The objective of the current work is to extend iSAFT to satisfy stoichiometry
and to demonstrate the applicability of modified iSAFT to heteronuclear chains by
applying it to various model systems. The next section presents the theoretical devel-
opment of modified iSAFT. The theory satisfies the overall stoichiometry, and each
segment knows about all the other segments in the chain. Furthermore, the theory
requires only the bulk chemical potential of the chain as an input rather than seg-
ment bulk chemical potentials in the case of the original iSAFT. However the theory
is computationally more expensive than original iSAFT. The theory has been success-
fully applied to study complex systems like lipids near a surface, lipid bilayers, thin
and ultra-thin copolymer films, and ordering in bulk copolymer melts. The results
for these systems and their comparisons with results from molecular simulations are
discussed in the subsequent section.
4.2 Model and theory
Consider a fluid mixture of polyatomic molecules where the molecules consist of
spherical segments tangentially bonded together to form flexible chains. Each of the
segments of the chains can be different. For the sake of simplicity, the derivation is
presented for a pure fluid of chain molecules with 1m, segments, but the theory is in
general applicable to mixtures.
The grand free energy of a chain of ‘m’ segments at fixed V, T, and μ in an
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