Chitosan-stabilized emulsion gels via pH-induced droplet flocculation

Abstract

The formation and stabilization of Pickering-type emulsion gels at low oil fractions (φ) remains a challenge. This work reports on the fabrication of emulsion gels solely stabilized by chitosan at φ values as low as 0.2 via pH adjustment and storage time. We show that slight adjustments in pH in a narrow window from 6.4 to 7.0 (near the pKa of chitosan) can effectively tune the gelation properties of chitosan through control of surface charge and floc size. Upon storage of 2 or more days, oil droplets coated with these aggregated chitosan particles flocculate to form and strengthen self-supporting emulsion gels. The increase in pH not only promotes the formation of networked chitosan particles in the continuous phase but also leads to an increase in inter-droplet interactions, resulting in an enhancement in emulsion gel strength. Increasing φ from 0.2 to 0.75 results in more rapid emulsion gel formation with a higher elastic modulus. The present findings demonstrate the effectiveness of pH-tailored chitosan particles in generating and stabilizing O/W emulsion gels with tunable microstructure and rheological properties.