Zorn Matthias, Tahir Muhammad Nawaz, Bergmann Björn, Tremel Wolfgang, Grigoriadis Chris, Floudas George, Zentel Rudolf
Institute for Organic Chemistry, Johannes Gutenberg University, Duesbergweg 10-14, 55128, Mainz, Germany.
Macromol Rapid Commun. 2010 Jun 16;31(12):1101-7. doi: 10.1002/marc.201000049. Epub 2010 May 18.
ZnO nanorod polymer hybrids (i.e., ZnO nanorods coated with a block copolymer with a short anchor block (dopamine) and a longer solubilizing block of polystyrene (PS)) form liquid crystalline (LC) phases if they are dispersed at high concentration e.g., in a PS oligomer matrix. Due to the high mobility of the low T(g) -matrix the nanorod polymer hybrids show a switching behavior under an applied AC electric field. Hence, the orientation of the nanorod mesogens can be changed from planar (parallel to the substrate) to homeotropic (perpendicular) in full analogy to the switching of low molecular liquid crystals in an electric field. Dielectric measurements show that such a switching is mainly due to the cooperative LC behavior, because the rods themselves exhibit only a very small effective dipole moment. The process can be investigated by polarizing microscopy. SEM images show the orientations of the individual nanorods, which correspond to the Fredericks transition well known for liquid crystals aligned in an electric field. This was the first time such a transition could be visualized by electron microscopy due to the large nanorod mesogens. The observation is interesting to orient nanorods perpendicular to an electrode and can help to improve optoelectronic devices.
氧化锌纳米棒聚合物杂化物（即涂覆有具有短锚定嵌段（多巴胺）和较长聚苯乙烯（PS）增溶嵌段的嵌段共聚物的氧化锌纳米棒）如果以高浓度分散，例如在PS低聚物基质中，就会形成液晶（LC）相。由于低玻璃化转变温度（T(g)）基质的高流动性，纳米棒聚合物杂化物在施加的交流电场下表现出开关行为。因此，纳米棒液晶元的取向可以从平面（平行于基板）变为垂直排列（垂直），这与电场中低分子液晶的开关完全类似。介电测量表明，这种开关主要归因于协同液晶行为，因为棒本身仅表现出非常小的有效偶极矩。该过程可以通过偏光显微镜进行研究。扫描电子显微镜（SEM）图像显示了各个纳米棒的取向，这与电场中排列的液晶中熟知的弗雷德里克斯转变相对应。由于纳米棒液晶元较大，这是首次通过电子显微镜观察到这种转变。该观察结果对于使纳米棒垂直于电极取向很有意义，并且有助于改进光电器件。
