High internal phase emulsions stabilized solely by carboxymethyl chitosan

The ability of carboxymethyl chitosan (CMCS) to stabilize high internal phase emulsions (HIPEs) was investigated under various conditions. Emulsions with optimal properties (ultra-high stability, good gelation, and high plasticity) were obtained using single-step shear dispersion at a CMCS content of 0.3 wt% and near-neutral pH. CMCS functioned as a "structuring agent" to form three layers of jammed networks that immobilized the oil droplets enmeshed therein, through molecular rearrangement and characteristics such as flexible molecular entanglement chains and film-forming properties. Specifically, the hierarchical structures from the innermost layer (closest to the droplets) to the outermost layer were interfacial film, branching linear/membrane structures, and outer non-interfacial membranes, respectively. The outer layers of reticular membranes (without adhering onto the droplets) improved the emulsion's bulk viscosity and steric hindrance and further pushed the first layer closer to the dispersed droplets to create more compact adsorption, stabilize a large interfacial area, and improve the protective coating. The branched structure of CMCS also enabled bridging and, hence, the tight interconnection of oil droplets. Overall, the synergistic effects of various factors allowed CMCS to effectively stabilize HIPEs. The adopted strategy is expected to facilitate the development of other emulsifiers for HIPEs.