Interfacial jamming of surface-alkylated synthetic nanocelluloses for structuring liquids

Nanocelluloses derived from natural cellulose sources are promising sustainable nanomaterials. Previous studies have reported that nanocelluloses are strongly adsorbed onto liquid-liquid interfaces with the concurrent use of ligands and allow for the structuring of liquids, that is, the kinetic trapping of nonequilibrium shapes of liquids. However, the structuring of liquids using nanocelluloses alone has yet to be demonstrated, despite its great potential in the development of sustainable liquid-based materials that are biocompatible and environmentally friendly. Herein, we demonstrated the structuring of liquids using rectangular sheet-shaped synthetic nanocelluloses with surface alkyl groups. Synthetic nanocelluloses with ethyl, butyl, and hexyl groups on their surfaces were readily prepared following our previous reports via the self-assembly of enzymatically synthesized cello-oligosaccharides having the corresponding alkyl groups. Among the alkylated synthetic nanocelluloses, the hexylated nanocellulose was adsorbed and jammed at water-n-undecane interfaces to form interfacial assemblies, which acted substantially as an integrated film for structuring liquids. These phenomena were attributed to the unique structural characteristics of the surface-hexylated synthetic nanocelluloses; their sheet shape offered a large area for adsorption onto interfaces, and their controlled surface hydrophilicity/hydrophobicity enhanced the affinity for both liquid phases. Our findings promote the development of all-liquid devices using nanocelluloses.