Abstract
N.m.r. and rheological measurements have been used to study the gelation of iota carrageenan. Gelation has been found to occur only at polymer concentrations above the critical entanglement concentration. The high temperature sol state above the gel-sol transition appears to be an entangled polymer network. Although Li + and Na + ions are less effective at gelling the polymer than K +, Rb + and Cs + all cationic forms studied gel at sufficiently high polymer concentration and ionic strength. 7Li +, 23Na, 39K, 87Rb and 133Cs n.m.r. studies have been made as a function of temperature. The lithium salt form (2.2% w/w concentration) formed a viscoelastic solution at room temperature. The other salt forms gelled on cooling. The spectra of Li, Na and Cs carrageenan showed little change on heating whereas K and Rb spectra showed marked changes in apparent intensity. The nature of the cation interaction with the juntion zones is discussed.
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