Impact and wetting of polysilazane droplets on a metal surface

Spray coating with liquid polymers is a crucial step in producing polymer-derived ceramic (PDC) coatings before curing the precursor. However, the interactions between polymer droplets and target surfaces during the spray coating process have not been adequately characterized in existing literature. This experimental study aims to comprehensively examine the previously unknown droplet impact dynamics for a specific ceramic precursor, Polysilazane, on Inconel surfaces. The diameter of Polysilazane droplets was kept constant, while their impact velocity was varied to achieve different impact conditions. The same parameter range was also explored with water, water-glycerol, and ethanol droplets for comparison purposes. High-speed videos were captured to observe the instantaneous impact process, while low-speed videos were recorded at specific instances to document the gradual wetting process at later stages. The investigation revealed unique spreading dynamics of Polysilazane droplets, including smooth contact angle variation during the transition from impact to lateral spreading, absence of delayed wetting, no formation of wavy structures on the droplet interface during spreading, and no retraction process within the studied conditions (Weber number up to 1200). Conversely, Polysilazane displayed similarities in the normalized spreading curves with other liquids. Additionally, the maximum spread factor of Polysilazane could be well predicted using existing universal scaling models designed for different liquid types. Lastly, Polysilazane exhibited a distinctive post-impact wetting process that persisted for an extended duration. The wetting dynamics of Polysilazane could be effectively described by an empirical exponential law originally developed for partial wetting systems. [Display omitted]