CO₂ responsive self-standing Pickering emulsion gel stabilized with rosin-based surfactant modified cellulose...

Emulsion gel was developed to provide desirable texture, palatability and functionality to food products. Tunable stability of emulsions is often desired, as in certain situations, the chemical content release usually relies on emulsion induced destabilization of the droplet. However, the destabilization for emulsion gel is difficult because of the formation of highly entangled networks. To address this issue, a fully biobased Pickering emulsion gel stabilized by cellulose nanofibrils (CNF) modified with a CO₂ responsive rosin-based surfactant, maleopimaric acid glycidyl methacrylate ester 3-dimethylaminopropylamine imide (MPAGN) was reported. The emulsification/de-emulsification can be reversibly regulated because this surfactant has sensitive CO₂ responsive property. MPAGN can be reversibly between active cationic (MPAGNH⁺) and inactive nonionic (MPAGN) responsive to CO₂ and N_2. The microstructure of the emulsion gel was observed and compared before and after the response. The rheological properties of emulsion gel stabilized by different concentrations of MPAGNH⁺ and different contents of CNF were studied separately. As 0.2 wt% CNF was dispersed in 1 mM MPAGNH⁺ solution, the obtained emulsion can be self-standing for long duration. The rheology study indicated that these emulsions show typical gel characteristics with shear-thinning behavior. The stabilization mechanism of these gel emulsion is a synergistic effect caused by the combination of CO₂ responsive Pickering emulsion and intertwined network caused by the hydrogen-bond interaction among CNF.