Dynamic characteristics of droplets’ impact on solid surfaces with varied roughness

What is it about?

A high-speed camera capable of recording at 10,000 frames per second is utilized to capture the impact process of droplets on various rough surfaces. The effects of the droplets’ properties, surface roughness, and surface wettability on the dynamic spread of droplets on solid surfaces are investigated. The research demonstrates that the addition of surfactants reduces the surface tension of droplets and dampens their vertical oscillations on surfaces, leading to decrease in the time required to achieve equilibrium. The increase of surface roughness leads to the decrease of droplet retraction degree and the decrease of maximum spreading coefficient. The surface wettability also influences the maximum spread coefficient and equilibrium time. The equations for the maximum spreading coefficient of the droplets on a solid surface with respect to the Weber number (We) and the revised capillary number (Ra*) are obtained by quantitative analysis.

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Why is it important?

From the perspective of solid-liquid interaction, the influence of droplets' physicochemical properties and the inherent features of the solid surface on the kinetic behavior exhibited by the droplets during the impact process are investigated. Compared to previous studies, this study underscores the pivotal role of solid surface roughness as the prime determinant in investigating the intricate interplay between droplet spreading dynamics and surface roughness during the impact process. The We and Ra* are utilized as key variables to derive empirical equations that describe the maximum spreading coefficients of droplets impacting solid surfaces.

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