Cellulose nanocrystals (CNC) Pickering emulsions (PEs): Rheological aspects and stability of low-to-medium internal...

Given the importance of the rheological properties of Pickering emulsions (PEs) in their stability and practical applications, CNCs were utilized to prepare low-internal-phase (LIPE) and medium-internal-phase (MIPE) Pickering emulsions. LIPEs with 5 % and 10 % oil showed phase separation during storage. They remained stable under centrifuge stress. MIPE with 50 % oil was unstable under centrifugation. LIPEs with 5 % and 10 % oil concentrations had smaller droplets than MIPE. All PEs exhibited G' > G″, more pronounced in MIPE. The strain at the crossover point decreased from 120.8 ± 0.01 % to 39 ± 0.8 % for 5 % and 50 % oil content, respectively, while the stress increased from 1.6 ± 0.9 Pa to 15 ± 3 Pa. Their frequency-sweep tests showed G' > G″. LIPEs displayed fluid-like and solid-like behavior at low and high frequencies, respectively. MIPE showed no frequency dependency. All PEs exhibited pseudoplastic behavior (Carreau model). MIPE displayed higher viscosity at shear rate = 0 than LIPEs. The hysteresis area indicated thixotropic behavior, suggesting time-dependent structural relaxation in all PEs. In conclusion, at 3 % wt. of CNC, increasing φ up to 50 % resulted in a more gel-like and viscoelastic structure with high storage stability and relatively stress-susceptible properties. Therefore, LIPE (20 % φ) and MIPE can be successfully utilized in specific food and cosmetic product formulations.