Phase changes in Stable Monolayers

The equation of state of a gas shows that under suitable conditions gaseous and condensed states may coexist. When hydrogen gas dissolves in palladium, dilute and condensed phases may exist in equilibrium (67), or when a film of myristic, palmitic, or similar fatty acids is spread upon water, compressed and expanded states can occur together at suitable temperature or pH. of the imderlying liquid (58). It is therefore interesting to inquire whether two phases can occur on stable monolayers on tungsten. 

Using the idea of thermal and electrostatic spreading pressures developed in the previous section, one may write  

F = thermal spreading forced-electrostatic spreading force hT 

The phases discussed here are coexistent in a monolayer. Their constitution therefore differs from that of films of cadmium or mercury on glass (pp. 341 et seq.), where mono-layer systems rearrange themselves into three-dimensional aggregates. An exact analysis, employing statistical mechanics, of conditions yielding a two-dimensional condensed phase or a three-dimensional aggregate would be of importance. Preliminary studies of the behaviour of double layer films have been made by Cemuschi(59) and by Dube(OO). 

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