GIBBS Adsorption Theory at Liquid Interfaces

FIGURE 3.12 Surface composition (A) of pure water, (B) of an ethanol-water solution (shaded = ethanol). 

It can be observed that surface tension decreases due to ethanol. This suggests that there are more ethanol molecules at the surface than in the bulk phase, which is also seen in a cognac glass. The ethanol vapors are observed to condense on the edge of the glass, showing that the concentration at the surface of the solution is very high. 

FIGURE 3.13 Concentration of detergent (shaded with tail) in solution and at the surface. The shaded area at the surface is the excess concentration due to accumulation. 

FIGURE 3.14 Liquid column in a real system with a-phase and (3-phase. 

However, in the idealized system, the chemical compositions of the a and P phases are imagined to remain unchanged right up to the dividing surface so that their concentrations in the two imaginary phases are also cia and clfj, respectively. 

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