Dynamic behaviors of droplet impact and spreading—Water on glass and paraffin

A water drop was released from 13.6 mm above a glass or paraffin surface. The images were recorded sequentially (the silhouette and 58° top view) from the moment that the droplet impacted solid surface until it reached equilibrium. The full water droplet profile during spreading was obtained from the digitized images. Digitized droplets were then used to detail the dynamic impact and spreading behaviors, including the droplet morphology and the relaxations of wetting diameter, droplet height, contact angle, and spreading velocity.The dynamic wetting behaviors of a water droplet impinging on a hydrophilic and a hydrophobic surface were investigated in this study. Digitized droplet profiles allow one to clarify the independent motion of two related but independent parts, central region and rim, of an impinging droplet. An interesting plateau region on the relaxation of droplet height was observed in the first cycle for both surfaces. For paraffin surface, three particular growth modes in droplet height were detected in each oscillation at early spreading stages. It takes only three oscillation cycles (0.085 s) for the water droplet on glass substrate to dissipate its energy and reach its equilibrium state. On the other hand, the oscillation of the droplet on paraffin substrate lasts 28 cycles (0.266 s). Moreover, several other new phenomena were also observed and discussed in this work.