Self-assembled "Supra-molecular" Structures via Hydrogen Bonding and Aromatic/Aliphatic Microphase Separation on Different Length Scales in Symmetric-Tapered Bisamides

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• 作者：Chenchen Xue ; Shi Jin ; Xing Weng ; Jason J. Ge ; Zhihao Shen ; Hong Shen ; Matthew J. Graham ; Kwang-Un Jeong ; Huabing Huang ; Dong Zhang ; Mingming Guo ; Frank W. Harris ; Stephen Z. D. Cheng ; Christopher Y.
• 刊名：Chemistry of Materials
• 出版年：2004
• 出版时间：March 23, 2004
• 年：2004
• 卷：16
• 期：6
• 页码：1014 - 1025
• 全文大小：716K
• 年卷期：v.16,no.6(March 23, 2004)
• ISSN：1520-5002

文摘

Self-assembled "supra-molecular" liquid-crystalline phases were investigated in one of aseries of symmetrically tapered bisamides based on an amide core of 1,2-bis[3,4,5-tris(alkan-1-yloxy)benzamido]benzene and three alkyl tails on each side of the core. One of this seriesof bisamides having 14 carbon atoms in each tail (abbreviated as C₁₄PhBA) served as anexample in this study. Differential scanning calorimetry thermal diagrams showed two mainphase transition processes in C₁₄PhBA. Wide-angle X-ray diffraction results revealed thatthe high-temperature phase transition is between the isotropic melt (I) and a 2D low-orderedoblique columnar phase (I _OB). The low-temperature phase transition was attributed tothe transition between a highly ordered, oblique columnar (_OK) phase and the _OB phase.Supra-molecular columns were directly visualized using transmission electron microscopyand atomic force microscopy. The formation of these supra-molecular structures is criticallydependent upon the construction of building blocks ("columns") by C₁₄PhBA molecules. Thesebuilding blocks developed via rigid amide core/alkyl tail micro-phase separation and thehydrogen (H) bond formation between the N-H and carbonyl groups among the cores.Spectroscopic studies showed that the columns were stabilized by intercore H-bonds orientedalong the column long axis, and the alkyl tails in the _OK phase were packed into an orderedmesophase having about 64% of the methylene carbon atoms in long trans segments at roomtemperature. In the _OB phase, the alkyl tails adopt liquidlike disordered conformations.The high- and low-temperature phase transitions were thus mainly attributed to the suddenchanges in H-bonding and alkyl tail conformation, respectively. A detailed packing model ofthe _OK phase was proposed and qualitatively proven using a simulated structural diffraction.