Functionalization of cellulose nanocrystal films using Non-Thermal atmospheric-Pressure plasmas

Dielectric barrier discharge plasma was used to functionalize cellulose nanocrystal (CNC) films. The plasma was induced in different gas mixtures: argon/methane (Ar/CH4), argon/ammonia (Ar/NH3) and argon/silane (Ar/SiH4). The functionalized samples were characterized by X-ray diffraction (XRD), water contact angle (WCA) measurements, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The wettability of the cellulose nanocrystals depends on the gas mixture while XRD demonstrate that plasma exposure does not affect the quality of the CNC films in terms of crystallinity. The WCA measurements indicate the presence of a hydrophobic surface after Ar/CH4 plasma exposure. XPS reveals that this hydrophobic behavior is related to an increase of the C-C/C-H bond concentration. In contrast, Ar/NH3 plasma exposure of the CNC films increases their hydrophilicity, which is due both to the formation of polar groups such as O-C=O/N-C-O and to an increase of the film surface roughness. Finally, exposing the CNC films to an Ar/SiH4 plasma yields a superhydrophobic coating due to the formation of SiO2 bonds on the film surface. These results demonstrate that plasmas with the appropriate chemistry can modify the degree of hydrophobicity and hydrophilicity of CNC films.