Effect of surface charge density of bacterial cellulose nanofibrils on the rheology property of O/W Pickering emulsions

Abstract

In this study, the effect of surface charge density of bacterial cellulose nanofibrils (BCNF) on the rheological characteristics of O/W Pickering emulsions was investigated by regulating the fibril charge density. BCNFs with different carboxylate group contents (0.66, 0.90 and 1.16 mmol/g dry cellulose, representing as TOBC-a, -b, and -c) were obtained by 2,2,6,6-tetramethylpiperidine-nitrogen-oxide (TEMPO) oxidation. These oxidized products were used as Pickering stabilizers to prepare O/W Pickering emulsions. Diffusing wave spectroscopy (DWS)-based microrheology was utilized to reflect the rheological features of emulsions. TOBC-a stabilized emulsion had a lower macroscopic viscosity, lower elasticity, and better fluidity. It was because a weaker fiber network was formed in the continuous phase during the ultrasonication emulsification. The influences of pH and ionic strength on the rheological properties of high-charged TOBC-c stabilized emulsions were also investigated. The emulsion prepared at pH 3.0 exhibited the highest viscosity. It was probably because the inter-fibrils electrostatic repulsion was weakened by the addition of HCl, and the hydrogen bonding interaction became dominant due to the protonation of carbohydrate group. At pH 11, the emulsion viscosity was lowest, which was resulted from the destruction of the intra-fibrils hydrogen bonds. With the NaCl concentration increased, the emulsion viscosity and elasticity increased. It was induced by the fact that the charge shielding effect of NaCl facilitated the formation of a tighter fibrils network in the continuous phase. These results have the potential to provide a guide for developing emulsion-based products with appropriate fluidity to broaden the practical application of emulsion.