Gelation of κ-carrageenan in water-in-water emulsions.

The gelation behaviour of κ-carrageenan (κ-car) in the presence of KCl was examined in binary mixtures with dextran (Dex) or polyethylene oxide (PEO), as well as in water-in-water (W/W) emulsions formed by these polymers. The results show that the presence of Dex or PEO has only a weak effect on κ-car gelation. However, it affects the microstructure rendering the κ-car network more homogenous with increasing viscosity of the DEX or PEO solutions. In the W/W emulsions, κ-car preferentially partitioned to the Dex-rich phase. Rheological measurements showed that the storage modulus (G') increased with the volume fraction of the PEO phase (φ) as long as the Dex phase was continuous. The transition of the DEX phase from continuous to dispersed at φ ≈ 70 % resulted in a sharp reduction of the gel stiffness. Weak gels were nevertheless formed up to φ ≈ 80 % due to aggregation of gelled Dex droplets into a system spanning network. For φ > 90 %, G' increased again sharply as an increasing fraction of the κ-car partitioned to the PEO phase. This work highlights that the rheology of W/W emulsions can be tuned by adding κ-car.