ABSTRACT
In the case of partial wetting, the spreading proceeds after deposition until the static advancing contact angle is reached through “caterpillar motion,” which requires much less energy and, hence, results in faster spreading. The dynamics of the droplet is defined by two competing mechanisms: spreading, which results in an extension of the droplet base, and evaporation, which results in a shrinkage of the droplet base. The spreading/evaporation processes were captured at 60 frames per second for the whole experiment duration using two video cameras, which simultaneously captured a side view and a view from above. A theoretical model was developed to account for the spreading/evaporation process, which produced universal theoretical curves for the radius, contact angle, volume, and spreading/evaporation velocities on time. Simultaneous spreading and evaporation of droplets of trisiloxane solutions over hydrophobic substrates were studied both experimentally, using a video-microscopy technique, and theoretically.
