Experimental investigation of the impact of viscous droplets on superamphiphobic surfaces

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.