Interfacial dynamics of viscous droplets impacting a superhydrophobic candle soot surface: Overview and comparison

Abstract

The impact of droplets on textured or rough surfaces has garnered remarkable appreciation due to its multifarious applications such as self-cleaning, anti-icing, and anti-fouling, leading to a plethora of engineered superhydrophobic surfaces (SHPs) exhibiting different interfacial dynamics during impact. However, the prime limiting factors in using these surfaces abundantly arise from their long fabrication time and concurrent high cost. Here, we propose using carbon soot nanoparticle (CSNPs) coated fractal superhydrophobic surfaces prepared from flame deposition as an alternative to overcome the limitations. We establish our claim by exploring the dynamic wetting behavior of the soot-coated surface in terms of key droplet impact parameters such as rebounding, contact time, impalement transition, and splashing dynamics. A systematic investigation is undertaken by considering a vast range of viscosity and impact conditions. One of the significant observations is the absence of the partial rebound regime during the impact of water droplets on the CSNPs surface, unlike most of the existing superhydrophobic surfaces under similar impact conditions. Furthermore, the surface promotes droplet splashing for moderately viscous solutions at high impact velocities, also characterized by unified scaling laws based on different non-dimensional numbers. Finally, a regime map is proposed to elucidate the complete dynamic wetting characteristics of these CSNPs' surfaces for viscous fluids, which further reflects competitive and equal, if not superior, wetting behavior compared to a series of existing non-wetting surfaces. The results are expected to promote CSNPs based surfaces in applications such as self-cleaning, oil-water separation, and thermal management.