Solubility parameter concept assumptions

There have been many attempts to divide the overall solubility parameter into components corresponding to the several intermolecular forces. For example, a so-called three-dimensional solubility parameter concept is built on the assumption that the ced is an additive function of contributions from dispersion (d), polar (p), and H-bonding (h) forces. It follows that... 

In examining the reasons for the fundamental use of the solubility parameter concept, it must be recognized that independent of any assumptions in the derivation of Equation 1 and the definition of 6 in Equation 2 there is a computational and experimental problem. This problem is often overlooked. Consider mixing two components, each having molar volumes of 100 cm /mol and energies of vaporization of 8000 and 9000 cal/mol. From Equations 1 and 2, AE would be computed as 13.6 cal/mol. If AE for the first component is in error by only 5%, so that AE is 7600 cal/mol instead of 8000 cal/mol, the computed value of AEjq will be 19.2 cal/mol, almost 50% higher than the earlier value of 13.6 cal/mol. Yet it is rare indeed that AE is known to within 5%. Table II, compiled by... 

For chromatographic applications, the most useful models of solvent properties are the solubility parameter concept, Snyder s solvent strength and selectivity parameters, solvatochromic parameters and the system constants of the solvation parameter model for gas to liquid transfer. The Hildebrand solubility parameter, 8h (total solubility parameter), is a rough measure of solvent strength, and is easily caleulated from the physical properties of the pure solvent. It is equivalent to the square root of the solvent vaporization energy divided by its molar volume. The original solubility parameter concept was developed from assumptions of regular solution behavior in which the principal intermolecular interactions were dominated by dispersion forces. 

For nonionic surfactants, an optimization of the process was achieved by using a similar approach to the so-called Cohesive Energy Ratio (CER) concept developed by Beerbower and Hill for the stability of classical emulsions (H). Its basic assumption is that the partial solubility parameters of oil and emulsifier lipophilic tail and of water and hydrophilic head are perfectly matched. Thus, the Vinsor cohesive energy ratio Ro, which determines the nature and the stability of an emulsion, is directly related to the emulsifier HliB (hydrophile-lipophile balance) by... 

The concept of the solubility parameter originates from Hildebrand s work on enthalpy of regular solutions [Shinoda, 1978]. Accordingly, in a strict sense, the molecular interactions should be nonspecific, without forming associations or orientation, hence not of the hydrogen or polar type. Another fundamental assumption was that the intermolecular interactions 1-2, are geometric mean of the intramolecular interactions, 1-1 and 2-2 ... 

Thermodynamic analysis allows solutions to be classified after thermodynamic parameters have been determined. It cannot, however, predict the solubility or miscibility of two substances without the aid of additional assumptions. A prediction of this type is possible with the concept of the solubility parameter, which is based on the following considerations. 

---