Cellulose Nanocrystals Cholesteric Liquid Crystal Films Sensing On Acid Gas/Vapor

Cellulose nanocrystals have great potentials in gas monitoring due to their unique cholesteric liquid crystal property. Cellulose nanocrystals can be given more properties by chemical modification or incorporation of inorganic materials, thus leading to a broader range of potential applications.Cellulose nanocrystals suspension was prepared from microcrystalline cellulose by using sulfuric acid hydrolysis supported by ultrasonic. Then the as-prepared cellulose nanocrystals suspension was modified with ammonia solution, and then cast into films. The characterization results of atomic force microscopy (AFM) and Malvern particle size analysis showed that the as-prepared cellulose nanocrystal had uniform size and stable dispersion in water. The characterization results of optical fiber spectrometer and polarized optical microscopy showed that the color of films shift from yellow to blue, and the distance between the fingerprints of the films decreased from 1.076 to 0.698μm with the increased amount of ammonia solution,.Then the as-prepared cellulose nanocystals films were used for hydrochloric acid, acetic acid and CO2 sensing. The optical fiber spectrometer was employed to record the spectra of the films during the whole monitoring process. The results showed that the maximum reflection wavelength of the films presented a red shift during all the sensing process, and the time of reaching sensing equilibrium was HCl> HAc> CO2.To further investigate the influence of amino compound on the structure of cellulose nanocrystals. The ammonium sulfate and ferric sulfate/ferrous sulfate modified cellulose naocrystals films were prepared, respectively. The optical properties of the films were obtained from the optical fiber spectrometer and POM The results showed that the color of films changed due to the adding of amino compound. The maximum reflection wavelength of the ammonium sulfate films increased from 334.3 to 663.4 nm, and the distance of their fingerprints became broaden with the increased adding amount of ammonium sulfate. Meanwhile, the maximum reflection wavelength of ferric sulfate/ferrous sulfate modified cellulose naocrystals films decreased from 564.5 to 457.5 nm, and planar mesophases were not continuous with the increased adding amount of ammonium sulfate.