Dielectric Relaxation Studies on Two Systems Exhibiting the Induced Smectic A Phase

Srikanta, B. S.; Madhusudana, N. V.

doi:10.1080/00268948408072096

Cited by 17 publications

(5 citation statements)

References 13 publications

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“…These values are comparatively higher than many calamatics in their respective phases. 41,42 Similar behaviour was also reported very recently in a binary liquid crystal mixture (rod and bent-core) showing N-SmC a phase transition. 40 Since the activation energy represents the energy barrier associated with the flip-over of the long molecular axis it suggests that the flip-over motion is relatively less easy in hockey stick or bent-core systems than in calamitic liquid crystals.…”

Section: Dielectric Relaxationsupporting

confidence: 86%

Structure–property correlation of a hockey stick-shaped compound exhibiting N-SmA-SmCa phase transitions

et al. 2012

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Section: Dielectric Relaxationsupporting

confidence: 86%

Structure–property correlation of a hockey stick-shaped compound exhibiting N-SmA-SmCa phase transitions

et al. 2012

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“…It seems justified to conclude that the thermal expansivity shows a small anisotropy which is more pronounced for the SmA d phase due to the competing effects mentioned already. This supports the suggestion given by Madhusudana et al [21,22] for explaining the decrease of the activation barrier hindering the molecular rotations around the short axes in the SmA phase in relation to the N phase. These authors claimed that this is due to anisotropic packing effects: the volume expansion causes an expansion mainly within the smectic layer, whereas the layer spacing hardly varies with temperature.…”

supporting

confidence: 90%

X‐ray studies of the layer thickness in smectic phases

2005

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X-ray investigations of nine smectogenic substances exhibiting the smectic A d , A 1 and crystalline E phases were performed at various temperatures. X-ray patterns yielded the layer thickness d (A d , A 1 phases) and orthorhombic unit cell parameters (E phase). The layer thickness of the A d phase in 49-n-alkyl-4-cyanobiphenyls (nCBs) has different temperature coefficients for shorter (n58 -10) and longer (n512 -14) members, which is explained as resulting from two competing effects: a weakening with temperature of the intermolecular association energy that favours an increase in d, and the increasing number of conformers which reduces the molecular length. A small anisotropy of the thermal expansivity in the smectic phases was found by comparing the linear quantity d(T) with the linearized bulk characteristic of the system, V 23 (T), where V51/r is the specific volume, r is the density. Differences between the slopes of the two quantities are less in the case of the A 1 phase of two nDBTs (5-n-alkyl-2-(49-isothiocyanatophenyl)-1,3-dioxanes). The present X-ray data and recent results of studies of the low frequency relaxation process in these compounds (under atmospheric as well as elevated pressures) give a consistent picture of molecular reorientations around the short axes in the smectic phases.

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“…No biphasic regions were detected at high MCB concentrations. Application of pressure (see figures [5][6][7][8][9] shows that a reentrant nematic phase is stabilized by pressure and at about 1010 bar the SA-N, phase boundary meets the N-SA line. The temperature of this invariant point, which we call the crossing point, is 54°C and the concentration xMCB is 0.90.…”

Section: Resultsmentioning

confidence: 95%

“…A hint that both types of phase diagram can be transformed into one another is given by the phase diagram for 4-n-butyloxyphenyl-4'-n-pentyloxybenzoate and 80CB [6]. This phase diagram shows besides the maximum of the induced S, phase a minimum in the phase boundary line N-S, on the 80CB side.…”

Section: Introductionmentioning

confidence: 98%

High pressure study on induced S_Aphases in binary liquid crystal mixtures

Illian¹,

Kneppe²,

Schneider³

1989

Liquid Crystals

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Binary mixtures of terminal polar and non-polar liquid crystals exhibiting induced smectic phases are studied under high pressure. For terminal polar compounds with smectic phases, there are two types of T, x phase diagrams known up to now. Diagrams with a nematic gap between the induced phase and the smectic phase of the terminal polar compound and diagrams with an uninterrupted miscibility of the smectic phases. We find a continuous transformation between these phase diagrams with pressure. At a certain pressure, the phase transition lines form a cross separating two nematic and two smectic phases. IntroductionMixtures of terminal polar and non-polar liquid crystals usually show phase diagrams with a very stable smectic phase (induced smectic phase) of the orthogonal type in the range of medium concentrations El, 21. If the pure terminal polar component also exhibits a smectic phase, two different types of phase diagram can be observed which are shown schematically in figures 1 and 2. An uninterrupted miscibility of the induced S, phase and the SA phase of the polar component (see figure I ) is usually found in mixtures of 4-n-octyloxy-4'-cyanobiphenyl(80CB) with terminal non-polar esters having long alkyl chains. Esters with short alkyl chains usually exhibit phase diagrams with a nematic gap [3] between the two smectic phases (see figure 2). On both sides of the nematic gap, the reentrant phenomenon, i.e. the phase sequence Nr,-SA-N, is observed. The question arises as to whether these two types of phase diagram are principally different. Such a principal difference could be caused by slight differences in the layer structure which is, in fact, different: a monolayer (S,,) for the induced phase [3, 41 and a bilayer (SAd) structure for the pure polar component [5].A hint that both types of phase diagram can be transformed into one another is given by the phase diagram for 4-n-butyloxyphenyl-4'-n-pentyloxybenzoate and 80CB [6]. This phase diagram shows besides the maximum of the induced S, phase a minimum in the phase boundary line N-S, on the 80CB side.It is known that the application of pressure reduces the stability of the S,, phase [7], whereas nearly all other liquid crystal phases are stabilized. Therefore, it is possible to change significantly the form of a phase diagram with an induced smectic phase by application of pressure. We have now tried to find the missing link between the different types of phase diagram with induced smectic phases by studying suitable binary systems under high pressure.

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Dielectric Relaxation Studies on Two Systems Exhibiting the Induced Smectic A Phase

Cited by 17 publications

References 13 publications

Structure–property correlation of a hockey stick-shaped compound exhibiting N-SmA-SmCa phase transitions

Structure–property correlation of a hockey stick-shaped compound exhibiting N-SmA-SmCa phase transitions

X‐ray studies of the layer thickness in smectic phases

High pressure study on induced S_Aphases in binary liquid crystal mixtures

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Dielectric Relaxation Studies on Two Systems Exhibiting the Induced Smectic A Phase

Cited by 17 publications

References 13 publications

Structure–property correlation of a hockey stick-shaped compound exhibiting N-SmA-SmCa phase transitions

Structure–property correlation of a hockey stick-shaped compound exhibiting N-SmA-SmCa phase transitions

X‐ray studies of the layer thickness in smectic phases

High pressure study on induced SAphases in binary liquid crystal mixtures

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High pressure study on induced S_Aphases in binary liquid crystal mixtures