Abstract
In search for novel nematic materials, a laterally linked H-shaped liquid crystal dimer has been synthesised and characterised. The distinct feature of this material is a very broad temperature range (about 50oC) of the nematic phase, which is in contrast with other reported H-dimers that show predominantly smectic phases. The material exhibits interesting textural features at the scale of nanometers (presence of smectic clusters) and at the macroscopic scales. Namely, at a certain temperature, the flat samples of the material show occurrence of domain walls. These domain walls are caused by the surface anchoring transition and separate regions with differently tilted director. Both above and below this transition temperature, the material represents a uniaxial nematic, as confirmed by the studies of defects in flat samples and samples with colloidal inclusions, freely suspended drops, X-ray diffraction and transmission electron microscopy.
Highlights
Liquid crystals (LCs) with their numerous thermodynamically stable phases present a dramatic illustration of how a small alteration of the molecular structure can lead to profound changes in the long-range order
The N-I transition temperature TNI varies within 1 3o C depending on the cell thickness d and alignment layer; TNI is constant within the entire area of the same cell
The material is a uniaxial nematic with embedded smectic nanoclusters that exist in the entire range of the nematic phase
Summary
Liquid crystals (LCs) with their numerous thermodynamically stable phases present a dramatic illustration of how a small alteration of the molecular structure can lead to profound changes in the long-range order. One of the reasons for the controversy is that uniaxial nematic phase can mimic the features of the Nb phase in a variety of forms Very often this mimicking behavior is rooted in the complexity of surface alignment of molecules with nontrivial shapes such as bent-core [38, 49] and tetrapodes mesogens.[50] An interesting example of mimicking behavior is demonstrated by a mesogen with four lateral flexible chains.[51] The biaxial-like features occur as a result of thermal expansion which triggers flows; the latter cause a biaxial tilt of the uniaxial director that can persist for hours because of high viscosity of the material.[51, 52]. At the scale of nanometers, the material show traces of smectic clustering
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