Rheological properties of concentrated solutions of fucoidan in water and in an ionic liquid

Dynamic viscoelasticity has been examined for concentrated solutions of fucoidan from Cladosiphon okamuranus in water and in an ionic liquid 1-butyl-3-methylimidazolium acetate (BmimAc). The existence of the electrostatic interaction between fucoidan chains in the aqueous solutions and its disappearance in the BmimAc solutions have been clearly shown by the difference in the terminal flow behavior between the aqueous and BmimAc solutions. On the other hand, the rubbery plateau indicating the entanglement coupling between fucoidan chains has been observed for both solvents at rather high concentrations. The molecular weight between entanglements (M-e) for fucoidan in the BmimAc solutions has been determined from the plateau modulus at several concentrations and then M-e for fucoidan in the molten state (M-e,M-melt) has been estimated to be 1.0 x 10(4) as a measure of the specific chain characteristics of fucoidan.