Department of Chemistry, Faculty of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8571, Japan.
J Phys Chem B. 2012 Aug 2;116(30):9255-60. doi: 10.1021/jp303972s. Epub 2012 Jul 17.
To confirm the molten state of the alkyl chain in soft crystalline phase, smectic E (SmE) phase, thermodynamic and spectroscopic analyses were performed on 4-n-alkyl-4'-isothiocyanatobiphenyl (nTCB, n: the number of carbon atoms in the alkyl group). DSC results of 11TCB and 12TCB, having extra smectic A phase besides smectic E phase, show that their chain-length dependence of entropies of transition (Δ(trs)S) from the ordered crystalline (OC) phase to the SmE phase matches the trend found for nTCB (n = 4-10), while no chain-length dependence is observed in Δ(trs)S at the SmE-to-SmA and SmA-to-isotropic liquid (IL) phase transitions in 11TCB and 12TCB. Temperature dependences of FT-IR spectra of six compounds (n = 2, 3, 5, 8, 10, and 12) were recorded. The CH stretching modes of the chain exhibited more pronounced change at the transition from the OC to the SmE phase than at the transition from the SmE phase to the IL or SmA phase. These results indicate that the alkyl chain is molten in the SmE phase as in IL. The disordering process of nTCB molecules from the OC to IL via anisotropic mesophases is discussed in terms of entropy.
为了确认软结晶相中烷基链的熔融状态，对 4-n-正烷基-4'-异硫氰酸基联苯（nTCB，n：烷基链中碳原子的数量）进行了热力学和光谱分析。除了 SmE 相之外，还具有额外的 SmA 相的 11TCB 和 12TCB 的 DSC 结果表明，它们从有序晶相（OC）到 SmE 相的转变熵（Δ(trs)S）的链长依赖性与 nTCB（n = 4-10）的趋势相匹配，而在 11TCB 和 12TCB 中，SmE 到 SmA 和 SmA 到各向同性液相（IL）的转变中，Δ(trs)S 没有链长依赖性。记录了六种化合物（n = 2、3、5、8、10 和 12）的傅里叶变换红外光谱的温度依赖性。链的 CH 伸缩模式在从 OC 到 SmE 相的转变中比在从 SmE 相到 IL 或 SmA 相的转变中表现出更明显的变化。这些结果表明，烷基链在 SmE 相和 IL 中都是熔融的。根据熵讨论了 nTCB 分子从 OC 到 IL 通过各向异性中间相的无序过程。
