Impinging Core-Shell Compound Droplets on Superamphiphobic Surfaces

Recently, increasing interest has been shown in the impact of compound droplets due to its various applications and academic significance. However, the study of compound droplets is largely focused on their spreading stages or the impact on hydrophilic and weak hydrophobic surfaces. Here, we perform an experimental investigation on the impact of oil-inwater compound droplets on superamphiphobic surfaces. Compound droplets with different oil volumetric ratios were produced, aiming to reveal the effect of the oil volumetric ratio on the whole impact dynamics including the impact phenomena, quantitative spreading, pinning, and retraction processes. The oil volumetric ratio shows dramatic influence on the impact phenomena: the damping of the capillary wave is enhanced, the bubble entrapment can be suppressed, and water entrapment inside the oil core can be observed in a certain Weber number range. It is found that the spreading process of the compound droplet is mainly determined by the Weber number and the additional oil-water interface has no obvious effect within the scope of our research. However, the oil core can accelerate the retraction process, which reduces the contact time.