Hydrophobic particle coating for enhanced droplet deposition

Abstract

Hypothesis: Droplet deposition on hydrophobic surfaces is highly inefficient due to their low surface energy, leading to significant losses in applications such as pesticide delivery and spray cooling. Conventional approaches rely on surfactants and polymers, which pose environmental and health risks. We hypothesize that coating droplets with hydrophobic particles (Liquid Marbles, LM) enhance deposition efficiency by increasing energy dissipation through particle jamming and suppressing excessive droplet stretching.

Experiments: We investigated the impact behavior of Liquid Marbles on surfaces with varying wettability (contact angles up to 140°) and compared their deposition efficiency to that of bare droplets. The deposition dynamics were analyzed using high-speed imaging, and energy dissipation mechanisms were examined through theoretical modeling. Additional studies were conducted to assess the effects of particle mass loading, substrate flexibility, and alternative biocompatible particles such as Lycopodium and Zein.

Findings: Liquid Marbles significantly improved deposition efficiency, achieving over 95 % deposited volume on surfaces where bare droplets deposited less than 5 %. The enhancement is attributed to increased energy dissipation-up to 50 % higher than bare droplets-caused by particle jamming during recoil. LM also suppressed partial deposition by preventing excessive droplet stretching. The deposition method was effective on both rigid and flexible surfaces, demonstrating potential applications in pesticide delivery and coatings. Furthermore, sustainable alternatives like Lycopodium and Zein enhanced deposition, offering an eco-friendly solution. These findings introduce a surfactant- and polymer-free approach for efficient droplet deposition on nonwetting surfaces.

Keywords: Droplet deposition; Energy dissipation; Hydrophobic surfaces; Liquid marbles; Sustainable particle coatings.