The cavitation forces

Another important contribution related to non-electrostatic terms is the cavitation. This is related to the work to create a macroscopic cavity in the bulk of liquid. This term is proportional to the surface tension y and the surface 

For the evaluation of there are several formulas based on the shape and size of the solute and on different parameters of the solvent surface tension [43], surface tension with macroscopic correction [44], isothermal compressibility [45] and geometrical parameters of the solvent molecules [46]. The first three techniques follow the same philosophy. They do not rely on a detailed description of the discrete solvent and make use of experimental bulk parameters of the solvent, in analogy with the dielectric constant of the electrostatic continuum model. As an example of this kind of approach we present Sinanoglu s formula [44] 

The forth approximation which has been developed by Pierotti [46] is quite different. The basic formula is derived from the theory of discrete model of fluids (the scaled particle theory) [47] 

The coefficients AT, are expressed in terms of some of the properties of solvent (molecular radius, numeral density) and solution (pressure, temperature). The main reason why the very different formulas for the calculations of AG av exist is because the cavitation energy is not observable and an evaluation of the merits of an expression for AG av cannot rely on direct comparisons with thermodynamic data. It is believed [21] that Pierotti s formula works fairly well for solvents of small size, even when they are polar, protic, or hydrogen bonded (for example, methanol and water). 

Finally we would like to mention the simple parametric relationship of Cramer and Truhlar [48] that includes the dispersion and cavitation term together 

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The continuum models presented in previous sections are focused only on electrostatic effect which is accompanied by insertion of a solute in a solvent, namely the bulk polarization of the solvent by the field of the solute. However, all these models neglect some other physical effects [36]. Among them probably the most important are the dispersion and the cavitation forces. 

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