DYNAMIC CONSIDERATIONS IN THE CLOSING AND OPENING OF HOLES IN THIN LIQUID-FILMS

Whether holes in thin films close or open is an important issue in the design of liquid coatings. Previous analyses, for example the work of Taylor and Michael (J. Fluid Mech. 58, 625 (1973)) predict a static criterion for hole closure based on a balance between capillary and gravitational forces. In the present work we develop a numerical model which follows the evolution of holes to determine whether they close or open. The model is based on the lubrication approximations and requires input of the advancing and receding contact angles. Because viscous forces are also included in the present model, the static criteria can be reevaluated using the more complete theory. We find that holes which the static criteria predict will close can actually open, and vice versa. © 1993 by Academic Press, Inc.