scholarly journals A Bidimensional Gay-Berne Calamitic Fluid: Structure and Phase Behavior in Bulk and Strongly Confined Systems

2021 ◽  
Vol 8 ◽  
Author(s):  
A. Calderón-Alcaraz ◽  
J. Munguía-Valadez ◽  
S. I. Hernández ◽  
A. Ramírez-Hernández ◽  
E. J. Sambriski ◽  
...  
Keyword(s):  
Order Parameter ◽  
Nematic Phase ◽  
Orientational Order ◽  
Topological Defects ◽  
Md Simulations ◽  
Structural Behavior ◽  
Nematic Order ◽  
Lower Temperature ◽  
Geometry Characteristic ◽  
Strong Confinement

A bidimensional (2D) thermotropic liquid crystal (LC) is investigated with Molecular Dynamics (MD) simulations. The Gay-Berne mesogen with parameterization GB(3, 5, 2, 1) is used to model a calamitic system. Spatial orientation of the LC samples is probed with the nematic order parameter: a sharp isotropic-smectic (I-Sm) transition is observed at lower pressures. At higher pressures, the I-Sm transition involves an intermediate nematic phase. Topology of the orthobaric phase diagram for the 2D case differs from the 3D case in two important respects: 1) the nematic region appears at lower temperatures and slightly lower densities, and 2) the critical point occurs at lower temperature and slightly higher density. The 2D calamitic model is used to probe the structural behavior of LC samples under strong confinement when either planar or homeotropic anchoring prevails. Samples subjected to circular, square, and triangular boundaries are gradually cooled to study how orientational order emerges. Depending on anchoring mode and confining geometry, characteristic topological defects emerge. Textures in these systems are similar to those observed in experiments and simulations of lyotropic LCs.

scholarly journals Study of Molecular Polarizabilities and Orientational Order Parameter in the Nematic Phase of 6.O12O.6 and 7.O12O.7

2011 ◽  
Vol 01 (04) ◽  
pp. 167-174 ◽  
Author(s):  
Parameswara Rao Alapati ◽  
D. Bhuyan ◽  
D. Madhavi Latha ◽  
P. Pardhasaradhi ◽  
V. G. K. M. Pisipati ◽  
...  
Keyword(s):  
Order Parameter ◽  
Nematic Phase ◽  
Orientational Order ◽  
Orientational Order Parameter ◽  
Molecular Polarizabilities

Studies on binary mixtures of 4-pentyloxy-4′-cyanobiphenyl with three 4, 4′-di(alkoxy)azoxybenzenes

2010 ◽  
Vol 18 (2) ◽  
Author(s):  
B. Jaishi ◽  
P. Mandal ◽  
R. Dąbrowski
Keyword(s):  
Binary Mixtures ◽  
Order Parameter ◽  
Nematic Phase ◽  
Transition Point ◽  
Orientational Order ◽  
Smectic Phase ◽  
Refractive Indices ◽  
Orientational Order Parameter ◽  
Polarizability Anisotropy ◽  
Good Agreement

AbstractEighteen binary mixtures of 4-pentyloxy-4′-cyanobiphenyl (5OCB) and 4, 4′-di(alkoxy)azoxybenzenes (nOAB) with n = 5, 6, and 7 at different concentrations have been studied in detail. Over a wide concentration range, induced SmA phase was observed in all the mixtures except in one. In most of the mixtures, the refractive indices no, ne, and Δn lie between the values of pure components. The optical birefringence of the mixtures is found to decrease non-additively with concentration. The molecular polarizability anisotropy and the orientational order parameter <P2> of the mixtures were calculated. Nature of variation of polarizability anisotropy with concentration is similar to that of Δn. In allmixtures <P2> is more in smectic phase than in nematic phase and it also shows non-additive behaviour. Observed <P2> values of the mixtures were compared with McMillan’s and Maier-Saupe theoretical values and good agreement is found in some mixtures. The transition temperatures obtained by fitting <P2> data to McMillan’s theory agree with the observed values within a few degrees. Ratio of elastic constants K33 and K11 is determined for mixtures having nematic phase and found to diverge at TNA transition point.

An Optical Study on Orientational Order Parameter and Molecular Polarizability in Benzylidene Anilines

2011 ◽  
Vol 181-182 ◽  
pp. 102-105 ◽  
Author(s):  
M. Ramakrishna Nanachara Rao ◽  
P.V. Datta Prasad ◽  
V.G.K.M. Pisipati ◽  
D. Madhavi Latha
Keyword(s):  
Order Parameter ◽  
Nematic Phase ◽  
Field Model ◽  
Orientational Order ◽  
Internal Field ◽  
Molecular Polarizability ◽  
Refractive Indices ◽  
Polarizability Anisotropy ◽  
Optical Study ◽  
Molecular Polarizabilities

Refractive indices measurements are carried out in four alkoxy benzylidene anilines viz., N-(p-n-methoxy and ethoxy benzaldehyde)-p-n-dodecyl and tetra decyl anilines, 1O.12, 1O.14, 2O.12 and 2O.14. First three compounds exhibit monovariant nematic phase while the last compound exhibits nematic and SmA phases with variable thermal ranges. The molecular polarizabilities are calculated from the refractive indices and the density using the well known internal field models by Vuks and Neugebauer. The molecular polarizability anisotropy is estimated from the Lippincott δ-function model as well as molecular vibrational methods. The order parameter is estimated using a) from the Haller’s extrapolation from molecular polarizabilities, b) from the scaling factors obtained from the equations by Vuks and Neugbeaur and c) directly from the birefringence - a method developed by Kuczynski et al without considering any internal field model to the liquid crystal molecule. The results evaluated from these methods are compared from one another and the limitations of the methods used are discussed.

A continuum theory of disorder in nematic liquid crystals. I

1977 ◽  
Vol 353 (1673) ◽  
pp. 247-259 ◽  
Keyword(s):  
Ground State ◽  
Order Parameter ◽  
Nematic Phase ◽  
Mean Field Theory ◽  
Orientational Order ◽  
Mean Field ◽  
Continuum Theory ◽  
Wave Theory ◽  
Debye Theory ◽  
The Continuum

An alternative to the Maier-Saupe mean field theory of orientational order in nematics is suggested. It is a theory of disorder rather than order, analogous to the spin-wave theory of ferromagnetism. That is to say, the nematic is treated as a continuum with a perfectly aligned ground state, in which a spectrum of distortion modes involving splay, twist and bend are thermally excited with amplitudes determined by the Frank stiffness constants K 1 , K 2 and K 3 . It is argued that there cannot be more than 2 N independent modes, where N is the number of molecules, and a cut-off is applied to the spectrum accordingly, resembling the cut-off used in the Debye theory of solids. The theory is used to predict values for the con­ventional order parameter S 2 (= < P 2 (cos θ )>) and for higher order para­meters such as S 4 (= <P4(cos θ )>) in terms of K 1 , K 2 and K 3 , and the results agree adequately with experiment. Like the Maier-Saupe theory, the continuum theory suggests a minimum value for S 2 below which the nematic phase cannot be stable or even meta-stable. Refinements that might help to improve the agreement are discussed.

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