Compression-Induced Quasi-2D Assembly of Hydrophobized Cellulose Nanofibers at the Air-Water Interface

The interfacial assembly and rearrangement of nanomaterials are critical for stabilizing air-water/oil-water interfaces. Cellulose nanofibers (CNFs) are promising renewable bio-based solid surfactants that form stable interfacial layers separating the fluid interface. However, the correlations between microstructural features (e.g., defects, orientation, buckling) and physicochemical properties of the interfacial layer remain unclear. This study attempted to understand the interfacial behaviors of CNFs with different hydrophobicity through a common mechanism. First, nanofiber monolayers were fabricated on the water surface of a Langmuir trough. Three different regions corresponding to gaseous, liquid expanded, and liquid condensed films were determined from the characteristic points of surface pressure isotherms. The film structures and their surface dilatational storage/loss moduli exhibited significant changes across these three regions. Overall, we propose that the interfacial behaviors of nanofiber monolayers can be organized by macroscopic wettability of nanofibers which is readily measurable. These results provide insights into the interfacial stabilization mechanism of fibrous nanomaterials and pave the way for applications in functional Pickering emulsions/foams.