兼具可控结构色和发光性能柔性纳米纤维素膜的构建与性能调控机理研究

Coloration in nature acts important roles in signaling, mimicry and mate choice. Compared with pigment coloration, the charming colors on some surfaces of animals and plants are observed only arising from the interaction between light and their hierarchical structures. This is known as structural coloration, and generally iridescence is found associated with this phenomenon. Very recently, fabrication of nanostructures to mimic the nature has made a great progress for application in fields of display technologies, printing, painting, cosmetics and textiles.. Cellulose nanocrystal (CNC) obtained from the sulfuric acid-catalyzed hydrolysis of bulk cellulose can form chiral nematic phases in water. Once dried to a solid state, CNC can retain a layered structure where aligned orientation exists within each layer. The corresponding films are iridescent upon reflection of left-handed circularly polarized light if their pitch length is on the order of the wavelengths of visible light. Thereafter, exploring effective methods to modulate the coloration of iridescent films has attracted much attention in the past decades. The reflected color can be tuned across the visible region by adding sugar (red shift in color) or monovalent salts (blue shift), sonication before solvent-evaporation (red shift), and changing drying temperature (blue shift in the case of a high temperature). However, over-sonication or the addition of an excess of salt/sugar may block the self-assembly of CNC irreversibly, resulting in the loss of iridescence. In fact, there is strict restriction for the gelation of CNC if iridescent films are to be obtained. Gelation must occur at the concentration above the initial critical concentration of the chiral nematic phase separation, or only transparent isotropic nonbirefringent films are prepared. When gelation occurs at pitch values outside the visible light region, no iridescent color is to be obtained, too. To interpret the color changes of solid CNC films, almost the all reports just focus on the effect of modifications on the pitch of CNC rather than its gelation behaviors. Therefore, according to current theories, it is difficult to predict the effect of additives on pitch length at equilibrium state. In addition, the iridescent films have serious brittleness, which is another obstacle against applications. Although some works have overcome this drawback, the iridescence is lost and the biodegradability is impaired because of introducing non-degradable polymers. .Recently, incorporation of functional dopants into photonic crystals has been proved to fabricate waveguide-based devices successfully. Thanks to the broad absorption spectra, narrow emissions, high quantum yield, and long fluorescence lifetime, carbon quantum dot (CQD) is an ideal light emitter with tunable emissions. On the other hand, flexible films with multi-layered structures can be prepared from brittle materials via layer-by-layer technology, in which cellulose nanofiber (CNF) were employed as the supporting layers. . In this project, therefore, we propose to synthesize a series of CNC, CNF, and CQD with different morphologies, and prepare bi-/multi-layered flexible cellulose films with optical functions by selecting flexible CNF film and light-emitting CNC/CQD iridescent film as the supporting and functional layers, respectively. The effects of the size and amount of CQD on the gelation behavior, fractal structure and liquid-crystalline texture of CNC will be investigated, and the relationship among the layered structure, mechanical property, stability, and biodegradability of resultant films will be established. Based on the above researches, we can obtain novel flexible all-cellulose films with both physically structural color and chemically light-emitting property, which can expand the application of cellulose towards the field of flexible optical devices, suggesting that the project is of great significance and has important scientific value.

利用纤维素纳米晶须（CNC）自组装形成手性向列型液晶结构生色的性质构建彩色薄膜，近年来成为生物基高分子材料领域的研究热点，但如何在保持结构色可控的前提下，提高材料的韧性并丰富其功能仍是有待解决的科学问题。本项目拟采用水分散性碳量子点和纤维素纳米纤维（CNF）对CNC进行改性，通过层层复合构筑以CNC/碳量子点复合膜为光学功能层、CNF膜为支撑层的双/多层膜。研究量子点尺寸与添加量对CNC的凝胶化转变、分形结构、液晶织构等的影响，以及CNF的形貌和复合膜层结构对力学性能、光学性能、降解性能等的影响，阐明量子点和CNF的引入与材料结构色、光致发光性能、力学性能之间的内在联系，提出光学和力学性能调控的关键机理。通过上述研究有望获得兼具可控物理结构色和化学发光性能的柔性纳米纤维素膜，为拓展纤维素这一传统材料在光学安全加密及环境信号传感方面的应用提供崭新的研究思路，具有显著的研究意义和科学价值。

利用纤维素纳米晶（CNC）自组装形成手性向列型液晶结构制备具有结构色的功能材料近年来受到了广泛关注，但如何在保持结构色可控的前提下，提高材料的柔韧性并拓展其功能是该领域有待解决的关键问题。为此，本项目分别将乙醇胺、甘油、柠檬酸、聚乙二醇交联网络和聚二甲基二烯丙基氯化铵等与CNC复合，构建了一系列具有柔性结构色膜材料。具体包括：将带不同电荷的小分子增塑剂与CNC共混，以改善其力学性能，并研究了共混膜对多种环境信号的传感性能；在此基础上，在CNC基体中构建聚合物交联网络，以实现CNC膜的高韧性和拉伸变色功能；为了进一步解决CNC膜普遍存在明显虹彩效应的局限性，利用溶液共混法将带相反电荷的聚电解质与CNC复合，以调控自组装结构的长程/短程有序性，制备非虹彩结构色CNC膜。系统研究了不同组分引入对CNC自组装及液晶行为、微观形貌、表观颜色、力学性能、环境信号传感性能等影响，阐明了CNC基多相体系共组装行为的调控机制，制备了系列具有化学和机械响应变色功能的CNC材料。项目研究结果为构建柔性结构色纤维素膜的研究提供了新思路，为拓展纤维素材料在光学安全加密、环境信号传感等方面的应用提供了科学依据。. 相关研究结果在Advanced Functional Materials、Chemical Engineering Journal、ACS Applied Materials & Interfaces、ACS Sustainable Chemistry & Engineering等期刊上发表论文16篇，其中第一标注13篇，第二标注3篇；授权中国发明专利2项。