solubility parameter, δ

Parameter used in predicting the solubility of non-electrolytes (including polymers) in a given solvent.
For a substance B,
δ B = ( Δ vap E m , B V m , B ) 1/2
where Δ vap E m , B is the molar energy of vaporization at zero pressure and V m , B is the molar volume.
  1. For a substance of low molecular weight, the value of the solubility parameter can be estimated most reliably from the enthalpy of vaporization and the molar volume.
  2. The solubility of a substance B can be related to the square of the difference between the solubility parameters for supercooled liquid B and solvent at a given temperature, with appropriate allowances for entropy of mixing. Thus, a value can be estimated from the solubility of the solid in a series of solvents of known solubility parameter. For a polymer, it is usually taken to be the value of the solubility parameter of the solvent producing the solution with maximum intrinsic viscosity or maximum swelling of a network of the polymer. See J.H. Hildebrand, R.L.Scott, The Solubility of Nonelectrolytes, 3rd ed., Reinhold Publishing (1950); Dover Publications (1964), Chap. VII, p.129; Chap. XXIII, for the original definition, theory, and extensive examples.
  3. The SI units are Pa 1/2 = J 1/2 m −3/2, but units used frequently are µPa 1/2 = ( J cm −3 ) 1/2 or ( cal cm −3 ) 1/2, where 1 ( J cm −3 ) 1/2 ≈ 2.045 ( cal cm −3 ) 1/2. The unit calorie is discouraged as obsolete.
PAC, 2008, 80, 233 (Glossary of terms related to solubility (IUPAC Recommendations 2008)) on page 264