Droplet splash and spread on superhydrophobic lotus leaves: Direct regulation by tuning the chain length of surfactant

Impact and spread of droplet on superhydrophobic surface are ubiquitous in inkjet printing, pesticide spraying, paint coating, and other fields. However, due to the extremely water-repellent properties of superhydrophobic surface, droplets frequently splash or roll off, causing great waste and serious environmental problems. Thus, searching for an effective strategy to regulate the droplet splash and spread on superhydrophobic surfaces is of remarkable significance. To address the above issues, herein, we demonstrate the controllable regulation on superhydrophobic lotus leaf surface by tuning the double-chain length of surfactants. The outcomes indicate different regularities for droplet splash in a short time (~10 ms) and spread in a relatively long period (~100 s). It can be concluded that dynamic surface tension of surfactant, diffusion rate of surfactant from the bulk to the interface, and assembly disaggregation rate dominate the impact process, whereas the adsorption kinetic and effectiveness of surfactant along with the spreading driving force determine the wetting transition. Surfactant owning suitable hydrophilic and hydrophobic ratio, fast diffusion rate, and unstable assembly could inhibit droplet splash and improve spreading pronouncedly, thereby enhancing the droplet deposition on superhydrophobic surfaces. This study makes original contribution to screen suitable surfactants from the structural aspects, especially double-chain length, which has not been treated in much detail to date. Our work not only creates a big impetus in illuminating the mechanism of surfactant molecular structure on droplet deposition processes but also greatly expands the applications of surfactant in many fields.