Studies on Some Smectogenic Compounds with Large Bilayer Spacings

Madhusudana, N. V.; Srikanta, B. S.; Urs, M. Subramanya Raj

doi:10.1080/00268948308073140

Cited by 19 publications

(3 citation statements)

References 17 publications

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“…6 dans Ref. [43]). [Thermal evolution of the degree of head-to-head association of the molecules as calculated using a model of « chemical equilibrium » with two energy levels (see Ref [42] (Fig.…”

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confidence: 99%

Conjectures sur le comportement smectique A des mésogènes dissymétriques et fortement polaires

Guillon

Skoulios

1984

J. Phys. France

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Résumé. 2014 Abstract. 2014 In this qualitative paper, we recall the main features of the model that we recently proposed to describe the structural behaviour of the smectic A mesophases obtained with dissymmetric and highly polar smectogens. This model involves the mixture of single molecules and of pairs of head-to-head associated molecules. We also present the way to calculate the geometrical parameters characteristic of the smectic ordering, such as the degree of head-to-head association of the molecules, and the molecular area of the rigid cores and of the aliphatic chains. We next consider the effect of the three main factors that, in our opinion, play a prominent part in the smectic ordering : the amphiphilic character, the conformational disorder of the aliphatic chains, and the electrostatic interactions of the permanent dipoles located within the rigid cores or at their free end. Furthermore, we discuss the way these factors act upon the occurrence, the stability and the thermal evolution of the smectic A order. We then try to understand some of the typical behaviours of the partially bilayered, the single and double-layered smectic mesophases ; of the two-dimensional smectic A mesophase ; and of the reentrant phenomenon.

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confidence: 99%

Conjectures sur le comportement smectique A des mésogènes dissymétriques et fortement polaires

Guillon

Skoulios

1984

J. Phys. France

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“…These ndings are sup- [22]. Similar eOE ects on the dielectric properties of other liquid crystalline derivatives, having terminal or lateral ported by measurement of the anisotropy of polarizability (Da/A Ã 3 ) of the C Ar -X bonds of mono-substitute d benzenes; nitro substituents, have been demonstrate d in [116,237,305,306] and [106,215,307], respectively. this increases, depending on the substituent X, as follows [28]: F (0.5) < CH 3 (1.2) < Cl (2.5) < Br (3.9) < NO 2 It has been shown that mesogenic molecules possessing strongly polar terminal groups form associated pairs.…”

Section: Optical Propertiesmentioning

confidence: 89%

“…As can liquid crystals is a useful method for studying the eOE ects of the association of molecules on the structure of be seen from table 8, the replacement of one of the nitro Downloaded by [University of Nebraska, Lincoln] at 09:45 10 April 2015 Nitro substitution mesophases and consequently on the properties of liquid results in a decrease in average rate of thermal expansion of the layers and a change of sign of the curvature of crystals formed by these molecules [274][275][276][277][278]. The investigation of polar liquid crystals by XRD shows not the thermal dependence of the layer spacing in the smectic A phase [237]. The diOE erent d/L values probably only the existence of a layer structure in the smectic phase of these compounds, but also periodic density result from signi cantly diOE erent electron density distributions in the molecular structure (for pyridine uctuations in the nematic phase having a period d. The layers involve swarms containing tens to hundreds of derivatives this is shown in [289]) and steric factors which are responsible for the type of dimerization.…”

Section: -194] and Intermolecularmentioning

confidence: 99%

Nitro substitution in achiral calamitic liquid crystals

Petrov¹,

Shimizu

2001

Liquid Crystals

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Dielectric studies on binary mixtures containing 4‐trans‐4′ ‐n‐hexyl‐cyclohexyl‐isothiocyanato‐benzene

Raszewski

Dąbrowski

Stolarzowa

et al. 1987

Cryst. Res. Technol.

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We have studied binary mixtures with a n induced smectic phase of 4-trans-4'-n-hexylcycohexyl isothiocyanatobenzene (BCHBT) with 4-n-ethyl-4'-pentylazoxybenzene (EPAB) by means of dielectric, microscopic and refractometric measurements. The effective values of components p i and pi1 of the dipole moment per one molecule of the mixture have been calculated from values of E L and F J I . As a result of our studies, we have established that the heteroconiplexes formed in the mixture are so weak that they do not cause any esscntial changes in the distribution of niolecule charges. The observed deviations from additivity of the dielectric constant of the mixture are caused solely by a non-additive brhavior of the mixture density. Wir haben ein binares Gemisch aus 4 -t r a n s -4 ' -n -H e x y l c y c l o h e x y l i s o t h i o c y a r l 1 i (BCHBT) und 4-n-Ethyl-4'-pentylazaxybenzen (EPAB) mit sniektischer Induktionsphasc mittels dielektrischer, mikroskopischer und refraktrometrischer Messungrn untersucht.Mit Hilfe der dielektrischen Konstanten der nematischen Phase des Gemisches e l und F J I wurden die effektiven Werte der Dipolrnomentkomponenten p l und pll fur ein Molekiil des Gemisches berechnet. Auf Grund von Untersuchungen haben wir festgestellt : Die iin Gcmisch entstehenden Heterokornplexe sind so schwach, daS sie keine wesentlichen Vrranderungen der Ladungsverteilung der Molekiile verursachen. Die betrachteten Abweichungen von den atlditiven Werten der dielektrischen Konstanten des Gemisches werdcn nur durch nichtadditives Verhalten der Gemischdichte verursacht.

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Studies on Some Smectogenic Compounds with Large Bilayer Spacings

Cited by 19 publications

References 17 publications

Conjectures sur le comportement smectique A des mésogènes dissymétriques et fortement polaires

Conjectures sur le comportement smectique A des mésogènes dissymétriques et fortement polaires

Nitro substitution in achiral calamitic liquid crystals

Dielectric studies on binary mixtures containing 4‐trans‐4′ ‐n‐hexyl‐cyclohexyl‐isothiocyanato‐benzene

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