Rupture of thin liquid films sprayed on solid surfaces

Abstract

An experimental study was done to observe the formation of thin films by spraying liquid onto a solid surface and to determine the conditions under which the films would rupture or remain stable. Water, or water mixed with 20–70 % by weight of glycerin, was sprayed for varying lengths of time onto a circular, 165-mm-diameter plate made of either Plexiglas, steel, or Parafilm-M and the motion of the liquid recorded using a high-speed camera. Water films ruptured immediately after the impact near the center of the surface. Then, if the film thickness was greater than a critical value, the water flooded back and the hole closed; otherwise, the hole remained in the water layer. The critical film thickness increases linearly with advancing liquid–solid contact angle. Increasing liquid viscosity by adding glycerin had little effect on critical film thickness, but inhibited spreading of the liquid and suppressed initial rupture of the liquid layer. A surface energy model was used to predict the variation of critical film thickness with surface wettability.