The investigation of dimeric materials with a nematic

The investigation of dimeric materials with a nematic – nematic phase
Z. Ahmed*, C. Welch, E. Al-Luhaybi, M.-G. Tamba, A. Kohlmeier1, G. H. Mehl
Department of Chemistry, University of Hull, Hull HU6 7RX, UK
Several hydrocarbon linked mesogenic dimers are known to exhibit an additional nematic phase (Nx)
below a conventional uniaxial nematic phase (N). The correlation between molecular structure and the
nematic - nematic phase transitions (N- Nx/Ntb) is not yet well understood. Nematic-nematic transitions
are in thermotropic liquid crystals associated in most cases with the formation of a columnar structure in
the low temperature nematic phase [1,2,3] or the onset of cluster formation [4] or with folding processes of
polymer chains,[5] there is evidence too for the formation of the twist-bend structures [6,7] as well as the
formation of domain assemblies.[8]
The synthesis of a range of such dimeric materials, symmetric as well non-symmetric systems with both
positive and negative dielectric anisotropy, containing linear and bent structures in the aromatic core
systems will be presented. The characterisation of these systems by the use of differential scanning
calorimetry (DSC), optical polarizing microscopy (OPM) and X-ray diffraction (XRD) studies will be
described in detail and the results for these systems will be compared and structure properties
relationships and the impact on the formation of nematic-nematic transitions will be discussed.
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* presenting author; E-mail: