The name is absent

of mixing is obtained by counting the number of all the possible configurations of
the polymer-solvent system on the lattice, while the enthalpy of mixing is obtained
by accounting for all the nearest neighbors’ interactions, with χ being the interac-
tion parameter. The entropy of mixing is always positive and thus always favors
mixing, however it is small for large polymer molecules. For certain values of χ corre-
sponding to unfavorable interactions between the polymer and solvent molecules, the
enthalpy of mixing becomes sufficiently positive, and the system exhibits liquid-liquid
(L-L) immiscibility characterized by a upper critical solution temperature (UCST).
Another interesting liquid-liquid immiscibility is commonly observed in polymer sys-
tems, where the single liquid phase becomes unstable on increasing the temperature
in the direction of the critical point of the solvent. The lowest temperature at which
the two-phase (L-L) region appears is referred to as the lower critical solution tem-
perature (LCST). LCST behavior occurs in polymer solutions due to the difference
in free volume or compressibility of the polymer and solvent molecules [11, 12, 13].
Consequently, Flory-Huggins theory, which assumes incompressibility, cannot predict
the LCST behavior in polymer solutions. Phenomenological approaches have been
introduced to describe polymer solutions with a LCST in Flory-Huggins approach
by defining an empirical temperature, composition, and even pressure dependence on
the χ parameter [14, 15, 16, 17, 18].

Other more fundamental approaches, such as the lattice cell models and lattice
hole models, aim to incorporate compressibility in the lattice model. In lattice cell

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