Carrageenans are polysaccharides used in food and biotechnological applications. In our study, we focus on three types of carrageenans, κ-(KC), ι-(IC), and λ-(LC) carrageenans with different numbers and positions of sulfate groups. By decreasing temperature, carrageenan aqueous solutions become gels in which carrageenan chains are cross-linked by aggregated domains of helical chains (Fig. 1). We investigated the hierarchical structure of the carrageenan gels by SANS to understand the microscopic origin of their mechanical properties [1].

Figure 2 shows the temperature dependence of elastic modulus $G^{\prime}$ and loss modulus $G^{\prime\prime}$ of KC, IC, and their mixtures, KCIC gels. For KC and IC gels, $G^{\prime}$ increases drastically at a certain temperature, where sol-gel transition occurs. $G^{\prime}$ of KC gel is larger than that of IC gel, indicating that KC gel is stiffer than IC gel. KCIC gel exhibits a two-step increase of $G^{\prime}$, corresponding to independent aggregation of KC and IC chains in KCIC gel.

To study the microscopic structure of KC, IC and KCIC gels, we performed SANS measurements at SANS-U. The SANS profiles are converted to Kratky plots in Fig. 3. In the Kratky plots, a peak was observed at 0.06 Å^-1 for KC gel, 0.07 Å^-1 for KCIC gel, and 0.09 Å^-1 for IC gel, respectively. This suggests that the chain aggregate in KC gel is larger than that in IC gel, which results in the higher elastic modulus of KC gel.

References

• [1] L. Geonzon, K. Hashimoto, T. Oda, S. Matsukawa and K. Mayumi, Macromolecules, 56, 8676 (2023).

Authors

• K. Mayumi, and L. C. Geonzon