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Hoy Solubility Parameter Calculation - Theory

The Hoy Solubility Parameter method (ref.) is one of the best and the fastest methods to predict whether an organic material is compatible with another (or soluble in) organic material (solvent, polymer, ...).

Theory
The Hoy application
Features and screenshots
Pricing

The method is essentially a group contribution method: for each chemical group in the molecule, contributions are added to the total. The Hoy Solubility Parameter method is special as it allows to "correct" for structural features like: cis, trans (around double bonds), ortho-, meta-, para-substitution (aromatics), branching (isopropyl, t-butyl, conjugation of double bonds, and rings.

The Hoy method for the prediction of the Solubility Parameter is based on three different contributions:

  • A dispersive contribution (δD): i.e. all non-polar contributions
  • A Polar contribution (δP): polar contributions
  • A hydrogen bond contribution (δH): only present when the molecule can form hydrogen bonds
Each of this can be regarded as a vector in three-dimensional space, so the total solubility parameter(δ(tot.)) is defined by:
δ(tot.)2 = δD2 + δP2 + δH2

The solubility parameter of a material can thus also be regarded as a point in 3-dimensional space.

When predicting the compability of two organic materials (say A and B), the distance in 3-dimensional space between the components is calculated:

D(A-B)2 = [δD(A) - δD(B)]2 + [δP(A) - δP(B)]2 + [δH(A) - δH(B)]2

The smaller the distance between two components, the more compatible they are.

For those interested in a more extensive theoretical and practical background: John Burke has written an excellent overview on the theory and applications of Solubility Parameters.

Remark that the Solubility Parameter of a material can also be determined experimentally from its heat of vaporization.

References:

  • K.L.Hoy, New values of the solubility parameters from vapor pressure data, J.Paint Techn., Vol.42, Nr.541, p.76 (1970).
  • K.L.Hoy, The Hoy tables of solubilty parameters, Union Carbide Corp., 1985
  • K.L.Hoy, Solubility Parameters as a design parameter for water borne polymers and coatings. Preprints 14th Int.Conf. Athene, 1988.
  • K.L.Hoy, J.Coated Fabrics, 19, p.53 (1989)

Jos Aerts, Computer Chemistry Consultancy, April 2002