Liquid-crystalline ordering in solutions of polyelectrolytes

The isotropic-nematic phase transition in solutions of stiff-chain polyelectrolytes is considered on the basis of the Onsager approach for the limiting cases of charged rods and persistent macrolecules. We plotted a full family of phase diagrams for orientational transitions in solutions of polyelectrolytes with any charge density as a function of the low-molecular-weight salt concentration. It is shown that charging of macromolecules can lead not only to the renormalization of the chain diameter (discussed by Onsager) or to the twisting effect (predicted by Odijk et al.), but in some cases also to a variety of other regimes, including transitions with very narrow phase separation regions, or with a second orientational transition to a highly oriented nematic phase upon the increase of polymer concentration.