ISOTROPIC LIQUID-CRYSTAL PHASE-EQUILIBRIUM IN SEMIFLEXIBLE POLYMER-SOLUTIONS - EFFECTS OF MOLECULAR-WEIGHT AND IONIC-STRENGTH IN POLYELECTROLYTE SOLUTIONS

The isotropic-liquid crystal (cholesteric) phase boundary concentrations for aqueous solutions of xanthan, an ionic double-helical polysaccharide, were determined as functions of the molecular weight of xanthan and the added sodium chloride concentration. The phase boundary concentrations increased sharply with decreasing molecular weight at low molecular weights, as in the case of neutral stiff polymer solutions, and depended strongly on the added salt concentration. The latter dependence demonstrates the importance of the electrostatic interaction between polymers in the isotropic-liquid crystal phase equilibrium. These experimental results were compared with two theories: the Onsager theory extended by Odijk to semiflexible polyelectrolyte solutions and a perturbation theory proposed by us (Sato, T.; Teramoto, A. Physica A 1991, 176, 72). The latter theory succeeded in almost quantitative prediction of the experimental phase boundary concentrations for xanthan. The same comparison was performed on two other rigid polyion systems: tobacco mosaic virus and DNA.