Abstract
The synthesis and characterisation of the nonsymmetric liquid crystal dimer, 1-(4-cyanobiphenyl-4'-yloxy)-6-(4-cyanobiphenyl-4'-yl) hexane (CB6OCB) is reported. An enantiotropic nematic (N)-twist-bend nematic (NTB) phase transition is observed at 109˚C and a nematic-isotropic phase transition at 153˚C. The NTB phase assignment has been confirmed using polarised light microscopy, freeze fracture transmission electron microscopy (FFTEM), 2H-NMR spectroscopy, and X-ray diffraction. The effective molecular length in both the NTB and N phases indicates a locally intercalated arrangement of the molecules, and the helicoidal pitch length in the NTB phase is estimated to be 8.9 nm. The surface anchoring properties of CB6OCB on a number of aligning layers is reported. A Landau model is applied to describe high-resolution heat capacity measurements in the vicinity of the NTB-N phase transition. Both the theory and heat capacity measurements agree with a very weak first-order phase transition. A complementary extended molecular field theory was found to be in suggestive accord with the 2H-NMR studies of CB6OCB-d2, and those already known for CB7CB-d4. These include the reduced transition temperature, TNTBN/TNI, the order parameter of the mesogenic arms in the N phase close to the NTB-N transition, and the order parameter with respect to the helix axis which is related to the conical angle for the NTB phase.
Original language | English |
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Pages (from-to) | 6827-6840 |
Number of pages | 14 |
Journal | Soft matter |
Volume | 12 |
Issue number | 32 |
Early online date | 11 Jul 2016 |
DOIs | |
Publication status | Published - 2016 |
Bibliographical note
AcknowledgementsThe FFTEM data were obtained at the (Cryo) TEM facility at the
Liquid Crystal Institute, Kent State University, supported by the
Ohio Research Scholars Program Research Cluster on Surfaces
in Advanced Materials. ODL acknowledges the support of NSF
DMR-1410378 grant. The authors are grateful for financial
support from MINECO/FEDER MAT2015-66208-C3-2-P and from
the Gobierno Vasco (GI/IT-449-10)
OA via RSC Gold4Gold