ABSTRACT
By definition, the enthalpy of mixing of regular solutions is independent of temperature, and for mixtures of hydrocarbons i and j the temperature dependence of the enthalpy of mxing is in fact observed to be small; in terms of Hildebrand parameters this corresponds to iδ and jδ having similar temperature dependences. It follows from its definition that the Hildebrand parameter decreases with increasing temperature, and to a good approximation over a moderate temperature range for the simpler, nonpolar liquids dlnd/dT=-k. However, it should be noted that the effect on cohesion parameters of changing temperature can be utilized to provide a cohesion parameter spectrum and also that there are other cases, particularly in liquid/vapor situations where the temperature dependence of δ values is even more important. Values of cohesion parameters at higher temperatures are now becoming available from gas chromatographic studies exemplified by the Hansen parameters at 80°C of the alkyl derivatives of phenol and resorcinol.
