Photoinduced nanoscale cooperative motion in a well-defined triblock copolymer.
Photoinduced nanoscale cooperative motion in a well-defined triblock copolymer.
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DOI：
10.1002/smll.200600724
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发表时间：
2007-05
期刊：
影响因子：
13.3
通讯作者：
Haifeng Yu;S. Asaoka;A. Shishido;T. Iyoda;T. Ikeda
中科院分区：
文献类型：
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作者：
Haifeng Yu;S. Asaoka;A. Shishido;T. Iyoda;T. Ikeda
偶氮苯部分（AZ）可以通过重复的trans-cis-trans异构化循环被光调制到有序状态，其偶极跃迁矩几乎垂直于光化光的偏振方向。[1]伴随着这样的排列，光惰性介晶与AZ一起由于分子协同运动（MCM）而经历取向，这已经被广泛探索以分别控制低分子量化合物、液晶（LC）共聚物和交联LC凝胶中的介晶排列、折射率变化和光机械能量转换。[1-3]MCM的一个重要应用是全息光存储。[1，3]为了获得大数据容量，需要基于布拉格型光栅的容量存储，其需要厚（几百微米）和透明的膜作为记录介质。由于AZ的大摩尔消光系数（> 104 L摩尔/cm 2 - 1），已经尝试用光惰性介晶稀释它们作为改善膜的透明度的方法。[3]然而，介晶聚集体对可见光的散射阻止了实现具有100%衍射效率的光栅。嵌段共聚物可以通过微相分离自组装形成有序的周期性纳米结构，如球形、圆柱形、双螺旋形和层状结构，[4]这些结构可以作为模板或支架来制备纳米材料。[5，6]有趣的是，这样的纳米结构在纳米纤维和纳米孔的制备中为反应提供了良好的基底，例如交联、降解或水解。[6]然而，在纳米尺度域的光诱导MCM从来没有被研究过，虽然引入的AZ到嵌段共聚物的设计的微相分离材料给出了一些有趣的现象。[7-9]限制光触发MCM的纳米尺度
Azobenzene moieties (AZs) can be photomodulated to an ordered state with their dipole transition moments almost perpendicular to the polarization direction of actinic light by repetition of the trans–cis–trans isomerization cycles.[1] Accompanying such alignment, photoinert mesogens undergo orientation together with the AZs due to molecular cooperative motion (MCM), which has been extensively explored to control mesogen alignment, change in refractive index, and photomechanical energy transformation in lowmolecular-weight compounds, liquid-crystalline (LC) copolymers, and crosslinked LC gels, respectively.[1–3] One of the most important applications of the MCM is holographic optical storage.[1, 3] To obtain large data capacities, volume storage is required based on Bragg-type gratings, which needs thick (several hundred micrometers) and transparent films as recording media. As a result of the large molar extinction coefficient of AZs (> 104 L molÀ1 cmÀ1), diluting them with photoinert mesogens has been tried as a method to improve the transparency of the film.[3] However, the scattering of visible light by mesogenic aggregates prevents gratings with 100% diffraction efficiency from being ACHTUNGTRENNUNGachieved. Confining the mesogenic domains to the nanoscale might be one of the best methods to avoid the scattering.Generally, block copolymers can self-assemble by microphase separation into ordered periodic nanostructures, such as spheres, cylinders, double gyroids, and lamellae,[4] which have been used as templates or scaffolds to prepare nanomaterials.[5, 6] Interestingly, such nanostructures provide a good substrate for reactions, such as crosslinking, degradation, or hydrolysis, in the preparation of nanofibers and nanopores.[6] However, photoinduced MCM in the nanoscale domain has never been studied, although introduction of the AZs into block copolymers has given the designed microphase-separated materials some interesting phenomena.[7–9] Restricting the phototriggered MCM in nanoscale