Surface charge regulated self-assembly and interfacial adhesion mechanisms of cellulose and chitin nanofibers

This study investigates how charged-group polarity, nanofiber morphology, substrate surface chemistry, and evaporation-assisted assembly jointly regulate the interfacial adhesion of cellulose and chitin nanofibers. Four nanofibers with amino or carboxyl groups were prepared, with charged-group densities of 0.50-1.46 mmol/g. Contact angle and XPS analyses revealed hydroxylated siloxane/silanol-rich glass and native oxide/hydroxide-covered copper surfaces. Statistical lap-shear tests showed substrate-dependent adhesion: DEChN reached 2.57 ± 0.05 MPa and 0.10 ± 0.02 MJ/m³ on glass, whereas TOCN reached 2.13 ± 0.01 MPa and 0.075 ± 0.004 MJ/m³ on copper. Nanofiber concentration, acid/base vapor atmosphere, and drying temperature further regulated strength, toughness, and strain at break by modulating interfacial packing and network cohesion. These results establish a surface-chemistry-guided assembly framework for sustainable water-borne nanofiber adhesives.