δd | the dispersion contribution to δ |
δp | the polar contribution to δ |
δh | the hydrogen bonding contribution to δ |
The relation δ2=δd2+δp2+δh2 holds. Thus for non-polar solvents δp=δh=0 and δd=δ.
Solutes do also have δd,δp and δh parameters and an additional parameter, the interaction radius, R0. To determine the solubility of a compound the distance Ra is calculated.
Ra2= 4×Δδd2+ Δδp2+ Δδh2 |
where |
Δδd2= (δsolute,d-δsolvent,d)2 |
Δδp2= (δsolute,p-δsolvent,p)2 |
Δδh2= (δsolute,h-δsolvent,h)2 |
For a more detailed discussion see →The Official Hansen Solubility Parameter Site or →Solubility Parameters: Theory and Application
The parameters here are given in (cal/mL)½ in order to be consistent with Hildebrand δ. To convert to MPa½ multiply by 2.05.