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Deuteron NMR Relaxometry Applied to Confined Liquid Crystals

机译:氘核NMR弛豫法应用于受限液晶

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摘要

We discuss the capability of deuteron nuclear magnetic resonance (NMR) spectroscopy and relaxometry to reveal molecular ordering and dynamics in confined liquid crystals. The attention is focused on the high-temperature phase above the nematic-isotropic transition, which is - in the absence of the long-range orientational order - very suitable for the study of surface interactions. Deuteron NMR spectra and relaxation rates are presented for two representatives of confined liquid-crystal systems: 8CB in cylindrical cavities of Anopore membranes and 5CB with an embedded polymer network. A substantial increase in the transverse spin relaxation rate, stimulated by the surface-induced order in enclosures, has been observed. In cylindrical cavities, it exhibits a strong temperature dependence on approaching the phase transition, whereas in the polymer network dispersion it is temperature-independent. The incrcase of T_2~(-1) provides information on the effect of spatial constraints on molecular mobility and on the surface orientational order parameter. Using deuteron relaxometry, one can measure the degree of orientational order in the isotropic phase not only in cylindrical but also in spherical cavities and enclosures of irregular shape, where the standard approach based on quadrupolar splitting of the NMR spectrum fails.
机译:我们讨论氘核核磁共振(NMR)光谱和弛豫法的能力,以揭示受限液晶中的分子有序性和动力学。注意力集中在向列-各向同性转变以上的高温阶段,在没有长距离取向顺序的情况下,该阶段非常适合表面相互作用的研究。给出了受限液晶系统的两个代表的氘核NMR谱图和弛豫速率:Anopore膜圆柱腔中的8CB和具有嵌入式聚合物网络的5CB。观察到在外壳中由表面诱导的顺序刺激的横向自旋弛豫速率大大增加。在圆柱型腔中,它对接近相变表现出强烈的温度依赖性,而在聚合物网络分散液中,它与温度无关。 T_2〜(-1)的递增形式提供了有关空间约束对分子迁移率和表面取向顺序参数的影响的信息。使用氘核弛豫法,不仅可以测量圆柱状的各向同性相的取向度,而且还可以测量球形腔和不规则形状的封闭物的取向顺序,而基于NMR谱的四极分裂的标准方法却失败了。

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