Department of Solid State Physics, Jozef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia.
J Phys Chem B. 2010 Sep 23;114(37):11993-2001. doi: 10.1021/jp105211q.
The molecular dynamics of a chiral liquid crystal showing a rich variety of frustrated mesophases has been investigated by means of 1H NMR relaxometry. The interest in this lactate derivative, HZL 7/, is related to a large range of thermal stabilities of the twist grain boundary (TGB) phases. Dispersions of the 1H spin-lattice relaxation times, T1, in the frequency range from 300 MHz to 5 kHz were measured and consistently analyzed in the isotropic, chiral nematic, TGBA, and two TGBC* phases. In the isotropic and N* phases, a three-exponential magnetization decay was observed and assigned to three specific molecular groups of the HZL 7/* (molecular core, methyl, and methylene groups). In the TGB phases, all T1 components merge into a single one. The analysis of the T1 dispersion in the TGBA* phase shows that the translational self-diffusion relaxation mechanism dominates over a broad frequency range and that layer undulations are less relevant than the relaxation contribution associated with the diffusion process across the TGB structure. In the TGBC1* phase, the T1 dispersion presents a strong contribution of in-layer tilt direction fluctuations (T1(-1) proportional to ν(-1/2)), while, in the TGBC2* phase, the linear frequency dependence of T1 could be associated with a much stronger contribution of layer undulations than for the other TGB phases. This is at present the first molecular dynamics investigation on several TGB phases by means of 1H NMR relaxometry.
通过 1H NMR 弛豫测量研究了一种手性液晶的分子动力学，该液晶表现出丰富多样的受挫中间相。对这种乳酸酯衍生物 HZL 7/的研究兴趣与扭曲 grain boundary（TGB）相的大范围热稳定性有关。在 300 MHz 至 5 kHz 的频率范围内测量了 1H 自旋晶格弛豫时间 T1 的分散，并在各向同性、手性向列相、TGBA和两个 TGBC相中进行了一致的分析。在手性向列相和 N相中，观察到三指数磁化衰减，并将其分配给 HZL 7/的三个特定分子基团（分子核心、甲基和亚甲基基团）。在 TGB 相中，所有 T1 分量合并为一个分量。在 TGBA相中 T1 分散的分析表明，在宽频率范围内，平移自扩散弛豫机制占主导地位，层起伏的相关性不如与 TGB 结构扩散过程相关的弛豫贡献。在手性向列相 TGBC1中，T1 分散呈现出较强的层内倾斜方向波动贡献（T1(-1)正比于 ν(-1/2)），而在手性向列相 TGBC2中，T1 的线性频率依赖性可能与层起伏的贡献比其他 TGB 相更强有关。这是目前通过 1H NMR 弛豫测量对手性向列相进行的首次分子动力学研究。
