Surface-assisted photoalignment of discotic liquid crystals by nonpolarized light irradiation of photo-cross-linkable polymer thin films.
Surface-assisted photoalignment of discotic liquid crystals by nonpolarized light irradiation of photo-cross-linkable polymer thin films.
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DOI：
10.1021/jp065686h
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发表时间：
2007-01
期刊：
影响因子：
--
通讯作者：
S. Furumi;K. Ichimura
中科院分区：
文献类型：
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作者：
S. Furumi;K. Ichimura
在本文中，我们描述了以肉桂酰基部分作为侧链的可光交联聚合物薄膜上盘状液晶（DLC）的表面辅助光取向。用 313 nm 的非偏振紫外光倾斜照射聚合物薄膜，由于其方向选择性光异构化和光二聚作用，导致肉桂酰残基倾斜取向。光照射聚合物薄膜上的 DLC 分子以倾斜混合方式排列。这意味着 DLC 指向矢从基材到 DLC 薄膜表面不断变化，从而最大限度地减少弹性自由能。有趣的是，我们发现排列的 DLC 分子的倾斜方向明显受到含肉桂酸酯聚合物的化学结构的影响。当聚（肉桂酸乙烯酯）薄膜倾斜地暴露于非偏振紫外光时，DLC 向与紫外光传播相反的方向倾斜。与此形成鲜明对比的是，预先倾斜暴露于非偏振紫外光的聚（甲基丙烯酸酯）束缚肉桂酰基的薄膜提供了与光传播平行的倾斜DLC方向。倾斜照射的聚合物薄膜上棒状（棒状）液晶的倾斜取向支持了该结果。 DLC 的这种光取向行为可以通过锚定 DLC 分子与聚合物薄膜的光二聚体以及薄膜界面处肉桂酰基侧链剩余 E 异构体之间的分子间相互作用之间的平衡来合理化。目前的 DLC 光配向技术不仅为理解 DLC 的各向异性物理特性，而且为设计和制造用于光子学和电子学应用的新型纳米器件开辟了有希望的途径。
In this article, we describe the surface-assisted photoalignment of discotic liquid crystals (DLCs) on thin films of photo-cross-linkable polymers with cinnamoyl moieties as the side chains. Oblique irradiation of the polymer thin films with nonpolarized UV light at 313 nm brought about inclined orientation of the cinnamoyl residues as a result of their direction-selective photoisomerization and photodimerization. The DLC molecules on the photoirradiated polymer films were aligned in a tilted hybrid manner. This means that the DLC directors are continuously altered from the substrate to the DLC film surface so as to minimize the elastic free energy. Interestingly, we found that the tilted direction of aligned DLC molecules is clearly influenced by the chemical structures of the cinnamate-containing polymers. When a poly(vinyl cinnamate) thin film was obliquely exposed to nonpolarized UV light, the DLCs were inclined to the direction opposite to the UV light propagation. In a keen contrast, the thin film of poly(methacrylate)s tethering cinnamoyl groups, which was obliquely exposed to nonpolarized UV light in advance, provided the tilting DLC direction in parallel with the light propagation. The results were supported by tilted orientation of calamitic (rod-shaped) liquid crystal on the obliquely irradiated polymer films. Such photoalignment behavior of the DLCs can be rationalized by anchoring balance between intermolecular interaction of the DLC molecules with the photodimers of polymer films and those with the remaining E-isomers of cinnamoyl side chains at the film interface. The present technique of DLC photoalignment opens promising ways not only to understand anisotropic physical properties of DLCs, but also to design and fabricate novel nanodevices for photonics and electronics applications.