Columnar, Discotic Nematic and Lamellar Liquid Crystals: Their Structures and Physical Properties

Chandrasekhar, S.; Demus, D.; Goodby, John W.; Gray, G. W.; Spiess, H. W.; Vill, V.

doi:10.1002/9783527620623.ch5

Cited by 40 publications

(13 citation statements)

References 105 publications

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“…In general, 2-D lattices are unstable [ 40 ] but in this case they are stabilized by the curvature elasticity (bending) of the columns [ 41 ] (p. 398). X-ray diffraction, both on monodomains and on powder samples, has been the most common experimental technique used to assess the nature of molecular order within such phases [ 42 ], although most investigations take advantage of contributions deriving from differential scanning calorimetry (DSC) and polarized optical microscopy (POM), while the role played by nuclear magnetic resonance (NMR) spectroscopy is also relevant [ 43 , 44 , 45 ]. Figure 3 contains illustrations of different columnar organizations, as observed within a cross-section normal to the direction of the columns.…”

Section: Discotic Mesophasesmentioning

confidence: 99%

Charge Mobility in Discotic Liquid Crystals

Termine

Golemme

2021

IJMS

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Discotic (disk-shaped) molecules or molecular aggregates may form, within a certain temperature range, partially ordered phases, known as discotic liquid crystals, which have been extensively studied in the recent past. On the one hand, this interest was prompted by the fact that they represent models for testing energy and charge transport theories in organic materials. However, their long-range self-assembling properties, potential low cost, ease of processability with a variety of solvents and the relative ease of tailoring their properties via chemical synthesis, drove the attention of researchers also towards the exploitation of their semiconducting properties in organic electronic devices. This review covers recent research on the charge transport properties of discotic mesophases, starting with an introduction to their phase structure, followed by an overview of the models used to describe charge mobility in organic substances in general and in these systems in particular, and by the description of the techniques most commonly used to measure their charge mobility. The reader already familiar or not interested in such details can easily skip these sections and refer to the core section of this work, focusing on the most recent and significant results regarding charge mobility in discotic liquid crystals.

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Section: Discotic Mesophasesmentioning

confidence: 99%

Charge Mobility in Discotic Liquid Crystals

Termine

Golemme

2021

IJMS

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“…liquid crystals whose constituent molecules are disc-like rather than rod-like) for which α 3 > 0. 38 Specifically, the analysis for non-flow-aligning calamitics (with α 2 < 0 and α 3 > 0) also applies to non-flow-aligning discotics, and the analysis for flow-aligning calamitics (with α 2 < 0 and α 3 < 0) follows through to the case of flow-aligning discotics (with α 2 > 0 and α 3 > 0) with only minor differences.…”

Section: Discussionmentioning

confidence: 99%

Shear-driven and pressure-driven flow of a nematic liquid crystal in a slowly varying channel

et al. 2006

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Motivated by the industrially important processes of blade coating and cavity filling of liquid crystalline materials, we consider steady, two-dimensional shear-driven (Couette) and pressure-driven (plane Poiseuille) flow of a thin film of a nematic liquid crystal in the slowly varying channel formed between a fixed blade of prescribed shape and a planar substrate. Specifically, blade coating motivates the study of shear-driven flow due to the motion of the substrate parallel to itself with constant velocity, while cavity filling motivates the study of pressure-driven flow due to an imposed pressure drop. We use a combination of analytical and numerical techniques to analyse the Ericksen--Leslie equations governing the fluid velocity and pressure and the director orientation in cases when both the aspect ratio of the channel and the distortion of the director field are small. We demonstrate a variety of flow and director-orientation patterns occurring in different parameter regimes. In the limit of weak flow effects flow alignment does not occur and the appropriate solution of the governing equations is found explicitly. In the limit of strong flow effects flow alignment occurs and orientational boundary layers exist near the substrate and near the blade, and in addition, an orientational internal layer may also exist within which the director orientation changes from +theta_0 to -theta_0 where theta_0 is the flow-alignment angle

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“…IR (Nujol, NaCl): 3 130 (OH) and 1 597 cm -1 (C2O). 1 6 b was obtained by dissolving the b-diketone in a warm mixture of absolute ethanol (10 mL) and methanol (20 mL). After cooling the solution, palladium acetate (0.5 mmol) dissolved in cold ethanol was added and the resulting mixture was stirred for 8 h. The precipitate was filtered off and washed with methanol.…”

Section: Experimental Partmentioning

confidence: 99%

“…However, polymers based on discotic mesogenic units have been relatively less explored despite the variety of low molecular weight compounds described as discotic mesogens. [1] Organic LCPs having disk-shaped mesogens either as an integral part of the polymeric main chain [2][3][4] or attached as side groups [5,6] on a polymeric backbone have been investigated in recent years as well as discotic polymeric networks [7] or elastomers. [8] Metal coordination chemistry has brought about a considerable expansion in the field of discotic liquid crystals since coordination chemistry offers new possibilities for the design of discotic mesogens.…”

Section: Introductionmentioning

confidence: 99%

Liquid crystalline polymers containing discotic metallomesogens in the main chain

Valdebenito

Oriol²,

Barberá

et al. 2000

Macromol. Chem. Phys.

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Metallomesogenic polymers having discotic units in the main chain have been synthesized using β‐diketonates of Cu(II) and Pd(II) as monomers. The corresponding homologues of low molecular weight have also been synthesized as models of the polymers. All the materials prepared exhibit columnar mesophases. The model compounds exhibit a columnar hexagonal mesophase. In the case of the polymers, the more flexible polymers 2 a and 2 b show a columnar hexagonal mesophase whereas the more rigid polymers 1 a and 1 b exhibit a columnar rectangular mesophase. Fibers of these polymers have an orientation of the polymeric chains along the stretching direction and the disk‐like units are arranged in columns perpendicular to the fiber axis.

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Columnar, Discotic Nematic and Lamellar Liquid Crystals: Their Structures and Physical Properties

Cited by 40 publications

References 105 publications

Charge Mobility in Discotic Liquid Crystals

Charge Mobility in Discotic Liquid Crystals

Shear-driven and pressure-driven flow of a nematic liquid crystal in a slowly varying channel

Liquid crystalline polymers containing discotic metallomesogens in the main chain

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