external field ( Verrt(R)) can be related to the intrinsic Helmholtz free energy as
m p
Ω[{ft,(r)}] = Λ[{ftk(r)}] - ∑ / ⅛H⅛ - ŋr')), (4.1)
α=l -ʃ
where pa is the density of the ath segment, μa is its chemical potential, and Va is
the external field acting on that segment. Minimization of the grand potential with
respect to density of the segments yield a system of variational equations, known as
the Euler-Lagrange equations,
H{fe(r)}] = _ yext^ V a = l,m, (4.2)
^pOt (r )
Solution of this set of equations gives the equilibrium density profile of the segments.
From the equilibrium density profiles, both structural and thermodynamic properties
can be calculated following the standard statistical mechanical relations. The intrinsic
Helmholtz free energy functional of such a chain of ‘m’ segments is obtained along
similar lines as iSAFT [60]. Considering the polyatomic system as a mixture of
associating spherical segments in the limit of complete association, the free energy
functional can be derived from Wertheim’s TPTl [46, 47, 58, 26, 27, 28, 29, 62]. The
model considers spherical segments with hard cores and highly directional attraction
sites. For a linear chain of m segments, consider an m component stoichiometric
mixture of associating spheres. Component 1 has a single association site labeled ‘A’,
components 2 till (m-l) have two association sites labeled ‘A’ and ‘B’ while component
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