Journal ArticleDOI
Dielectric, calorimetric and mesophase properties of 1′′-(2′,4-difluorobiphenyl-4′-yloxy)-9′′-(4-cyanobiphenyl-4′-yloxy) nonane: an odd liquid crystal dimer with a monotropic mesophase having the characteristics of a twist-bend nematic phase
Nerea Sebastián,David López,Beatriz Robles-Hernández,Beatriz Robles-Hernández,M. R. de la Fuente,Josep Salud,M. A. Perez-Jubindo,D. A. Dunmur,Geoffrey R. Luckhurst,D. J. B. Jackson +9 more
TLDR
It is concluded that the low temperature mesophase exhibits the characteristics of a twist-bend nematic phase, and the nematic-to-isotropic phase transition has been exhaustively studied from the accurate evolution of the heat capacity and the static dielectric permittivity data.Abstract:
This paper reports a novel liquid crystal phase having the characteristics of a twist-bend nematic phase formed by a non-symmetric ether-linked liquid crystal dimer. The dimer 1''-(2',4-difluorobiphenyl-4'-yloxy)-9''-(4-cyanobiphenyl-4'-yloxy) nonane (FFO9OCB) exhibits two liquid-crystalline phases on cooling at a sufficiently high rate from the isotropic phase. The high temperature mesophase has been reported in the literature as nematic and confirmed in this study. The other mesophase is metastable and can be supercooled giving rise to a glassy state. Its identification and characterization are based on optical textures, broadband dielectric spectroscopy, calorimetry, measurements of both splay and bend elastic constants in the nematic phase and miscibility studies. It is concluded that the low temperature mesophase exhibits the characteristics of a twist-bend nematic phase. Dielectric measurements enable us to obtain the static permittivity and information about the molecular dynamics in the isotropic phase, in the nematic mesophase and across the isotropic-to-nematic phase transition. Two orientations, parallel and perpendicular to the director, have been investigated. In the high temperature nematic mesophase, the dielectric anisotropy is found to be positive. Measurements of the parallel component of the dielectric permittivity are well-explained by the molecular theory of dielectric relaxation in nematic dimers (M. Stocchero, A. Ferrarini, G. J. Moro, D. A. Dunmur and G. R. Luckhurst, J. Chem. Phys., 2004, 121, 8079). The dimer is modelled as a mixture of cis and trans conformers and the model allows an estimate of their relative populations at each temperature. The nematic-to-isotropic phase transition has been exhaustively studied from the accurate evolution of the heat capacity and the static dielectric permittivity data. It has been concluded that the transition is first order in nature, but close to tricritical. The nature of the nematic-to-the novel liquid crystal phase transition is difficult to analyze to the same extent because of insufficient precision. Only observations at cooling rates of 10 K min(-1) or higher were possible because on heating from the glassy state, the twist-bend nematic mesophase crystallizes at temperatures far below the nematic-nematic phase transition.read more
Citations
More filters
Journal ArticleDOI
Understanding the twist-bend nematic phase: the characterisation of 1-(4-cyanobiphenyl-4′-yloxy)-6-(4-cyanobiphenyl-4′-yl)hexane (CB6OCB) and comparison with CB7CB
Daniel A. Paterson,Min Gao,Young-Ki Kim,Afsoon Jamali,Kirsten L. Finley,Beatriz Robles-Hernández,S. Diez-Berart,Josep Salud,M. Rosario de la Fuente,Bakir A. Timimi,Herbert Zimmermann,Cristina Greco,Alberta Ferrarini,John Storey,David López,Oleg D. Lavrentovich,Geoffrey R. Luckhurst,Corrie T. Imrie +17 more
TL;DR: A complementary extended molecular field theory was found to be in suggestive accord with the (2)H-NMR studies of CB6OCB-d2, and those already known for CB7CB-d4, including the reduced transition temperature, TNTBN/TNI, and the order parameter of the mesogenic arms in the N phase close to the NTB-N transition.
Journal ArticleDOI
Reversible Isothermal Twist–Bend Nematic–Nematic Phase Transition Driven by the Photoisomerization of an Azobenzene-Based Nonsymmetric Liquid Crystal Dimer
Daniel A. Paterson,Daniel A. Paterson,Jie Xiang,Gautam Singh,Rebecca Walker,Dena Mae Agra-Kooijman,Alfonso Martinez-Felipe,Min Gao,John Storey,Satyendra Kumar,Oleg D. Lavrentovich,Corrie T. Imrie +11 more
TL;DR: The dramatic changes in TNTBN provide evidence that the transition between the normal nematic and twist-bend nematic with spontaneous breaking of chiral symmetry is crucially dependent on the shape of molecular dimers, which changes greatly during the trans-cis isomerization.
Journal ArticleDOI
Cyanobiphenyl-based liquid crystal dimers and the twist-bend nematic phase
TL;DR: In this paper, the synthesis and characterisation of several members of the 1,ω-bis(4-cyanobiphenyl-4′-yl) alkane (CBnCB) homologous series are reported.
Journal ArticleDOI
Physics of liquid crystals of bent-shaped molecules
Journal ArticleDOI
Molecular geometry, twist-bend nematic phase and unconventional elasticity: a generalised Maier–Saupe theory
TL;DR: Here, using a major extension of the Maier-Saupe molecular field theory, the transition from the nematic (N) to the NTB phase is described, and it is shown that on approaching the transition there is a gradual softening of the bend mode in the N phase.
References
More filters
Journal ArticleDOI
Liquid crystal ‘blue phases’ with a wide temperature range
TL;DR: It is proposed that the unusual behaviour of these blue phase materials is due to their dimeric molecular structure and their very high flexoelectric coefficients, which sets out new theoretical challenges and potentially opens up new photonic applications.
Journal ArticleDOI
Nematic twist-bend phase with nanoscale modulation of molecular orientation
Volodymyr Borshch,Young-Ki Kim,Jie Xiang,Min Gao,Antal Jakli,Vitaly P. Panov,Jagdish K. Vij,Corrie T. Imrie,Maria-Gabriela Tamba,Georg H. Mehl,Oleg D. Lavrentovich +10 more
TL;DR: This work experimentally demonstrates a new nematic order, formed by achiral molecules, in which the director follows an oblique helicoid, maintaining a constant oblique angle with the helix axis and experiencing twist and bend.
Journal ArticleDOI
Phase behavior and properties of the liquid-crystal dimer 1′′,7′′-bis(4-cyanobiphenyl-4′-yl) heptane: A twist-bend nematic liquid crystal
Mirko Cestari,Mirko Cestari,S. Diez-Berart,D. A. Dunmur,Alberta Ferrarini,M. R. de la Fuente,D. J. B. Jackson,David López,Geoffrey R. Luckhurst,M. A. Perez-Jubindo,Robert M. Richardson,Josep Salud,Bakir A. Timimi,Herbert Zimmermann +13 more
TL;DR: It is concluded that the low-temperature mesophase of CB7CB is a new type of uniaxial nematic phase having a nonuniform director distribution composed of twist-bend deformations, and calculations using an atomistic model and the surface interaction potential with Monte Carlo sampling predict dielectric and elastic properties in the nematics phase.
Book
Critical phenomena in liquids and liquid crystals
TL;DR: In this article, critical scattering theory and critical phenomena in alloys magnets and superconductors are discussed. But the critical thinking series phenomena answer guide is not included in this paper.
Journal ArticleDOI
Liquid crystal dimers and higher oligomers: between monomers and polymers
TL;DR: The underlying theme of this Critical Review is the relationship between molecular structure and liquid crystalline behaviour in a class of materials referred to as liquid crystal oligomers, and how this molecular architecture has been exploited to address issues in a range of quite different areas and has given rise to potential applications for these materials.