ABSTRACT
The liquid state of matter plays a very important role in everyday life, and the liquid surface has a dominant role in many phenomena. In fact, about 70% of the surface of Earth is covered by water. The most fundamental characteristic of liquid surfaces is that they tend to contract to the smallest surface area to achieve the lowest free energy. Whereas gases have no definite shape or volume, completely filling a vessel of any size containing them, liquids have no definite shape but do have a definite volume, which means that a portion of the liquid takes the shape of that part of a vessel containing it and occupies a definite volume, with the free surface plane except for capillary effects where it is in contact with the vessel. This is evident in rain drops and soap films, in addition to many other systems that will be mentioned later. The cohesion forces present in liquids and solids and the condensation of vapors to liquid state indicate the presence of much larger intermolecular forces than the gravity forces. Furthermore, the dynamics of molecules at interfaces are important in a variety of areas, such as biochemistry, electrochemistry, and chromatography. The degree of sharpness of a liquid surface has been the subject of much discussion in the literature.
