Size effect of carboxymethyl chitin nanocrystals on Pickering foam and emulsion in aqueous solution

Abstract

Size effect of carboxymethyl chitin nanocrystals on foam and emulsion in aqueous surfactant solutions was investigated. The chitin nanocrystals (CNC) were synthesized by 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) oxidation of α-chitin at pH 10∼11 with ultrasonic treatment. The sizes of chitin nanocrystal (CNC) were controlled by adding different amounts of NaClO during the TEMPO oxidation reaction. The zeta potential of chitin nanocrystal was negative charge, so we introduced the cationic cetyltrimethylammonium bromide (CTAB) surfactant to made aqueous foam. The CNC was also freeze-dried to confirm the effect of surface charge and hydrophobicity in foam. The aqueous foams were made by cationic cetyltrimethylammonium bromide (CTAB) surfactant and CNC. With the freeze-dried CNC, foamability was increased by lowering the size of CNC, but foam stability was decreased. On the other hand, with the non-freeze dried CNC, foam stability was increased but foaming ability was decreased by lowering the size. The Cryo-SEM images demonstrated that CNCs were well adsorbed at air/water interface in foam, and improved foam stability by reducing the pressure difference between bubbles. In this study, the emulsion stability as varying different size of CNCs was investigated. The size of 200 nm improved emulsion stability the most. Moreover, the pH variation of 3, 7, 9 was researched to discuss about the change of carboxymethyl functional group in different pH. Emulsion viscosity difference was observed by a rheometer as the ratio of water and emulsion. Confocal Laser Scanning Microscope and Optical Microscope was used to visualize the adsorption ability of carboxymethyl chitin in emulsion. In consequently, we studied a new material of carboxymethyl chitin nanocrystals synthesized by the TEMPO-oxidized reaction over aspect of aqueous foaming and emulsion. TEMPO oxidized-chitin nanocrystals will be applied to emulsion and foam to replace the synthesized polymers. These days, chitin nanocrystals are novel materials in the colloids and surfaces due to the use of environmental Pickering stabilizer agent. Pickering foam and emulsion will be applied in the industry of cosmetic, pharmaceutical and food environmentally