is obtained, and the predictions are in better agreement with experimental data for
asymmetric mixtures of n-alkanes than PC-SAFT. The next section of this chapter
provides a detailed description of SAFT-D. The results obtained for the homologous
series of n-alkanes, long chain alkanes, and polymers are discussed in the subsequent
section. SAFT-D predictions are compared with results obtained from the PC-SAFT
model for both monodisperse and polydisperse polymer solutions.
2.2 SAFT-D equation of state
Consider a mixture of chain fluids such that the chain fluid of type T has imi,
number of segments, σl is the size of their segments (i.e. homonuclear polymer chains),
and xi is their (number) fraction in the mixture. For total ‘N’ number of chains in
the mixture, the Helmholtz free energy is given in terms of a perturbation expansion
as
I дспаяп i дагзр
A = Aid + Afes
(2.1)
where, Ald is the ideal free energy of segments, and the various excess contributions
to the free energy are: Ahs due to volume exclusion∕repulsive interactions, Acham
due to chain formation, and Adτsp due to the dispersive∕attractive interactions. It is
clear from eqn. 2.1 that there are two perturbations involved. First one (chain term)
derives the free energy of hard-chain fluid using perturbation from a reference fluid
of hard spheres in case of SAFT-HS and hard dimers in case of SAFT-D, while the
second one (dispersion term) derives the free energy of the attractive chain fluid using
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