Unraveling the influence of polymer brush thickness on droplet impact behavior on quasi-liquid surfaces

The droplet impinging dynamics on surfaces represent a key phenomenon in various engineering and industrial applications, such as anti-icing, droplet electricity generation, printing. Understanding this phenomenon can assist in optimizing fabrication procedure and enhancing performance in these applications. Recently, quasi-liquid surfaces (QLS) prepared by grafting flexible polydimethylsiloxane (PDMS) chains onto substrate surfaces have garnered widespread attention due to their unique liquid repellency and excellent durability. These surfaces have shown outstanding potential in various industrial applications, including anti-icing and steam condensation. The QLS can be fabricated with different thicknesses under varying conditions, which could influence the surface wetting properties and droplet impinging dynamics on the surfaces. In this work, we utilized high-speed cameras to capture the dynamic impact behavior of water droplets on QLS surfaces with varying thicknesses and structures. By studying the transverse and longitudinal dynamic responses of the droplets, we obtained the energy dissipation during the impact process. Previous reports indicate that smoother surfaces result in less energy loss and higher rebound heights during droplet impact. In our experiments, although thicker QLS provides smoother surfaces, they exhibit greater energy dissipation. This suggested that the QLS could act as a soft cushion and absorb a portion of the kinetic energy during the impact process. These findings can be used to guide the selection of optimal preparation processes tailored to the specific requirements of various industrial applications, including inkjet printing, spray coating, and spray cooling technologies aiming to achieve the best droplet impact characteristics.