Morphology design in 2D confinement


Liquid crystals

The intrinsic anisotropy of one-dimensional nanostructures and microstructures offers the opportunity to generate uniformly oriented supramolecular architectures. We are investigating the formation of mesophases consisting of liquid-crystalline functional materials inside nanopores, which yields nanowires with a pronounced liquid-crystalline texture (Fig. 1). Nanowires containing columns of discotic (disk-shaped) molecules aligned with their long axes might be used as nanocables, as charge carriers have an extraordinarily high mobility along the columns.


 Figure 1. Liquid-crystalline nanowires.



More complex architectures such as polymer/liquid crystal composite nanotubes are accessible (Fig. 2). For example, an inner liquid-crystalline layer can be surrounded by an outer layer consisting of a commodity polymer. In Fig.2, the liquid-crystalline layer was selectively stained with heavy metal atoms and therefore appears dark.


Figure 2. Transmission electron micrograph of a polymer/liquid crystal composite nanotube. An outer layer consisting of a commodity polymer surrounds an inner liquid-crystalline layer. The latter was selectively stained with heavy metal atoms and therefore appears dark.



The orientation of the mesophase inside the pores can be probed by X-ray diffraction (Fig. 3). The occurrence of specific reflections in the X-ray pattern is related to the presence of columns with a specific orientation. Advanced texture analysis reveals orientation distributions.


Figure 3. Schematic diagram of a typical set-up used for X-ray diffraction on aligned liquid-crystalline nanorods inside porous templates in the reflection mode. As example, a columnar mesophase is shown, where reflections originate from the intermolecular distance within the columns and from the intercolumnar distance. Depending on the orientation of the columns, specific reflections appear in the XRD patterns.



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