Temperature dependence of the density of some liquid crystals in the alkyl cyanobiphenyl series
TL;DR: In this paper, experimental results for the temperature dependence of the density of propyl- cyanobiphenyl (3CB), butyl - cyanobinphoenyl (4CB), and hexyl-cyanobiphexyl (6CB) are presented.
Abstract: Experimental results for the temperature dependence of the density of propyl – cyanobiphenyl (3CB), butyl – cyanobiphenyl (4CB) and hexyl – cyanobiphenyl (6CB) are presented. The results are compared with previous results for temperature dependence of other members of the alkyl cyanobiphenyl series (nCB). The deviation of the density from linear temperature dependence is discussed in terms of the recently discovered corresponding rule for nematic liquid crystals. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
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TL;DR: The liquid crystal dimer 1ʺ,7ʺ-bis (4-cyanobiphenyl-4ʹ-yl) heptane (CB7CB) has been shown to possess a nematic-nematic phase transition at 376 K as mentioned in this paper.
Abstract: The liquid crystal dimer 1ʺ,7ʺ-bis(4-cyanobiphenyl-4ʹ-yl) heptane (CB7CB) has been shown to possess a nematic–nematic phase transition at 376 K. The phase below this temperature has been identified...
61 citations
Cites background or methods from "Temperature dependence of the densi..."
...Equation (2) describes very well the density of, for example, the ubiquitous 5CB.[28] The temperature dependence of the orientational order parameter S(T) is modelled by the Haller function [29]...
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...86 × 10 K.[28] It is possible that the factor τ is different from zero, meaning that there is a direct temperature effect on the isotropic shielding constant due to the deformation of the xenon electron cloud by neighbouring molecules....
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TL;DR: Transmission electron microscopy of photopolymerized blue phases with controlled lattice plane orientations shows that TEM observation of alignment-controlled, photopolymersized liquid crystals can be a powerful tool to investigate complex liquid crystalline order.
Abstract: Cholesteric blue phases are liquid crystalline phases in which the constituent rod-like molecules spontaneously form three-dimensional, helical structures. Despite theoretical predictions that they are composed of cylindrical substructures within which the liquid crystal molecules are doubly twisted, real space observation of the arrangement of such structures had not been performed. Through transmission electron microscopy of photopolymerized blue phases with controlled lattice plane orientations, we report real space observation and comparison of the lattice structures of blue phases I and II. The two systems show distinctly different contrasts, reflecting the theoretically predicted, body centred and simple cubic arrangement of the double-twist cylinders. Transmission electron microscopy also reveals different tendencies of the two blue phases to align on unidirectionally rubbed surfaces. We thus show that TEM observation of alignment-controlled, photopolymerized liquid crystals can be a powerful tool to investigate complex liquid crystalline order.
58 citations
TL;DR: In this article, a density functional theory (DFT) method was used for the analysis of the photosensitivity of liquid crystalline alkyl cyanobiphenyl (nCB) dimers.
Abstract: In this paper, the photosensitivity of liquid crystalline alkyl cyanobiphenyl (nCB: n = 6, 7; n is the number of carbon atoms in the alkyl chain) dimers has been presented through density functional theory (DFT) calculations. The nCB structures have been optimized using the Becke, three-parameter, Lee–Yang–Parr hybrid functional with the 6-31+G (d) basis set using the crystallographic geometry as input. The electronic structures of the dimer molecules have been computed using the optimized geometries. The spectra of the dimer molecules have been calculated by employing the DFT method. The excited states have been calculated via configuration interaction singles with the semi-empirical Hamiltonian Zerner intermediate neglect of differential overlap. The influence of molecular interactions and the end chain length on ultraviolet absorption spectral characteristics and the photosensitivity of the compounds has been discussed. These results offer a hint for the protection of various optical devices from the i...
20 citations
Cites background from "Temperature dependence of the densi..."
...Alkyl cyanobiphenyl series have been extensively studied by the different research groups using the various computational [1–3] and experimental techniques.[4,5] Particularly, from the scientific viewpoint, and from the practical perspective of LC devices, an...
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TL;DR: It is suggested that for each nCB a unique, characteristic minimal value of ΔT, associated with the I-N-SmA triple point, exists and can be hidden in the negative pressures domain for 'shorter' nCBs, and the possibility of the extension of the 'melting curve' into thenegative pressures region as well as the appearance of the'melting inversion' at high enough pressures is indicated.
Abstract: Results of the extended Landau?de Gennes model analysis and experimental studies of the isotropic?nematic (I?N) and isotropic?smectic-A (I?SmA) phase transitions in rod-like liquid crystalline n-alkylcyanobiphenyls are presented. Experiments were carried out as a function of temperature and pressure using the static dielectric permittivity and its ?nonlinear? (strong electric field related) counterpart?the low-frequency nonlinear dielectric effect. Precise estimations of the values of the discontinuity of the isotropic?mesophase transitions (?T) for nCB from n?=?3?14 have been obtained. It is suggested that for each nCB a unique, characteristic minimal value of ?T, associated with the I?N?SmA triple point, exists. For ?shorter? nCBs it can be hidden in the negative pressures domain. The possibility of the extension of the ?melting curve? into the negative pressures region as well as the appearance of the ?melting inversion? at high enough pressures is indicated.
19 citations
TL;DR: In this paper, the authors conducted dielectric and viscoelastic relaxation measurements for polystyrene (PS)/4-pentyl-4′-cyanobiphenyl (5CB) and PS/4- pentyl- 4′-cyclanoterphenyl(5CT) mixtures in the miscible state with the weight fractions of 5CB or 5CT from 0.04 to 0.27.
Abstract: We conducted dielectric and viscoelastic relaxation measurements for polystyrene (PS)/4-pentyl-4′-cyanobiphenyl (5CB) and PS/4-pentyl-4′′-cyanoterphenyl (5CT) mixtures in the miscible state with the weight fractions of 5CB or 5CT from 0.04 to 0.27 to examine the relationship between two-component dynamics in the mixture. Dielectric relaxation measurements mainly probed the dynamics of low-mass molecule (LM), 5CB or 5CT, because of the much larger dipole moment of LMs compared to that of PS. PS/5CB mixtures exhibited bimodal dielectric relaxation, while PS/5CT showed unimodal relaxation. The observed two relaxation modes (slow and fast modes) in PS/5CB were attributed to the full rotational motion and partial rotational motion of 5CB, respectively. The latter motion is allowed in the restricted space surrounded by less mobile PS matrix. In the case of 5CT, the fast mode was suppressed due to the larger size of 5CT molecule, and only the slow mode (rotational mode) appeared. The relaxation times of slow mod...
16 citations
References
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IBM1
498 citations
TL;DR: In this paper, a simple phenomenological theory is outlined, based on the hypothesis that this excess order resides solely in the degree of alignment of the molecules, the conventional nematic order parameter being larger near the surface than in the bulk.
Abstract: The surface tension γ has been measured for two cyanobiphenyls (5CB and 8CB) at temperatures near the nematic-isotropic transition temperature T c, using the Wilhelmy plate method. Reproducible results were obtained, but only by the exercise of considerable patience: for reasons that are discussed at the end of the paper, it took up to four days for equilibrium to be re-established whenever the temperature was changed. The results suggest that in both materials the equilibrium value of γ increases discontinuously (by approximately 0·3 dyne cm−1) on heating through T c, and that (dγ/dT) is positive both for the isotropic phase just above T c and for the nematic phase just below it. A positive value of (dγ/dT) implies excess order in the surface layers. A simple phenomenological theory is outlined, based on the hypothesis that this excess order resides solely in the degree of alignment of the molecules, the conventional nematic order parameter being larger near the surface than in the bulk. The pre...
126 citations
TL;DR: The density of 8CB has been measured between 28 and 5O°C and the volume change at the SA-N and N-I transitions determined The SA appears to be first order as discussed by the authors.
Abstract: The density of 8CB has been measured between 28 and 5O°C and the volume change at the SA-N and N-I transitions determined The SA-N appears to be first order The implications of the results are discussed with respect to the molecular packing in the unusual structure of the cyanobiphenyls in which the layer spacing is about 14 times the molecular length
109 citations
20 May 2003
TL;DR: In this article, the effect of aberrations on photo-aligned cells is discussed. But the application of photo alignment technologies is not addressed in this paper, as shown in Figure 1.
Abstract: OPTICAL PROPERTIES AND APPLICATIONS OF FERROELECTRIC AND ANTIFERROELECTRIC LIQUID CRYSTALS E.E. Kriezis, L.A. Parry-Jones, and S.J. Elston Introduction Material properties Alignment Optical properties of smectic structures Interaction with electric fields Displays Non-display applications ELECTRO HOLOGRAPHY AND ACTIVE OPTICS N. Hashimoto Electro holography Active optics Conclusions ON THE USE OF LIQUID CRYSTALS FOR ADAPTIVE OPTICS S.R. Restaino Introduction Adaptive optics: definition and history Image formation: basic principles The effect of aberrations Active and adaptive optics Characterization and control of nematic LC devices Wavefront sensing techniques Conclusions POLYMER DISPERSED LIQUID CRYSTALS F. Bloisi and L.R.M. Vicari Introduction PDLC preparation techniques The physics involved in PDLCs PDLC electro-optical behavior Applications of PDLCs NEW DEVELOPMENTS IN PHOTO-ALIGNING AND PHOTO-PATTERNING TECHNOLOGIES: PHYSICS AND APPLICATIONS V.G. Chigrinov, V.M. Kozenkov, and H.S. Kwok Introduction Mechanisms of LC photo-alignment LC surface interaction in photo-aligned cell Applications of photo-alignment technologies New developments Conclusions INDUSTRIAL AND ENGINEERING ASPECTS OF LC APPLICATIONS T. Sonehara Practical spatial modulation Spatial addressing technologies Amplitude modulation and applications Phase modulation and applications Scattering and deflection modulation
88 citations