| Cellulose nanocrystals(CNC), prepared by the acid hydrolysis of wood, cotton or other cellulose-rich raw materials, have been known for more than 50 years since it was first produced. Their fascinating properties such as high specific strength and modulus, high specific surface area, and unique optical properties have attracted significant interest. However, until rencently, their ability in templating was discovered by utilizing their self-assembly behavior in water with suitable precursors, in order to develop new functional materials with chiral nematic order and distinct optical properties. In this paper, on one hand, chiral nematic mesoporous silica films was frabicated by mixing CNC suspension with silica precursor and removing the templates next. On the other hand, stimuli responsive CNC/WPU composite films with chiral nematic order was prepared by blending CNC suspension with waterborne polyurethane (WPU) latex. The main contents are as follows:1、CNC was prepared by sulphuric acid hydrolysis of microcrystalline cellulose(MCC). TEM and AFM observation confirmed that CNC were 100-300nm in length and ca.10 nm in width. XRD analysis showed that the crystallinity of CNC was increased to 89% after acid hydrolysis. The fingerprint texture representative of the chiral nematic phase was observed by polarizing optical microscopy.2、Chiral nematic mesoporous silica films was prepared by first mixing CNC suspension with tetramethyloxysilane(TMOS),allowing the mixture to dry under ambient conditions, and then removing the CNC by calcination or acid hydrolysis. The color of the film could be tuned by changing the proportion of silica precursor relative to CNC. SEM and TEM observation confirmed the replication of chiral nematic organization in mesoporous silica films. Nitrogen absorption-desorption studies showed the mesoporous silica film had a BET surface area about 259 m2/g and BJH peak pore diameter of ca.9.6nm. Mesoporous films show strong birefringence under POM.3、CNC/WPU composite films with chiral nematic order was prepared by mixing CNC suspension with WPU latex under nearly neutral pH conditions, then allowing it to dry under ambient conditions. The color of the films could be tuned by changing the content of WPU in the composites. SEM observation confirmed that the helical pitch of the composites increased with the increasing content of WPU. The tensile strength of the composite films increased at first and then decreased as the WPU content increased, while the elongation at break kept increasing. In addition, both the composite films and composite coating on glass substrate could change color in response to the differences in solvent polarity, water and humidity, which have potential applications in sensor and smart coating materials. |
