Langmuir
| When a solution of an amphiphile in a water insoluble solvent is placed on a water surface with a micro syringe, the solution spreads rapidly to cover the available area. As the solvent evaporates, a monolayer is formed (see figure 1.). When the available area for the monolayer is large the distance between adjacent molecules is large and their interactions are weak. The monolayer can then be regarded as a two-dimensional gas. Under these conditions the monolayer has little effect on the surface tension of the water. If the available surface area of the monolayer is reduced by a barrier system the molecules start to exert a repulsive effect on each other. This two-dimensional analogue of a pressure is called surface pressure, P, and is given by the following relationship: P = g - g0. Where g is the surface tension in absence of a monolayer and g0 is the surface tension with the monolayer present. |
 Gas Liquid Solid Figure 1. Schematic of the oriëntation of the molecules in different phases. |
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