Study of smectic layer liquid crystal formed by rod-like polymers arranged their molecular terminals regularly in space

具有光学活性侧链的聚硅烷呈现棒状构型。当相对分子质量较小时，它们形成清晰的热致胆甾型液晶；当分子量分布较窄时，它们在胆甾型液晶相下形成近晶相，其近晶层间距与聚硅烷的分子长度相对应。在本研究中，我们将两个不同分子量的样品混合在一起，观察近晶层的行为。结果发现，当分子量差较小时，近晶相不稳定，而当分子量差较大时，近晶相分离。此外，我们还通过原子转移自由基聚合法合成了聚苯乙烯(PS)和侧链液晶聚合物(LCP)两嵌段共聚物。PS链段的质量分数为0.22，形成微偏析结构，PS柱面六角堆积在LCP基质中，按升温顺序形成近晶A相、向列相和各向同性相。向列相温度下的剪切流在速度方向上很好地定向了PS微柱和LCP的向列相介元。微柱的取向度为0.95，而向列型液晶的取向序参数约为0.5。有趣的是，向列型液晶介元在各向同性熔体中失去取向有序性后，冷却后恢复其初始取向。这种自发取向表明，取向随温度变化而保持强烈的PS柱体是向列相介元的锚定底物。

Polysilanes having optically active side-chain exhibit rod-like configuration. They forms clear thermotropic-cholesteric liquid crystal when their molecular weights are relatively small, while they show smectic phase under cholesteric liquid crystal phase when molecular weight distribution is narrow (Mw/Mn < 1.1) and their smectic layer distance corresponds to the molecular length of polysilane. In this study, we mixed two samples with different molecular weights to observe behavior of smectic layers. As a result, we found that smectic phase is unstable when difference of the molecular weights is small, while two smectic phase is separated when difference of the molecular weights is large.Additionally, we prepared a diblock copolymer composed of polystyrene (PS) and side-chain liquid crystal polymer (LCP) by atom transfer radical polymerization. The weight fraction of the PS segment is 0.22, resulting in a microsegregated structure with PS cylinders hexagonally packed in a matrix of LCP, which forms smectic A, nematic and isotropic phases in order of increasing temperature. Shear flow at nematic temperatures orients well the PS microcylinders, as well as the nematic mesogens of the LCP in the velocity direction. A high degree of orientation of 0.95 is attained for microcylinders while the orientational order parameter of the nematic LC is around 0.5. Interestingly, the nematic LC mesogens recover their initial orientation upon cooling after they have lost the orientational order in the isotropic melt. This spontaneous orientation shows that PS cylinders whose orientation is strongly sustained with a temperature variation acts as an anchoring substrate for the nematic mesogens.