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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >~(129)Xe Nuclear Shielding and Diffusion in the A and C~* Phases of a Chiral Smectogen
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~(129)Xe Nuclear Shielding and Diffusion in the A and C~* Phases of a Chiral Smectogen

机译：〜（129）Xe在手性表面活性剂的A和C〜*阶段的核屏蔽和扩散

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摘要

The ~(129)Xe NMR shielding and diffusion of xenon dissolved in the chiral liquid-crystal 1-methylheptyl 4'-(4-n-decyloxybenzoyloxy)biphenyl-4-carboxylate (10B1M7) were studied over the temperature range covering the isotropic (I), smectic A (SmA), and ferroelectric, ferrielectric, and antiferroelectric smectic C~*(SmC~*) phases. The ~(129)Xe shielding reveals clearly the I-SmA and SmA-SmC~*(ferroelectric) phase transitions. The SmC~* sub-phase transitions can also be detected by smaller but distinguishable shifts of the shielding accompanied by line width changes. A theoretical model developed earlier is applied to the shielding data, confirming a negative anisotropic contribution to the shielding as the SmA phase forms and allowing the evaluation of the tilt angle in the SmC~*. Diffusion experiments were mostly performed in the direction parallel to the layer normal, i.e., along the external magnetic field, D_(||), in the smectic phases but a few experiments were carried out in the in-plane direction, i.e., perpendicular to the external magnetic field, D_⊥, as well. These experiments indicate large anisotropy, D_⊥/D_(||), of the ~(129)Xe diffusion tensor that increases as the temperature decreases. Application of the Arrhenius equation to the temperature-dependence of D_(||) reveals different activation energies for each studied phase. This can be correlated to changes in the smectic layer structure that occur between the different smectic phases.
机译：在涵盖各向同性的温度范围内，研究了溶解于手性液晶1-甲基庚基4'-（4-正癸氧基苯甲酰氧基）联苯-4-羧酸酯（10B1M7）中的氙的〜（129）Xe NMR屏蔽和扩散。 I），近晶A（SmA）以及铁电，亚铁电和反铁电近晶C〜*（SmC〜*）相。 〜（129）Xe屏蔽清晰显示I-SmA和SmA-SmC〜*（铁电）相变。 SmC〜*子相变也可以通过较小但可区分的屏蔽位移（伴随线宽变化）来检测。将较早建立的理论模型应用于屏蔽数据，确认了当SmA相形成时对屏蔽的负各向异性贡献，并允许评估SmC〜*中的倾斜角。扩散实验主要是在平行于层法线的方向上进行的，即在近晶相中沿着外部磁场D_（||）进行，而少数实验是在面内方向（即垂直于垂直方向）上进行的。外部磁场D_⊥也是如此。这些实验表明〜（129）Xe扩散张量的大各向异性D_⊥/ D_（||）随着温度降低而增加。将Arrhenius方程应用于D_（||）的温度相关性可揭示每个研究阶段的不同活化能。这可以与在不同近晶相之间发生的近晶层结构的变化相关。

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