Orientational order of 1,3-dichloro-2-ethenylbenzene in liquid-crystal solvents

1997 ◽  
Vol 75 (8) ◽  
pp. 1156-1161 ◽  
Author(s):  
J.C.T. Rendell ◽  
D.S. Zimmerman ◽  
A.J. van der Est ◽  
E.E. Burnell
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Moment Tensor ◽  
Orientational Order ◽  
Mean Field ◽  
Field Potential ◽  
Intermolecular Forces ◽  
Sample Tube ◽  
Average Electric Field ◽  
Nematic Solvent

The order parameter matrices of a molecule that has no symmetry, 1,3-dichloro-2-ethenylbenzene, dissolved in two different nematic liquid-crystal solvents are analyzed in terms of various models for the intermolecular mean-field potential. In a mixture of liquid crystals for which the interaction between the molecular quadrupole moment tensor and the average electric field gradient of the nematic solvent has been minimized, the orientational order is best described by models for the short-range anisotropic potential. The most successful potentials are written in terms of anisotropic interactions between the solute surface and the liquid-crystal mean field. This represents a strong test of such models because they simultaneously fit the five independent orientational parameters obtained from the same solute, thus removing the problems associated with comparing results among different solutes in either the same or a different sample tube. Keywords: liquid crystals, intermolecular forces, order parameters, anisotropic.

The orientational behaviour of dichlorobenzenes in nematic liquid crystal solvents

1989 ◽  
Vol 67 (1) ◽  
pp. 54-59 ◽  
Author(s):  
C. T. Yim ◽  
D. F. R. Gilson
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Potential Energy ◽  
Electric Field ◽  
Electric Field Gradient ◽  
Short Range ◽  
Orientational Order ◽  
Energy Parameters ◽  
Average Electric Field ◽  
Shape And Size

The orientational order parameters of ortho-, meta-, and para-dichlorobenzene, dissolved in the nematic solvents EBBA and 1132, have been measured as functions of temperature and concentration, and used to determine the values of the potential energy parameters for each solute–solvent pair. These potentials have been interpreted in terms of a short-range contribution, which depends upon the shape and size of the solute molecule, plus a long-range term due to the interaction between the average electric field gradient from the solvent and the molecular quadrupole moment of the solute. Keywords: dichlorobenzenes, nematic solvents, liquid crystals, orientation, potential energy parameters.

Line broadening in the electron resonance spectra of spin probes dissolved in anisotropic media: the effect of nuclear spin quantization

1977 ◽  
Vol 353 (1672) ◽  
pp. 87-102 ◽  
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Nuclear Spin ◽  
Dynamic Properties ◽  
Orientational Order ◽  
Anisotropic Media ◽  
Approximate Theory ◽  
Spin Probes ◽  
Line Broadening ◽  
Electron Resonance

The line broadening in the electron resonance spectra of monoradicals dissolved in anisotropic media, such as liquid crystals, provides a valuable probe of both the orientational order and the molecular dynamics. However, the fast-motion relaxation theory employed to extract this information from the linewidths assumes that the nuclear spin is quantized along the direction of the magnetic field. This approximation is only correct when the symmetry axis of a uniaxial liquid crystal is either parallel or perpendicular to the field. We have therefore removed this assumption and have developed a general theory of line broadening valid for all orientations of the liquid crystal. The theory is then used to evaluate the angular dependence of the linewidths and this is compared with the dependence predicted by the approximate theory, for two classes of nitroxide spin probes. These comparisons reveal that for steroidal spin probes the error, introduced by assuming the nuclear spin to be quantized along the field, is confined to the dynamic properties derived from the linewidths. In contrast, significant errors appear in both the dynamic and static properties obtained from an analysis of the linewidth variations for fatty acid spin probes based on the approximate theory. It would seem that the exact theory must be employed to obtain precise information from linewidth investigations of liquid crystals, except when the orientational order is extremely small.

scholarly journals Liquid crystals of carbon nanotubes and graphene

2013 ◽  
Vol 371 (1988) ◽  
pp. 20120499 ◽  
Author(s):  
Cécile Zakri ◽  
Christophe Blanc ◽  
Eric Grelet ◽  
Camilo Zamora-Ledezma ◽  
Nicolas Puech ◽  
...  
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Order Parameter ◽  
Orientational Order ◽  
Point Of View ◽  
General Point ◽  
Conductivity Anisotropy ◽  
Conductive Films ◽  
Experimental Approaches ◽  
New Methodologies

Liquid crystal ordering is an opportunity to develop novel materials and applications with spontaneously aligned nanotubes or graphene particles. Nevertheless, achieving high orientational order parameter and large monodomains remains a challenge. In addition, our restricted knowledge of the structure of the currently available materials is a limitation for fundamental studies and future applications. This paper presents recent methodologies that have been developed to achieve large monodomains of nematic liquid crystals. These allow quantification and increase of their order parameters. Nematic ordering provides an efficient way to prepare conductive films that exhibit anisotropic properties. In particular, it is shown how the electrical conductivity anisotropy increases with the order parameter of the nematic liquid crystal. The order parameter can be tuned by controlling the length and entanglement of the nanotubes. In the second part of the paper, recent results on graphene liquid crystals are reported. The possibility to obtain water-based liquid crystals stabilized by surfactant molecules is demonstrated. Structural and thermodynamic characterizations provide indirect but statistical information on the dimensions of the graphene flakes. From a general point of view, this work presents experimental approaches to optimize the use of nanocarbons as liquid crystals and provides new methodologies for the still challenging characterization of such materials.

scholarly journals Doping liquid crystals with nanoparticles. A computer simulation of the effects of nanoparticle shape

2016 ◽  
Vol 18 (4) ◽  
pp. 2428-2441 ◽  
Author(s):  
Silvia Orlandi ◽  
Erika Benini ◽  
Isabella Miglioli ◽  
Dean R. Evans ◽  
Victor Reshetnyak ◽  
...  
Keyword(s):  
Computer Simulation ◽  
Monte Carlo ◽  
Liquid Crystal ◽  
Liquid Crystals ◽  
Monte Carlo Simulations ◽  
Orientational Order ◽  
Nanoparticle Shape ◽  
Nanoparticle Dispersions ◽  
Molecular Scale ◽  
Clearing Temperature

Molecular-scale Monte Carlo simulations of liquid crystal-nanoparticle dispersions show the effect on the orientational order and on the clearing temperature of shape and concentration of the dopant nanoparticles.

The orientational ordering of solute molecules in nematic solvents: cyanobenzenes, bromobenzenes, and p-benzoquinone in EBBA and 1132

1990 ◽  
Vol 68 (6) ◽  
pp. 875-880 ◽  
Author(s):  
C. T. Yim ◽  
D. F. R. Gllson
Keyword(s):  
Liquid Crystals ◽  
Potential Energy ◽  
Electric Field Gradient ◽  
Short Range ◽  
Orientational Order ◽  
Short Range Interaction ◽  
Range Interaction ◽  
Average Electric Field ◽  
Orientational Ordering ◽  
Shape And Size

The orientational order parameters of benzonitrile and o-, m-, and p-dicyanobenzene, monobromo- and p-dibromobenzene, and p-benzoquinone, dissolved in two nematic solvents, 1132 and EBBA, have been measured as functions of temperature, and used to determine the potential energy parameters for each solute–solvent pair. These parameters have been correlated with a short-range interaction based upon a shape and size function of the solute molecule and a long-range contribution due to the interaction between the solute molecular quadrupole moment and the average electric field gradient. Keywords: nematic liquid crystals, orientational ordering of solutes.

Static and Hydrodynamic Properties of Nematic Liquid Crystals

1992 ◽  
Vol 47 (4) ◽  
pp. 565-572 ◽  
Author(s):  
A. Chrzanowska ◽  
K. Sokalski
Keyword(s):  
Liquid Crystals ◽  
Nematic Liquid Crystals ◽  
Mean Field ◽  
Field Potential ◽  
Hydrodynamic Theory ◽  
Intermolecular Potential ◽  
Static Properties ◽  
Hydrodynamic Properties ◽  
Viscosity Coefficients ◽  
Rotational Viscosity

AbstractThe static properties of nematic liquid crystals are summarized. The mean field potential emerging from the static distribution function has been used to the hydrodynamic theory. Rotational viscosity coefficients have been investigated. The Parodi relation has been shown to be completely satisfied. Static and hydrodynamic properties have been predicted on the basis of one intermolecular potential

Phase Diagram and Orientational Order of a System with Second and Fourth Rank Interactions

1997 ◽  
Vol 11 (16) ◽  
pp. 1937-1944 ◽  
Author(s):  
Cesare Chiccoli ◽  
Paolo Pasini ◽  
Claudio Zannoni
Keyword(s):  
Phase Diagram ◽  
Monte Carlo ◽  
Liquid Crystals ◽  
Computer Simulations ◽  
Order Parameter ◽  
Orientational Order ◽  
Mean Field ◽  
Rank One ◽  
Site Cluster ◽  
Typical Temperature

A simple generalized Lebwohl–Lasher model for liquid crystals, where a fourth rank interaction is added to the usual second rank one, is investigated in detail. We have obtained the phase diagram of the system performing extensive Monte Carlo computer simulations for a range of the fourth to the second rank relative strengths and we compare it with the prediction of Mean Field and Two Site Cluster theories. We show that the addition of a non-negligible fourth rank term significantly changes the temperature dependence of the order parameter. Fourth rank contributions larger than 20% worsen the agreement of the model with the typical temperature behavior of the order in nematics.

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