Effect of carboxyl on wettability and anti-fingerprint capacity of transparent chitin nanofiber coatings modified using fluorosilane

Chitin nanofibers (ChNFs) with different numbers of carboxyls (i.e., with different degree of substitute, DS) were prepared by adjusting the amount of maleic anhydride used in the acylation treatment prior to mechanical nanofibrillation with ultrasound. Transparent coatings were fabricated by using the obtained ChNFs through casting method and modified via vapor deposition by using 1H, 1H, 2H, 2H-perfluorodecyltrichlorosilane (PFDTS). Hydro-oleophobicity and anti-fingerprint capacity of the ChNF coatings were studied. It was found that the ChNF coatings with more carboxyls possessed stronger hydro-oleophobicity as well as anti-fingerprint capacity after the modification of PFDTS deposition. Analysis of X-ray photoelectron spectroscopy suggested that more PFDTS molecules were grafted onto the ChNF coating surface when the ChNFs had more carboxyls (with higher DS). It is the number of carboxyls rather than hydroxyls on ChNF coating surface that determines hydro-oleophobicity and anti-fingerprint capacity of the ChNF coating surface after the modification of the PFDTS deposition.