Flory-Huggins theory tends to agree well with experiments in the semi-dilute concentration regime and can be used to fit data for even more complicated blends with higher concentrations. The theory qualitatively predicts phase separation, the tendency for high molecular weight species to be immiscible, the χ χ ∝ ∝ T − − 1 interaction-temperature dependence and other features commonly observed in polymer mixtures. However, unmodified Flory-Huggins theory fails to predict the lower critical solution temperature observed in some polymer blends and the lack of dependence of the critical temperature T c on chain length r i . Additionally, it can be shown that for a binary blend of polymer species with equal chain lengths ( N A = N B ) the critical concentration should be ψ ψ c = 1 / 2 ; however, polymers blends have been observed where this parameter is highly asymmetric. In certain blends, mixing entropy can dominate over monomer interaction. By adopting the mean-field approximation, χ χ parameter complex dependence on temperature, blend composition, and chain length was discarded. Specifically, interactions beyond the nearest neighbor may be highly relevant to the behavior of the blend and the distribution of polymer segments is not necessarily uniform, so certain lattice sites may experience interaction energies disparate from that approximated by the mean-field theory.