可加工的液晶态纳米纤维素流体材料：制备、性能及防伪应用

Owing to fake products seriously threaten economic development, human health, and national security, it is of great academic and application value to develop novel anti-counterfeit materials. Cellulose nanocrystal suspension that reach critical concentration could form cholesteric liquid crystals and obtain iridescent film after drying. However, strong hydrogen bond interactions among the hydroxyl groups of cellulose nanocrystals seriously restrict their anti-counterfeiting application. In this work, we attempt to chemically modify cellulose nanocrystals for construction of flexible ligands through electrostatic, host guest and hydrogen bonding interactions, resulting in surface functionalization of cellulose nanocrystals and preparation of solvent free nanocellulose fluid materials. The melting point, rheological property, and liquid crystal behavior of nanocellulose fluid materials were controlled by varying the aspect ratio of cellulose nanocrystals, as well as the chemical structure, molecular weight and interactions of ligands. The relationship between the structure and properties of nanocellulose fluid materials are investigated, and the mechanism of their formation, flow and cure are clarified. These novel nanomaterials not only well retain the cholesteric liquid crystal structure of cellulose nanocrystals, but also have processability. Special patterns are fabricated by printing and curing of nanocellulose fluid materials and their properties are investigated for the development of novel anti-counterfeiting labels. This project suggests a new direction for the high value utilization of renewable resources, and provides new ideas for the development of high-end anti-counterfeiting materials.

假冒伪劣产品严重威胁经济发展、人类健康和国家安全，开发新型防伪材料具有重要学术和应用价值。纤维素纳米晶体悬浮液达到一定浓度可形成胆甾型液晶，干燥后形成彩虹色薄膜，但其表面羟基间的强氢键作用严重限制材料的防伪应用。本项目拟对纤维素纳米晶体进行化学修饰，构建基于静电、主客体和氢键相互作用的长柔顺链配体，实现其表面功能化，制备无溶剂纳米纤维素流体材料。通过改变纤维素纳米晶体长径比、配体的化学结构、分子量和相互作用方式，控制纳米纤维素流体材料的熔点、流变性和液晶行为。研究纳米纤维素流体材料的结构和性能之间的关系，弄清其形成、流动以及固化机理。这类新型纳米材料既完整保留纤维素纳米晶体的胆甾型液晶结构又具有可加工性。将纳米纤维素流体材料打印、固化制成特定图案，研究材料的光学性能，开发新型防伪标识。本项目为可再生资源的高值化利用提供新方向，同时为高端防伪材料的开发提供新思路。

将天然纤维素纳米晶体转化为新型防伪材料具有重要学术意义和应用价值，而关键难点在于两方面：材料加工方面，由于纤维素纳米晶体间强氢键作用，需要先分散在溶剂中形成悬浮液，不能直接加工成防伪材料；材料性能方面，纤维素纳米晶体薄膜具有虹彩色，存在颜色不可控、力学性能较差的问题。本项目通过对纤维纳米晶体表面修饰，利用静电相互作用引入长柔顺链配体，成功获得无溶剂纳米纤维素流体。控制配体种类、摩尔取代度，实现了纳米纤维素流体剪切流动，静置固化。建立了纤维素纳米流体打印参数与防伪图案结构色之间的关系，并应用于纸币的防伪。另一方面，我们开发了一类纳米纤维素墨水，通过3D打印制备了具有单畴结构色的防伪图案。建立了打印层数和打印方向与纳米纤维素的排列方向和图案厚度间的关系，分别实现了基于亮度和色差的防伪图案的开发，包括高分辨的QR码，太极图和色卡。上述防伪材料在可见光下无色透明，在偏振光下显现预设的各种干涉色图案，在防伪和信息隐藏领域具有应用前景。这些工作总结在标注了本基金项目号的23篇论文中，其中影响因子大于10的论文15篇，5至10之间论文8篇，3篇被选为封面论文，授权国家发明专利1项。在此项目运行期间，共毕业硕士生4名，受邀在各种学术会议上做报告5次。