Effect of soft interaction between molecules

Later Flory further took the two soft interactions between the molecules into account. The anisotropic interaction is associated with molecular orientations while the isotropic one is irrelevant of the molecular orientation. In fact, the anisotropic interaction was the basis of another well-known theory in liquid crystals — Maier-Saupe theory (Maier Saupe, 1959). Flory successfully captured the essence of the theory. 

First we introduce the isotropic interaction which results from the mixing of rods and solvents. The previous theory, without the mixing contribution to entropy, is only applicable to an athermal system. If there is a mixing entropy contribution, the free energy in Equation 2.39 is implemented by a term x4 ns, where x is the Flory-Huggins interaction parameter. Flory called the mixing term the isotropic soft interaction to distinguish it from the steric interaction of rods. 

At the coexistence of the two phases the chemical potentials of the rods and solvents in both the liquid crystals phase and isotropic phase must be equal and thus the following set of equations for f , // and y holds 

Warner and Flory (1980) found that the introduction of the anisotropic attractive force predicts this effect. This anisotropic interaction associated with molecular orientation is expressed by 

---