experimental results is found. These findings should therefore help understand how to design surfaces for a variety of applications, such as anti-icing or reducing heat transfer with impacting liquids.

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