树枝状分子中具有准周期性有序及其相关液晶结构及自组装机理研究

Quasicrystal is a quasiperiodic ordered structure with extraordinary symmetry, such as five- and ten-fold symmetry. Recently a liquid quasicrystalline structure with twelve-fold symmetry was observed in dendrimers and this is the first report to find quasicrytalline structure in organic materials. This experimental finding might provide a new proposal for the solution of Kelvin Problem, which is the structure with minimum surface area to fill the whole space. This research proposal would study more deep and widely in this research topic. Taking the advantage of features of soft matter, such as flexibility and enviromental- sensitivity, a series of dendrimers focusing on alkali metal salts with various funtional groups would be studied, to regulate the self-assembly behavior of supramolecules through the molecular design of topologic structures, the various thermodynamic parameters including counterion, temperature. Utilizing of the technologies of synchrotron radiation and small-angle X-ray scattering (SAXS), the relationship between molecular or thermodynamic parameters and the phase behaviors of condensed matter will be discussed. The reconstruction of electron density map would be done to build the parameter space with liquid quasicrystalline order. Furthermore, the methods of glazing incident small-angle X-ray scattering (GISAXS) and high-resolution microscopy would be tried, to give assistance in solving the unknown liquid crystalline structres and looking for novel liquid quasicrystals. This proposal would be expected to accumulate the experimental data for finding mechanism of soft quasicrystalline order, and the self-assembly models would be proposed for better understanding of the self-assembly behaviors. Meanwhile, more efficient and direct experimental evidences for better solution of Kelvin Problem would be achived.

准晶是具有五次、十次旋转等特殊对称性的准周期性有序结构。近年在树枝状分子中观测到具有十二次旋转对称的液态准晶结构，是首次在有机分子体系中发现准晶结构。同时为开尔文问题（三维空间堆砌所需要的具有最小表面能的结构）最佳解提供了新的可能。本项目将拓展和深入这一研究，利用软物质的柔性和环境敏感特点，以具有不同官能团的碱金属盐等树枝状分子作为研究对象，从分子的拓扑结构设计、反离子、温度等热力学参数出发调控超分子自组装行为。利用同步辐射X射线小角散射技术，并借助电子密度重构结构解析方法，研究分子参数-热力学参数与凝聚态相行为的关系，构建液态准晶有序的参数空间。同时还将尝试采用掠入射小角散射方法及高分辨电镜作为液晶相结构研究的辅助手段，解析未知的液晶相结构，寻找不同类型的液态准晶。既为有机准晶有序机理的构建积累实验数据，提出自组装模型理解自组装过程，也为"开尔文问题"最佳解提供更加高效和直观的实验证据。

液晶是一种介于晶体和液体之间的具有独特周期性有序的物质形态，它具有良好的自组装行为能力。本研究设计合成一系列新型液晶化合物，利用同步辐射小角X射线散射技术手段，并借助电子密度重构结构解析方法，理解液晶相转变过程及自组装行为。在选取的最佳类型液晶自组装体系的树枝状分子体系中，设计并合成得到了具有不同长度烷基链和不同位置上的链取代的 AB5 型锥形树枝状分子，其液晶相行为与我们之前提出的关于楔形分子的形状与介晶相态之间关系的dv⁄dr径向分布曲线很好吻合。在带有3，4，5位含氧烷基链的树枝基元体和烷烃复合体系中观察到了一种柱状超晶格结构。在含有三种不同亚甲基MBPE-X、FBPE-X和ClBPE-X的不同个数（5，7，9）柔性间隔的液晶高分子中观察到新型向列相-向列相转变。本研究对于液晶自组装行为提供了更为丰富的理解和模型。