Gibbs Adsorption Equation in Solutions

This may be compared to a sandwich kind of structure. It is important to mention that these babble structures are of nanometer dimensions, but still easily visible to the naked eye. It also indicates the self-assembly properties of snch SASs. 

The thermodynamics of snrface adsorption has been extensively described by Gibbs adsorption theory (Chattoraj and Birdi, 1984 Spaull, 2004 Zhou, 1989). Further, Gibbs adsorption theory has also been applied in the analyses of diverse phenomena (snch as solid-liqnid or Uqnidj-liqnidj, adsorption of solute on polymers, etc.). In fact, in any systan where adsorption takes place at an interface the Gibbs theory will be applicable (such as solid-liquid protein molecnle-solntion with solutes that may adsorb). 

FIGURE 1.30 Surface composition (a) of pure water and (b) of an ethanol-water solution (shaded = ethanol). 

FIGURE 1,31 Concentration of detergent (shaded with tail) in solution and at surface. The shaded area at surface is the excess concentration due to accumulation. 

Change in the surface tension of water on the addition of different solutes  

If one adds an inorganic salt, such as NaCl, instead of detergent, then no foam is formed. Foam formation indicates that the surface-active agent adsorbs at the surface, and forms a TLF (consisting of two layers of amphiphile molecules and some water). This has led to many theoretical analyses of surfactant concentration (in the bulk phase) and surface tension (consequent on the presence of surfactant molecules at the surface). The thermodynamics of surface adsorption has been extensively described by the Gibbs adsorption theory (Chattoraj and Birdi, 1984). 

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