Well solid - solid interfaces are more complicated.
Don't forget that true solids have a regular crystalline structure so are constrained to their particular crystal shape. They are not so readily deformable as fluids by boundary pressure forces. Their boundaries don't just follow the interplay of pressure forces between two fluids.
In thermodynamics when discussing polyphase solids such as alloys you have to add an extra term into the First Law for to allow for the surface energy of the grain boundaries.
Perhaps more detail about what you are looking for?