Visualizing Dynamic Interfacial Assembly in Pickering Emulsions with Fluorescent Cellulose Nanofibers.

The dynamic interfacial adsorption behavior of cellulose nanofibers (CNF) in Pickering emulsions (PE) remains poorly understood at the molecular scale. Here, we present a fluorescence-grafted CNF strategy to directly visualize and analyze these processes. Oil-in-water PE are prepared using acridon-2-yl-alanine-grafted TEMPO-oxidized CNF (Acd-CNF) and Nile Red-stained dodecane as the oil phase. This system retains aqueous dispersibility and enables the detection of molecular proximity between the two fluorophores as an interfacial fluorescence response. Time-lapse confocal laser scanning microscopy reveals that the slowly introduced Acd-CNF dispersions spontaneously adsorb onto preformed TEMPO-oxidized, CNF-stabilized PE, leading to the formation of heterogeneous and multilayered interfacial architectures rather than a uniform monolayer. These findings indicate that CNF adsorption at oil-water interfaces proceeds through dynamic and hierarchical processes, challenging simplified static models of PE stabilization. Extension of this approach provides a new experimental framework for the rational design of PE and interface-engineered soft materials.