Polar Switching in Trialkylbenzene-1,3,5-tricarboxamides
Polar Switching in Trialkylbenzene-1,3,5-tricarboxamides
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DOI：
10.1021/jp300008f
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发表时间：
2012-04-05
影响因子：
3.3
通讯作者：
Sijbesma, Rint P.
中科院分区：
文献类型：
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作者：
Fitie, Carel F. C.;Roelofs, W. S. Christian;Sijbesma, Rint P.
由苯-1,3,5-三羧基酰胺（BTA）衍生物形成的氢键六方柱状LC （Col(hd)）相在电场作用下可以均匀排列，并显示出高残余极化的开关行为。通过电光开关实验、介电弛豫光谱（DRS）和固态核磁共振（NMR）研究了3种长度在6到18个碳原子之间的烷基链（C6、C10和C18）对称取代bta的极性开关。目的是表征基于bta的柱状LCs的铁电性质，其表现出由于氢键酰胺首尾堆叠而产生的宏观轴向偶极矩。C10和C18的残余极化和矫顽力场分别为1-2 μ C/cm(2)和20-30 V/ μ m，表现出外在极性开关特性。在没有外场的情况下，极化在1-1000秒内损失，这取决于器件的细节和温度。DRS揭示了LC相低温区域的柱状玻璃化转变，这与在41-54℃以下冻结的氢键柱的集体振动有关。在较高温度下，由于酰胺基团沿着柱轴的集体重定向（大偶极子反转），出现了弛豫过程。匹配的活化能表明极性转换和r过程的分子机制是相同的。这些结果表明，基于bta的LC相提供了在单个纳米结构材料中集成极化与其他功能的独特可能性。
The hydrogen-bonded hexagonal columnar LC (Col(hd)) phases formed by benzene-1,3,5-tricarboxamide (BTA) derivatives can be aligned uniformly by an electric field and display switching behavior with a high remnant polarization. The polar switching in three symmetrically substituted BTAs with alkyl chains varying in length between 6 and 18 carbon atoms (C6, C10, and C18) was investigated by electro-optical switching experiments, dielectric relaxation spectroscopy (DRS), and solid-state NMR The goal was to characterize ferroelectric properties of BTA-based columnar LCs, which display a macroscopic axial dipole moment due to the head-to-tail stacking of hydrogen-bonded amides. The Col(hd) phase of all three BTAs can be aligned uniformly by a dc field similar to 30 V/mu m. Moreover, C10 and C18 display extrinsic polar switching characterized by a remnant polarization and coercive field of 1-2 mu C/cm(2) and 20-30 V/mu m, respectively. In the absence of an external field, the polarization is lost in 1-1000 s, depending on device details and temperature. DRS revealed a columnar glass transition in the low-temperature region of the LC phase related to collective vibrations in the hydrogen-bonded columns that freeze out below 41-54 degrees C. At higher temperatures, a relaxation process is present originating from the collective reorientation of amide groups along the column axis (inversion of the macrodipole). Matching activation energies suggest that the molecular mechanism underlying the polar switching and the R-processes is identical. These results illustrate that LC phases based on BTAs offer the unique possibility to integrate polarization with other functionalities in a single nanostructured material.