Excess isobaric thermal expansion in the systems formed by oligooxaethylene and alkane in terms of an associated mixture model with equation of state contribution

The concept of self-association oligooxaethylenes (glymes) is discussed in terms of the associated mixture model with equation of state contributions [A.J. Treszczanowicz, G.C. Benson, Fluid Phase Equilib., 23 (1985) 117]. The model was applied to interpret and describe the excess thermodynamic properties of binary mixtures formed by 2,5-dioxahexane or 2,5,8-trioxanonane with n-alkane. The excesses enthalpy HE, heat capacity CpE, volume VE and isobaric thermal expansion ApE=(∂VE/∂T)p were used to estimate the model parameters: standard enthalpy, entropy and volume of self-association and non-specific interactions parameter. The application of the equation of state alone does not allow to describe ApE and other thermodynamic properties, unless association is taken into consideration. Calculations show the glymes to be very weakly self-associated, and characterized by the high monomer concentration in the pure state. The description of the glyme+alkane mixtures was compared with the results for relatively strong self-associated 1-alkanol mixtures. The chemical contributions to ApE and CpE for glyme mixtures have negative signs, different than those for alkanol mixtures. The association, even if it is weak, has an essential contribution to the thermodynamic properties.