(Invited) Phase Separation in Mixed Polysaccharide Gels

Abstract

Phase separation behavior has been studied for the mixed polysaccharides of kappa carrageenan (k-carr) and iota carrageenan (i-carr). Temperature dependence of G’ and G” for the mixture solution measured by dynamic rheological measurement showed two step increases in cooling process, suggesting the individual network formation of k-carr chain and i-carr chain at gelling temperatures (Tg) corresponding to Tg for pure each solution of k-carr and i-carr. The particle tracking method using fluorescent particles with diameter of 100nm was carried out for the mixtures indicating the formation of phase separated structure in the mixture. It was also indicated that the local viscosity of k-carr rich phase was lower than that of pure k-carr solution with the same concentration and the local viscosity of i-carr rich phase was higher than that of pure i-carr solution, suggesting that each phase contions other carrageenan chain. The large amplitude oscillatory shear (LAOS) measurements for the mixtures with various mixing ratios were also measured to investigate the effect of the phase separated structures on the physical property. The response of strain against the large deformation showed characteristic behaviors corresponding to the change of mixing ratio, suggesting a transitional change of phase separation structure with the change of volume ratio of each phase.