Molecular Origins of Emulsification by Polysaccharide Nanofibers: Effects of Crystal Surfaces and Chemical Structure

Abstract Cellulose nanofibers (CNFs) and chitin nanofibers (ChNFs) are biocompatible and biodegradable Pickering emulsifiers with excellent emulsifying capacity. However, the molecular origins of their emulsifying capacity remain unclear. Here, we combined emulsification experiments with molecular dynamics (MD) simulations to elucidate how the surface chemical structure governs the emulsifying capacity. Emulsification experiments showed that ChNFs consistently outperform CNFs across all oils tested. MD simulations revealed that partial conversion of hydroxymethyl groups to carboxylate groups through the TEMPO-oxidation significantly increased the hydrophilicity of the cellulose surfaces and decreased the three-phase contact angle formed among the water, oil, and cellulose surface, reducing the emulsifying capacity. In contrast, the conversion of acetamide groups to protonated amino groups through deacetylation of chitin increased hydrophilicity without causing complete wetting, maintaining the three-phase contact angle and emulsifying capacity. These results guide the rational design of polysaccharide-stabilized Pickering emulsions and deepen the fundamental understanding of cellulose and chitin surfaces.