(93a) Shape and Stability of Liquids That Partially Wet Solids

The shape at rest of a liquid that partially wets a solid depends
on the contact-angle at the three-phase common line.  Moreover, in the absence of other forces, the relative
affinities of the triplet of materials (liquid, solid and gas) predicts the
entire shape of the liquid at equilibrium and its stability depends on the
mobility of the contact-line, as is well-known.  What seems not as well-appreciated
is that, for mobile contact-lines, fully three-dimensional shapes can be more stable than axisymmetric
shapes.  For example, a mobile
axisymmetric sessile drop on a planar substrate can be unstable to a
non-axisymmetric shape.  
These observations have a number of fundamental implications for the
inviscid spreading behavior of drops and rivulets on solids.   We shall illustrate these in this
talk.