Decoupling interfacial and bulk stabilization in beeswax-in-water Pickering emulgels using carboxylated cellulose nanofibers

This work reports the formation of beeswax-in-water Pickering emulgel architectures stabilized solely by TEMPO-oxidized cellulose nanofibers (TOCNFs). Stable emulgels were obtained at a low critical stabilization concentration of 0.2 wt% TOCNF, irrespective of the nanofiber degree of carboxylation (DC). The dominant stabilizing mechanisms involve the irreversible interfacial adsorption and assembly of TOCNFs, providing surface coverage, combined with the formation of a hierarchical entangled fibrillar network in the continuous phase. The carboxylate groups at the surface of TOCNFs impart electrostatic repulsion, leading to a gel-like rheology that arrests the Brownian motion of the wax particles. This network effectively acts as a supramolecular cage trapping the dispersed wax particles and providing a macroscopic yield stress to the system. Rheological analysis revealed that the yield stress is governed primarily by TOCNF concentration and network architecture, with DC exerting a secondary but measurable effect via the degree of fibrillation and the resulting aspect ratio which dictates the extent of physical entanglement. The frequency dependence of the storage and loss moduli indicates that the TOCNF-stabilized beeswax emulgels behave as a structurally arrested soft-glassy system, suggesting that macroscopic elasticity is dominated by the jamming of TOCNF-coated wax particles and by the topology of the physical entanglement. TOCNF shells preserved 85% of bulk beeswax latent heat, while inducing a 7 °C crystallization depression attributed to confinement and fractionated nucleation. These findings quantify the dual effect of interfacial and bulk assembly in semi-flexible fibril systems and demonstrate routes to design fully bio-based coatings, phase-change materials and encapsulation formulations with tunable rheological and thermal properties.