Helmholtz free energy functional (Λ[{pα}]) as
^[{O] = ^-Keat(r) Vtt = l,m, (5.8)
where μa is chemical potential of the segment a, and V^xt is the external field acting
onto it. Solution of the set of these (Euler-Lagrange) equations gives the equilibrium
density profile of the segments. To derive the Helmholtz free energy, the copolymer
chain molecule is considered as the limit of complete association of a mixture of
associating atomic molecules (or associating segments), with off-centered association
sites. The Helmholtz free energy functional of such a mixture of associating segments
can be written as
A[{pα}] = + AEX,hs [{pα}] + AEX,chain[{pa}] + AEX,att[{pa}], (5.9)
where Ald is the ideal free energy of the segments, AEX,hs is the excess free energy
due to the excluded volume of the segments (hard sphere repulsions), AEX'cham is
the excess free energy due to chain formation in the limit of complete association of
the segments, and Aex,m is the excess free energy due to the long range attractions
between the segments.
The individual free energies and their functional derivatives were derived in chap-
ter 4. Here, the final equilibrium density profile of the segments and grand free energy
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