https://doi.org/10.1351/goldbook.ST07466
Parameter used in predicting the solubility of non-electrolytes (including polymers) in a given solvent.
For a substance \(\ce{B}\), \[\delta_{\ce{B}} = \left (\frac{\Delta_{\rm{vap}}E_{\rm{m,B}}}{V_{\rm{m,B}}} \right)^{1/2}\] where \(\Delta _{\rm{vap}}E_{\rm{m,B}}\) is the molar energy of vaporization at zero pressure and \(V_{\rm{m,B}}\) is the molar volume.
For a substance \(\ce{B}\), \[\delta_{\ce{B}} = \left (\frac{\Delta_{\rm{vap}}E_{\rm{m,B}}}{V_{\rm{m,B}}} \right)^{1/2}\] where \(\Delta _{\rm{vap}}E_{\rm{m,B}}\) is the molar energy of vaporization at zero pressure and \(V_{\rm{m,B}}\) is the molar volume.
Notes:
- 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.
- 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.
- The SI units are \(\pu{Pa^{1/2}} = \pu{J^{1/2} m^{-3/2}}\), but units used frequently are \((\pu{\upmu Pa})^{1/2} = (\pu{J cm-3})^{1/2}\) or \((\pu{cal cm-3})^{1/2}\), where \(\pu{1}\ \pu{(J cm-3)^{1/2}} \approx \pu{2.045}\ \pu{(cal cm-3)^{1/2}}\). The unit calorie is discouraged as obsolete.