Results of Film Balance Studies

The preceding section shows that it is possible to determine tt-A isotherms for surfaces just as p- V isotherms may be measured for bulk matter. The results that are obtained for surfaces are analogous to bulk observations also, although some caution must be expressed about an overly literal correlation between bulk and surface phenomena. We return to a discussion of these reservations below. There can be no doubt, however, that analogies with bulk behavior supply a familiar framework within which to consider tt-A isotherms. 

6 Composite two-dimensional pressure ir versus area a isotherm, which includes a wide assortment of monolayer phenomena. Note that the scale of the figure is not uniform so that all features may be included on one set of coordinates. The sketches of the surfactants show the orientations of the molecules in each phase at various stages of compression. 

We are concerned with two-dimensional matter situated at the boundary between two bulk phases. 

The properties of the two-dimensional phases are relatively independent of the properties of the bulk phases of the same material. 

It is not difficult to propose and develop a model for the gaseous state of insoluble monolayers. The arguments parallel those developed in kinetic molecular theory for three-dimensional gases and lead to equally appealing results. The problem, however, is that many assumptions of the model are far less plausible for monolayers than for bulk gases. To see this, a brief review of the derivation seems necessary. 

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