LIQUID CRYSTALLINITY VERSUS GELATION OF KAPPA-CARRAGEENAN IN MIXED SALTS - EFFECTS OF MOLECULAR-WEIGHT, SALT COMPOSITION, AND IONIC-STRENGTH

The recently discovered isotropic/nematic phase transition in kappa-ca rrageenan was further examined by macroscopic observations and by NMR. A state diagram, which is the equivalent of a phase diagram but inclu ding also nonequilibrium states (in our case a gel), was established i n the mixed salt solutions of NaI/CsI where the competition between ph ase separation and gelation could be studied. The phase boundaries of the nematic phase depended on molecular weight and ionic strength qual itatively as expected for a charged rigid polymer. From these data the persistence length of the kappa-carrageenan helix was estimated as 60 -90 nm. The volume fraction of the nematic phase depended sensitively on the overall helical content. In coexisting phases, the helical cont ent was larger in the nematic than in the isotropic phase.