甲壳素纳米晶体向列型液晶薄膜的组装及其光学性能研究

Assembly and Optical Properties of Nematic Liquid Crystal Films from Chitin Nanocrystals

针对甲壳素光子晶体材料无法呈现可视化颜色的问题,设计构筑了一种具有向列型结构的甲壳素液晶薄膜材料.该液晶薄膜材料由羧基化甲壳素纳米晶体(T-ChNC)通过羧基基团间的静电排斥作用和空间位阻作用在水相中自组装形成的向列型液晶干燥而成.在自然光下,液晶薄膜表现高透明度,而由于高度取向排列的结构对光具有干涉作用,正交偏光镜下的薄膜呈现鲜亮的蓝色.T-ChNC表面羧基基团的密度显著影响T-ChNC在水相中的静电作用范围,进而影响薄膜中T-ChNC的取向度,当羧基含量高于0.6 mmol/g且T-ChNC分散液的浓度高于5%时,干燥的T-ChNC液晶薄膜可表现均匀的颜色.实验表明,强亲水性的T-ChNC薄膜对湿度和溶剂具有敏感的响应性,在高湿度环境中发生润胀并转变颜色,在不同浓度乙醇溶液中表现不同的颜色变化.与传统的甲壳素手性光子晶体材料相比,向列型T-ChNC液晶薄膜具有肉眼可见的颜色且色彩可设计调控,在生物光学防伪和加密材料方面具有广阔的应用前景.

To solve the problem that chitin photonic crystals material cannot exhibit visual color,a chitin liquid crystal film material with nematic structure is designed and constructed.The liquid crystal film material is dried from nematic liquid crystal formed by self-assembly of carboxylated chitin nanocrystals(T-ChNC)in the aqueous phase through electrostatic repulsion and steric hindrance between carboxyl groups.The liquid crystal film exhibits high transparency under natural light,and due to the light interference effect of the highly aligned structure,the film exhibits a bright blue color under the crossed polarizer.The density of carboxyl group on the surface of T-ChNC has significant effects on the range of electrostatic repulsion force of T-ChNC in water,which in turn affects the orientation degree of T-ChNC in the film.When the carboxyl content is higher than 0.6 mmol/g and the concentration of T-ChNC dispersion is higher than 5%,the dried T-ChNC films have uniform color.It is shown that T-ChNC films with strong hydrophilicity have sensitive responsiveness on ambient humidity and solvent,swelling and changing color in high humidity atmosphere,and showing various colors in ethanol solutions with different concentrations.Compared with the traditional chitin chiral photonic crystal material,the color of the nematic T-ChNC liquid crystal film is visible and can be controlled by design,which has broad application potential in bio-optical anti-counterfeiting and encryption materials.