Mixtures of Rods and Random Coils

Application of the lattice scheme to a system consisting of rodlike molecules, random coils and a solvent is straightforward The free energy of the nematic phase would be increased markedly by the presence of a substantial proportion of the random coil. 

The latter component consequently is predicted to be virtually excluded from this phase. This striking deduction from theory follows solely from the steric requirements of the two kinds of macromolecules no other interactions between them are required. 

Aharoni has reported experiments on the system tetrachloroethane/polyiso-cyanate (POIC)/polystyrene that confirm the foregoing predictions. The nematic phase separates at compositions in the range predicted polystyrene does not occur in detectable quantities in this phase. The binodal for the isotropic phase resembles the calculated curve shown in Fig. 6. 

Recently Hwang, Wiff and Benner have determined the phase diagram for the ternary system methanesulfonic acid/poly(phenylene benzothiazole) (PBT)/poly- 

Reflecting on the unique features for these ternary systems, we observe that, in rejecting the random coil, the nematic phase manifests a principal characteristic of crystals in general, thus validating the term liquid crystal . It will be apparent, however, that the presence of the random coil in the system affects the composition of the anisotropic phase substantially, its absence therein notwithstanding. This is a consequence of the abundance of random coiled component in the coexisting isotropic phase it markedly increases the chemical potential of the rodlike component in that phase and, concomitantly, decreases the chemical potential of the diluent. The concentration of the rodlike component in the anisotropic phase consequently is caused to increase. 

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