A molecular field theory of smectic A liquid crystals

Kventsel, G. F.; Luckhurst, G. R.; Zewdie, Habtamu

doi:10.1080/00268978500102541

Cited by 48 publications

(27 citation statements)

References 20 publications

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“…In the original McMillan theory, the order parameter for the smectic A phase is given by 2 cosq cos 2p . It has been reported that the decoupled approximation: cosq cos 2p 2 cos q cos 2p 2 is in qualitative agreement with the original McMillan theory [77]. A-nematic phase transition (SNT) is of second order, while the NIT is of first order.…”

Section: Smectic-nematic-isotropic Phase Separationssupporting

confidence: 64%

Thermodynamics of Flexible and Rigid Rod Polymer Blends

Matsuyama

2010

Encyclopedia of Polymer Blends

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Binary mixtures of a flexible polymer and a low molecular weight liquid crystalline molecule, or a rigid rod-like molecule, are of interest because of their important technological applications in high modulus fibers, nonlinear optics, and electro optical devices. These blends are basic materials for recent new technologies of liquid crystal displays [1,2]. The performances of these systems are closely related to phase separations and conformations of polymer chains dissolved in a liquid crystalline phase. One of the main problems is to examine the location of various phases such as isotropic, nematic, and smectic phases, depending on temperature and concentra tion. To understand the thermodynamics and thermal instability of these blends, it is important to consider the co-occurrences between liquid crystalline ordering and phase separations.Generally, polymer chains exhibit a variety of flexibility, from flexible to rigid rodlike polymers. Polymer blends containing a liquid crystalline ordering have received considerable attention. The volume of literature on the theories and experiments of liquid crystallinity in polymer blends is now very extensive. There are many theoretical models for liquid crystalline polymers, such as the Flory lattice model [3][4][5][6][7][8], wormlike chain model [9][10][11], and Onsager virial theory [12] for rigid rods. An example of a recent review of liquid crystalline polymers is the text book of Donald and Windle [13].In this chapter we introduce the thermodynamics, or phase behavior, of binary mixtures of a flexible polymer and a rigid rod-like molecule. Here the flexible polymer means that liquid crystalline ordering does not occur in the constituent pure polymer. We first describe the fundamentals of a nematic phase, based on the Onsager theory for a rigid rod, where the entropy-induced nematic ordering is discussed. This will be the basis of the following sections. In Section 2.3, we focus on the phase separations of mixtures of a flexible polymer and a rigid rod-like molecule, or a low molecular weight liquid crystalline molecule, in a thermal equilibrium state. We introduce recent theoretical models to describe phase behavior, combining the Flory-Huggins Edited by Avraam I. Isayev

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Section: Smectic-nematic-isotropic Phase Separationssupporting

confidence: 64%

Thermodynamics of Flexible and Rigid Rod Polymer Blends

Matsuyama

2010

Encyclopedia of Polymer Blends

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“…Similar tendencies were deduced later from more complicated theoretical treatments including both attractive and repulsive potentials [23,24], but a merit of the attractive potential theory still lies in its simplicity. Especially, the recent recalculation by Kventsel et al [25] by applying the decoupling approximation r~ = qr instead of equation (7), made the comparison with the experimental data easier. In this section, therefore, our experimental data are analysed according to this theory.…”

Section: Discussionmentioning

confidence: 98%

Effect of terminal polar substituents on the nature of smectic A liquid crystals of a series of 4-(4″-octyloxybenzoyloxy)benzylidene-4′-substituted anilines

et al. 1990

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“…This decoupling approximation has the additional advantage that the strength of the correlation between orientational and translation coordinates is readily controlled. The results of this decoupled model have been compared quantitatively with the results of McMillan's theory by Kventsel et al [13] and found that the decoupled model for the S,-N transition is in qualitative and quantitative agreement with McMillan's theory and hence with experiment.…”

Section: Resultsmentioning

confidence: 60%

“…So, the DSC and density results show that the SA-N transition in both compounds is a weak first-order one, while the ESR measurements show a continuous change of orientational order parameter at the transition in DBBMA. To see whether these results are consistent or not, we compare them with the theoretical predictions; first with McMillan's theory of smectic A liquid crystals and second with the decoupled model of the smectic A phase proposed by Kventsel et al [13].…”

Section: Resultsmentioning

confidence: 66%

“…The predicted values of Ay (0.03 in DBBMA and 0.074 in DDBBMA) suggest a very small change in the orientational order parameter of the spin probe at the SA-N transition which is in reasonable agreement with the experimental observation of a smooth change in y for the probe in DBBMA and a very small jump (=0.05) in y for the probe in DDBBMA. The ratio of the strength parameter (m and y ) y/a values are found to be almost the same for both compounds (y/a = 0.70 in DBBMA and 0.72 in DDBBMA), which is expected to be constant in a homologous series [13]. The value of GAN/TNI calculated for the tricritical point in this homologous series using the y/m values is about 0.915 and very close to the T&TNI value of DBBMA.…”

Section: Resultsmentioning

confidence: 79%

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An Investigation of Smectic A—Nematic and Nematic—Isotropic Phase Transitions

Alapati

Saran

1991

Physica Status Solidi (b)

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The phases and phase transitions in two homologues of the 4-(4-n-alkyloxy-benzoyloxy) benzylidene-2-methylaniline (decyloxy and dodecyloxy) are characterized using a variety of experimental techniques. These are differential scanning calorimetry, thermal microscopy, X-ray diffraction, ESR spectroscopy, and density determination. The nematic-isotropic transition is found to be of first order but with a smaller transition entropy, in both of the compounds, than expected. The smectic A-nematic transition is found to be of weak first order in both of the compounds. The experimental results are compared to those of other compounds which have comparable molecular lengths and with the predictions of a molecular field theory of smectic A liquid crystals. Mit einer Vielzahl experimenteller Methoden werden die Phasen und Phaseniibergange in zweiHomologua des 4-(4'-n-alkyloxy-benzoyloxy) benzyliden-2"-methylanilin (

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A molecular field theory of smectic A liquid crystals

Cited by 48 publications

References 20 publications

Thermodynamics of Flexible and Rigid Rod Polymer Blends

Thermodynamics of Flexible and Rigid Rod Polymer Blends

Effect of terminal polar substituents on the nature of smectic A liquid crystals of a series of 4-(4″-octyloxybenzoyloxy)benzylidene-4′-substituted anilines

An Investigation of Smectic A—Nematic and Nematic—Isotropic Phase Transitions

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