CO2 gas-triggered wettability control of silylation-modified CNC films by manipulating the surface structure and introducing tertiary amino groups

Here, cellulose nanocrystal (CNC) films were chemically modified in a two-stage process to realize surface wettability control through the introduction of CO2 gas. In addition to controlling the surface structure of the silylation-modified CNC film, functional groups derived from silane compounds were installed, and the corresponding effects on the resulting chemical modification were investigated. In the first stage, methyltriethoxysilane (MTES) and hexyltriethoxysilane (HTES) combined with tetraethoxysilane (TEOS) were subjected to condensation under alkaline conditions. In the second stage, (3-(N,N-dimethylamino)propyl)trimethoxysilane (DMAPS) generated an amino group to control the surface wettability by adsorption CO2 gas. Then, the silylation-modified CNC film was fabricated on a glass substrate by spin coating. Fourier transform infrared (FT-IR), nuclear magnetic resonance (29Si-NMR), and X-ray photoelectron spectroscopy (XPS) inspection indicated that the silane compounds were bonded to the CNC film surface and that tertiary amino groups were successfully introduced. The surface structure of the silylation-modified CNC film was analyzed by atomic force microscopy (AFM), and the surface roughness calculating indicated a root-mean-square roughness (RMS) of 4.2 nm. The water contact angles before and after the CO2 gas treatment were evaluated as 73o and 22o, respectively. The modification of cellulose nanocrystal film using alkyl silane and silane containing tertiary amino groups was performed in a suspension state. Control of the surface structure and functionalization by silane compounds was conducted in the two-stage process. Wettability change property of the silylation-modified CNC triggered by CO2 was demonstrated.