Anisotropic Dynamics of Benzonitrile Confined in δ and ε Clathrate Phases of Syndiotactic Polystyrene
Anisotropic Dynamics of Benzonitrile Confined in δ and ε Clathrate Phases of Syndiotactic Polystyrene
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DOI：
10.1021/acs.macromol.8b00799
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发表时间：
2018-11-13
期刊：
影响因子：
5.5
通讯作者：
Inoue, Tadashi
中科院分区：
文献类型：
--
作者：
Kobayashi, Hideo;Akazawa, Sho;Inoue, Tadashi
用介电光谱法研究了苯腈（BzCN）在共晶聚苯乙烯（sPS）共晶区的各向异性动力学。特别研究了两种类型的共晶（delta和epsilon笼形物）的晶相取向对介电弛豫行为的影响。无论其取向如何，δ型共晶中BzCN的弛豫时间都比ε型共晶长，表明δ型结构对客体运动的约束程度高于ε型结构。由于客体BzCN弛豫，单轴拉伸处理对Delta和epsilon共晶的介电强度Delta epsilon产生不同的影响：拉伸后Delta共晶的Delta epsilon增大，而epsilon晶体的Delta epsilon减小。这一观察结果可归因于这些共晶腔内客体分子各向异性运动的方向性差异。偶极矩矢量方向对应的BzCN分子轴方向为垂直方向。对于δ共晶，与sPS链轴（c轴）平行，而对于ε共晶，与sPS链轴平行。由于sPS/BzCN薄膜的拉伸使c轴平行于薄膜表面，因此对于δ共晶，BzCN旋转平面的法线方向垂直于施加在样品膜上的电场（厚度方向），对于ε共晶，则平行于电场方向。这样的自转轴对电场的排列导致拉伸后的δ和e共晶的δ分别增加和减少。实验结果表明，通过控制sPS共晶的结构和取向可以改变sPS共晶薄膜的介电性能。
Anisotropic dynamics of benzonitrile (BzCN) confined in the cocrystalline region of syndiotactic polystyrene (sPS) was studied by means of dielectric spectroscopy. Especially examined was the effect of orientation of the crystalline phase for two types of cocrystals, delta and epsilon clathrates, on the dielectric relaxation behavior. The relaxation time of the BzCN in the delta cocrystal, regardless of its orientation, was found to be longer than that in the epsilon cocrystal, indicating that the delta structure has higher degree of constraint on the guest motion than the epsilon structure. With respect to dielectric intensity Delta epsilon due to the guest BzCN relaxation, uniaxial stretching treatment caused different effects in the delta and epsilon cocrystals: Delta epsilon increased for the delta cocrystal and decreased for the epsilon crystal by stretching. This observation was attributable to the difference in directionality of anisotropic motion of the guest molecule inside the cavities of these cocrystals. The preferable orientation of the molecular axis of BzCN corresponding to the vector direction of the dipole moment was perpendicular. to the sPS chain axis (c-axis) for the delta cocrystal, whereas it was parallel to that for the epsilon cocrystal. Since the stretching of the sPS/BzCN film made the c-axis align parallel to the film surface, the normal direction of the rotation plane of BzCN was set perpendicular to the electric field imposed on the sample films (to the thickness direction) for the delta cocrystal and parallel to it for the epsilon cocrystal. Such arrangements of the rotation axis to the electric field resulted in the increase and the decrease in Delta epsilon for the stretched delta and e cocrystals, respectively. The experimental findings indicated the possibility that the dielectric properties of sPS cocrystal films could be changed by controlling the structure and crystallite orientation of sPS cocrystals.