Responsive and patterned cellulose nanocrystal films modified by N-methylmorpholine-N-oxide

A type of cellulose solvent, i.e., aqueous N-methylmorpholine- N-O xide (NMMO) solutions, was used to modify cellulose nanocrystal (CNC) photonic films. CNC films can be swollen by NMMO, resulting in red-shifted reflected colors. The swelling effect is supposed to come from NMMO permeation into the crystalline regions of individual CNCs and intercalating in between CNC particles. When NMMO was removed, the reflected colors of CNC films blue shifted because of the reduced helical pitches. NMMO-treated CNC films display reversible responsive colors to humidity changes in several minutes. Increasing NMMO content allows CNC films to enlarge the responsive color range. Aqueous NMMO can be used as an ink to depict responsive photonic patterns on CNC films. This post-treatment approach to producing responsive colors and photonic patterns in CNC films may be applied to the areas of sensor, anti-counterfeiting, and decoration.