Institut für Chemie-Physikalische Chemie, Martin-Luther-Universität Halle-Wittenberg, von-Danckelmann-Platz 4, 06120 Halle, Germany.
ACS Nano. 2013 Aug 27;7(8):6627-35. doi: 10.1021/nn400066n. Epub 2013 Jul 15.
Soft self-assembling photonic materials such as cholesteric liquid crystals are attractive due to their multiple unique and useful properties, in particular, an optical band gap that can be continuously and dynamically tuned in response to weak external influences, easy device integration, compatibility with flexible architectures, and, as shown here, potential for submicrometer optical applications. We study such a system formed by a short-pitch cholesteric confined in the core of polymer fibers produced by coaxial electrospinning, showing that the selective reflection arising from the helical photonic structure of the liquid crystal is present even when its confining cavity is well below a micrometer in thickness, allowing as little as just half a turn of the helix to develop. At this scale, small height variations result in a dramatic change in the reflected color, in striking difference to the bulk behavior. These conclusions are made possible by combining focused ion beam (FIB) dissection and imaging of the internal fiber morphology with optical microscopy. The FIB dissection further reveals that the cross section of the cavity within the fiber can have a shape that is quite different from that of the outside fiber. This is critical for the photonic behavior of the composite fiber because different optical textures are generated not only by change in thickness but also by the shape of the cavity. Our results provide insights into the behavior of cholesterics in submicrometer cavities and demonstrate their potential at such dimensions.
软自组装光子材料，如胆甾相液晶，由于其多种独特而有用的性质而受到关注，特别是光学带隙可以对外界弱影响进行连续和动态的调节，易于器件集成，与柔性结构兼容，并且，如这里所示，具有亚微米级光学应用的潜力。我们研究了由短螺距胆甾相限制在同轴电纺聚合物纤维核心中形成的这样一个系统，表明即使其限制腔的厚度远低于一微米，液晶螺旋光子结构引起的选择性反射仍然存在，允许仅半圈螺旋发展。在这个尺度上，小的高度变化会导致反射颜色发生显著变化，与整体行为形成鲜明对比。这些结论是通过结合聚焦离子束（FIB）对纤维内部形态的剖析和成像以及光学显微镜来实现的。FIB 剖析进一步表明，纤维内空腔的横截面可以与外部纤维的形状有很大的不同。这对于复合纤维的光子行为至关重要，因为不仅通过厚度变化而且通过腔的形状产生不同的光学纹理。我们的结果提供了对亚微米腔中胆甾相行为的深入了解，并展示了它们在这种尺寸下的潜力。
