Asymmetric freezing behaviors of inclined impact of water droplets on cold hydrophobic surfaces

Solidification of impacting water droplets on surfaces impairs the performance and safety of various applications. Prior studies mostly focused on the freezing behaviors of normal impact of water droplets on cold surfaces. In this work, we explore the freezing morphologies and self-peeling behaviors of water droplets when impacting cold hydrophobic substrates with an inclination angle (45 degrees). To improve the coupling between the solidification and drop-scale hydrodynamics, we thus conducted the experiments in a regime where the heat transfer rate is significantly enhanced for fast solidification. In contrast to hydrophilic surfaces, the final freezing morphologies on hydrophobic surfaces are easier to exhibit a rivulet, whose length has a non-monotonic relation with Weber number. The rivulet morphologies can be transited into an asymmetric fingering pattern when Weber number is high enough. More intriguingly, we observe the asymmetric self-peeling behaviors of water droplets upon impacting cold inclined surfaces, where both ice titled direction and degree are highly dependent on Weber number. Moreover, the maximum ice deflection at the edge is found to agree well with a scaling law.