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-carrageenan was further examined by macroscopic observations and by NMR. A state diagram, which is the equivalent of a phase diagram but including also nonequilibrium states (in our case a gel), was established in the mixed salt solutions of NaI/CsI where the competition between phase separation and gelation could be studied. The phase boundaries of the nematic phase depended on molecular weight and ionic strength qualitatively 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 content was larger in the nematic than in the isotropic phase.

Nyckelord

NEMATIC PHASE-TRANSITION

SELECTIVE SITE BINDING

HELIX-COIL TRANSITIONS

BOLTZMANN CELL MODEL

IOTA-CARRAGEENAN

GELS

CONFORMATION

SUSPENSIONS

MIXTURES

POLYMERS

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