Understanding of Molecular Packing in Thermotropic Cubic Phase and Control of the Formation

本研究项目的目的是，第一，了解在热致立方（立方）中间相的分子堆积结构，第二，阐明从层状近晶C（SmC）立方相的相变机制，第三，控制立方相的形成。我们重点关注两个同系物，4 '-n-烷氧基-3'-硝基联苯-4-羧酸（ANBC）和1，2-双（4 '-n-烷氧基苯甲酰基）肼（BASH）。在两个同源系列中，构成SmC和Cub相的基本单元具有共同的结构，由在中心具有氢键部分的芳香族核心部分和在每个末端的烷基尾组成。获得了以下见解：对于两个同系，相图作为温度，压力和烷基链长度的函数已经建立。ANBC系列显示两种类型的Cub相，Ia 3d型和Im 3 m型，高于SmC相的温度区域。提出了两种立方相的分子堆积模型。BASH系列也显示SmC相和Cub相，但SmC相仅在烷氧基链中的碳原子数（n）为8、9或10时形成。当n=7-12时，Cub相的相类型属于Ia 3d。通过比较两个系列的相行为，揭示了烷基尾和中心氢键部分在Cub相形成中的作用。也就是说，Cub相形成的一个关键起源是SmC层内温度引起的堆积挫折，这是由于烷基尾部与芳族核心部分之间的界面处的不对称形状，就像溶致体系中的非极性与极性竞争一样，因此，准二元图像对于理解整个行为是非常有效的。然而，在热致体系中，分子间相互作用的其他贡献，如氢键，偶极-偶极相互作用等的存在也是重要的，并改变相的形成。

The aim of this research project is, first, to understand the molecular packing structure in the thermotropic cubic (Cub) mesophase and, second, to elucidate the phase transition mechanism from a lamellar smectic C (SmC) to Cub phase, and, third, to control the formation of the Cub phase. We focused attention to two homologues, 4'-n-alkoxy-3'-nitrobiphenyl-4-carboxylic acids (ANBC) and 1,2-bis(4'-n-alkoxybenzoyl)hydrazines (BASH). In the two homologous series, the basic units constructing the SmC and Cub phases have a common structure, consisting of an aromatic core moiety with a hydrogen-bonding part at the center and an alkyl tail at each end. The following insights were obtained :For the two homologous series, the phase diagrams as functions of temperature, pressure, and alkyl chain length have been established. The ANBC series shows two types of Cub phases, Ia3d-type and Im3m-type, above the temperature region of the SmC phase. The molecular packing models of both Cub phases were proposed. The BASH series shows also SmC and Cub phases, but the SmC phase are formed only when the number of carbon atoms in the alkoxy chain (n) is 8, 9, or 10. The phase type of the Cub phase belongs to Ia3d for n=7-12. Comparing between the phase behaviors of the two series, the roles of the alkyl tail and central hydrogen-bonding part for the Cub phase formation have been revealed. That is, a key origin for the Cub phase formation is temperature-induced packing frustration within SmC layers due to unsymmetrical shape at the interface between the alkyl tail vs aromatic core parts, just like apolar vs. polar competition in lyotropic systems, and therefore, the quasi-binary picture is quite effective for understanding the whole behaviors. In the thermotropic systems, however, the presence of other contributions of intermolecular interactions such as hydrogen-bonding, dipole-dipole interactions etc. is also important and modifies the phase formation.