Canthotaxis/Wetting Barriers/Pinning Lines

Abstract

Under conditions of weightlessness, the shape of a capillary surface is determined by the container shape and the contact angle of the liquid with the adjacent solid faces. The location and handling of liquids require the application of wetting aids and wetting barriers such as sharp edges or coatings. At a wetting barrier, the liquid surface winds from the contact angle with the better-wetting face to the contact angle with the worse-wetting face. This effect has been termed “canthotaxis”. Hitherto, canthotaxis has been an art rather than a science; exact results are scarce. Numerically, the length of the interval of canthotaxis (pinning interval) is proportional to the square of the angular interval in question. For surfaces with zero capillary pressure, the length of the interval of canthotaxis varies in proportion to the cube of the angular interval.