Disintegration Behavior of Droplets Impacting Hydrophilic Fibers

Droplet disintegration behavior on slender cylindrical objects is critical in various applications. This work investigates droplet impact dynamics on hydrophilic cylindrical glass fibers by using a high-speed imaging method. The influences of liquid viscosity, surface roughness, and surface tension are examined, revealing two distinct disintegration patterns: T-shaped and wing-like. T-shaped disintegration is a never-reported phenomenon that only occurs under very low viscosities, whereas wing-like disintegration tends to appear under higher viscosities and challenges the previous understanding that high viscosity promotes liquid wrapping on fibers. A regime map is constructed by varying impact velocity and liquid viscosity, and an empirical threshold model is proposed. Besides, surface roughness can also enhance wing-like disintegration, equivalent to the effect of directly increasing liquid viscosity. Additionally, a second regime map is developed by varying impact velocity and surface tension, and a theoretical threshold model based on the Plateau-Rayleigh theory is established. This work extends the understanding of droplets impacting fibers, illustrating that droplet disintegration is not necessarily favored by low-viscosity droplets or by surface hydrophobicity.