Gibbs Equation on the Relationship between Interfacial Tension and Adsorption

2 Gibbs Equation on the Relationship between Interfacial Tension and Adsorption 

Molecules in the surface or interfacial region are subject to attractive forces from adjacent molecules, which result in an attraction into the bulk phase. The attraction tends to reduce the number of molecules in the surface region (increase in inter-molecular distance). Hence work must be done to bring molecules from the interior to the interface. The minimum work required to create a differential increment in surface dA is ydA, where A is the interfacial area and y is the surface tension or interfacial tension. One also refers to y as the interfacial Gibbs free energy for the condition of constant temperature, T, pression, P, and composition (n = number of moles) 

In water the intermolecular interactions which produce surface tension are essentially composed of 114 

It is estimated that about one third of the interfacial tension is due to Van der Waals attraction, and the remainder is due to hydrogen bonding. 

The interfacial tension between two phases is subject to the resultant force field made up of components arising from attractive forces in the bulk of each phase and the forces, usually the London dispersion forces, operating accross the interface itself (Fowkes, 1965 Adamson 1990) (see Appendix, this Chapter). 

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