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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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Dense silty sediments exhibit complex rheological behaviors due to their particular sediment composition, which consists of sand, silt and clay. This paper investigated the rheological properties of ten dense silty sediments prepared with various percentages of kaolin. A set of rheological experiments was conducted with an MCR302 rheometer. Measurements of the flow curves, deformation curves, and shear stress-time response were made. The dense silty sediments underwent a solid-liquid transition during shear rate ramp tests, and the critical shear stress increased with decreasing median particle diameter D50. Thixotropy was common in the samples with smaller D50, but the samples with larger D50 displayed anti-thixotropic behavior. Both the power-law model and the Herschel-Bulkley model were selected to describe the rheological behavior, and the Herschel-Bulkley model was more suitable for samples with higher density and smaller D50. The parameters in the empirical expressions for calculating rheological parameters were obtained by a regression analysis.