Effect of Counterion Choice on the Stability of Cellulose Nanocrystal Pickering Emulsions

Cellulose nanocrystals (CNCs) with three different counterions (H+, Na+, K+) were used to prepare oil-in-water Pickering emulsions with and without salt; their stability to coalescence and resistance to creaming were tested using two oil types (high-polarity corn oil and superlow polarity hexadecane). Without salt, only acid-form CNCs could stabilize corn oil emulsions, whereas the salt-form Na+-CNCs and K+-CNCs failed. None of the CNCs could stabilize hexadecane/water emulsions due to the lack of oil-CNC interactions and strong repulsion between CNCs. However, adding salt masked the differences between the CNC types, and all CNCs could stabilize both corn oil and hexadecane emulsions. Unfortunately, when salt was added, extensive creaming occurred owing to the water-phase density increase and droplet aggregation. The effect of salt concentration and neutralization of CNCs by different methods was also investigated. This work highlights the complex nature of CNC interactions with salts, oils, acids/bases, and other additives, which is relevant for envisioned formulated products for food, cosmetic, and pharmaceutical applications and reveals that the choice of CNC counterion does influence emulsion performance.