Optimization of Cellulose Nanocrystal Stabilized Emulsions through Surface Modification and Oil Phase Interactions

Abstract

Cellulose nanocrystals (CNCs) have emerged as promising bio-based Pickering emulsion stabilizers owing to their renewability, high aspect ratio, and excellent colloidal stability. This thesis explores strategies in optimizing CNC-stabilized emulsions through surface modification of CNCs and elucidating their interactions with oil-phase amphiphilic molecules. Pristine anionic CNCs were modified by grafting quaternary ammonium groups and quaternary ammonium surfactants to produce cationic CNC (P-CNC) and surfactant CNC (S-CNC), respectively. These materials were evaluated as stabilizers for hexane-in-water emulsions in combination with dodecylamine (DDA) and lauric acid (LA). Pristine CNCs exhibited strong synergistic interactions with DDA, producing highly stable emulsions with decreasing droplet size and enhanced viscoelasticity with increasing CNC concentration. In contrast, pristine CNC–LA emulsions displayed antagonistic interactions, where increasing CNC concentration produced larger emulsion droplets with better resistance to creaming and enhanced viscoelasticity. Surface modification to produce P-CNC reversed these trends, demonstrating that particle surface charge governs interactions with oil-phase amphiphiles through electrostatic interactions. S-CNC possessed substantially higher interfacial activity than pristine or cationic CNCs. It yielded stable emulsions with the smallest droplets. However, these emulsions possessed comparatively weak rheological properties despite their small droplet size. Overall, these findings demonstrate that modifying CNC surface chemistry provides a versatile strategy for tailoring emulsion droplet size, rheology, and stability. This work also reveals previously unexplored interactions between aqueous-phase cellulose nanoparticles and oil-phase amphiphilic molecules, providing new insights into the rational design of sustainable emulsions with tunable interfacial and bulk properties for diverse applications.