Changes of Phase and Transformations of Higher Order in Monolayers

Abstract

The gaseous, liquid, mesomorphous and solid states in monolayers are defined and their close connection with the corresponding states in three dimensions rigorously established. This involves a new treatment of the two-dimensional liquid and of its transformation to the mesomorphous state. The properties of the three-dimensional vitreous state of fatty substances are shown to be particularly important in connection with the behavior of monolayers. The different critical and transformation temperatures are also defined and their significance explained. From this is derived a systematic classification of the different types of isotherms observed. By determining the variations of the compressibility, viscosity and apparent dipole moment with change of area, higher order transformations are detected in monolayers. These transformations occur at the same areas as those at which ordinary phase transformations occur at lower temperatures.