Ion-responsive liquid crystals of cellulose nanowhiskers grafted with acrylamide

In order to develop a novel application for cellulose nanowhiskers (CNW) produced from the sulfuric acid hydrolysis of cotton, acrylamide (AM) was grafted onto the CNW. The graft reaction of the acrylamide-grafted CNW (AM-g-CNW) was confirmed by Fourier transform infrared spectroscopy (FTIR) and UV-vis spectroscopy. The carbon and nitrogen contents of the AM-g-CNW were measured by elemental analysis and X-ray photoelectron spectroscopy (XPS). The grafting ratios and average degrees of β-1,4-linked anhydro-d-glucose unit substitution were measured. The thermochemical properties of the AM-g-CNW were characterized using thermogravimetric analysis (TG). The glass transition temperatures were determined by differential scanning calorimetry (DSC). The degrees of crystallinity were measured by X-ray diffraction (XRD). The liquid crystalline properties of AM-g-CNW were observed by polarizing optical microscopy (POM). AM-g-CNW had the best grafting ratio, 12.77%, when the AM/CNW molar ratio was 3, c(K2S2O8)/n(CNW) was 0.15, the reaction temperature was 70 °C, and the reaction time was 60 min. The birefringence of AM-g-CNW was responsive to hydroxide ions, which might be useful in applications that benefit from sensitivity towards different ionic species.