An electron resonance investigation of molecular motion in the smectic A mesophase of a liquid crystal
An electron resonance investigation of molecular motion in the smectic A mesophase of a liquid crystal
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液晶近晶 A 中间相分子运动的电子共振研究
DOI：
10.1080/00268977400101511
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发表时间：
1974
影响因子：
1.7
通讯作者：
C. Zannoni
中科院分区：
文献类型：
--
作者：
G. R. Luckhurst;M. Setaka;C. Zannoni
本文报道了溶解在近晶 A 中间相中的自旋探针的电子共振谱的角度依赖性。分析光谱以获得线宽系数的角度变化，从而获得角度线宽系数。这些角系数可以通过采用基于分子重新定向的强碰撞模型的自旋弛豫理论来解释。这样的分析产生关于自旋探针的长轴和短轴重新定向的相关时间的值以及溶质有序参数p4的大小。还探讨了根据基于分子重新取向扩散模型的理论解释角线宽系数的可能性。只有当取向顺序为 hrgh 时（因为处于近晶相），才能从扩散模型中获得这些系数的相对简单的表达式。然后，角线宽系数的分析提供了平行于和垂直于自旋探针长轴的扩散张量分量的值。扩散张量中较大的各向异性可能表明分子绕长轴运动不受阻碍。高度有序系统中分子重新取向的两种模型似乎都对观察到的角线宽系数提供了令人满意的解释。
This paper reports the angular dependence of the electron resonance spectrum of a spin probe dissolved in a smectic A mesophase. The spectra were analysed to obtain the angular variation of the linewidth coefficients and hence the angular linewidth coefficients. These angular coefficients -may be interpreted by employing a theory of spin relaxation based on the strong collision model for molecular reorientation. Such an analysis yields values for the correlation times for reorientation about the long and short axes of the spin probe as well as the magnitude of the solute order parameter p4. The possibility of interpreting the angular linewidth coefficients in terms of a theory based on the diffusion model for molecular reorientation is also explored. Relatively straightforward expressions for these coefficients can only be obtained from the diffusion model when the orientational order is hrgh, as it is in a smectic phase. The analysis of the angular linewidth coefficients then provides values for the components of the diffusion tensor parallel and perpendicular to the long axis of the spin probe. The large anisotropy in the diffusion tensor may be indicative of the unhindered molecular motion about the long axis. Both models of molecular reorientation in a highly ordered system appear to provide a satisfactory account of the observed angular linewidth coefficients.