A generalized density-modulated twist-splay-bend phase of banana-shaped particles

AbstractIn 1976, Meyer predicted that bend distortions of the nematic director field are complemented by deformations of either twist or splay, yielding twist-bend and splay-bend nematic phases, respectively. Four decades later, the existence of the splay-bend nematic phase remains dubious, and the origin of these spontaneous distortions uncertain. Here, we conjecture that bend deformations of the nematic director can be complemented by simultaneous distortions of both twist and splay, yielding a twist-splay-bend nematic phase. Using theory and simulations, we show that the coupling between polar order and bend deformations drives the formation of modulated phases in systems of curved rods. We find that twist-bend phases transition to splay-bend phases via intermediate twist-splay-bend phases, and that splay distortions are always accompanied by periodic density modulations due to the coupling of the particle curvature with the non-uniform curvature of the splayed director field, implying that the twist-splay-bend and splay-bend phases of banana-shaped particles are actually smectic phases.

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Untersuchung der elektrischen Leitfähigkeit homologer N-(4-n-Alkyloxybenzyliden)-4'-n-butylaniline im nematischen und smektischen Phasenbereich / Investigation of the Electrical Conductivity of Homologous N-(4-n-alkoxybenzylidene)-4'-nbutylanilines in the Nematic and Smectic Phases

Zeitschrift für Naturforschung A ◽

10.1515/zna-1976-1238 ◽

1976 ◽

Vol 31 (12) ◽

pp. 1700-1706 ◽

Cited By ~ 2

Author(s):

G. Heppke ◽

F. Schneider ◽

A. Sterzl

Keyword(s):

Electrical Conductivity ◽

Chain Length ◽

Nematic Phase ◽

Alkyl Chain ◽

Electrolyte Concentration ◽

Alkyl Chain Length ◽

Anisotropy Ratio ◽

Concentration Effects ◽

Smectic Phases ◽

Nematic Phases

Abstract Investigation The electrical conductivity of the first eight homologous N-(4-n-alkoxybenzylidene)-4'-n-butylanilines is investigated in the isotropic, nematic and smectic phases using the electrolyte tetra-butylammonium picrate. The anisotropy ratio of the electrical conductivity shows pretransition behaviour in the nematic phases close to the transition to the smectic phases. This behaviour be-comes more distinct with increasing alkyl chain length of the liquid crystals. In the nematic phase of 40·4 an anisotropy ratio of V = 0.55 is determined at the lowest electrolyte concentration. Values of about V=0.05 were found in the smectic phases of several homologues. In the nematic phase, an increase of the electrolyte concentration effects an increase of the anisotropy ratio. This effect is systematically enhanced with increasing alkyl chain length.

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On the molecular origins of the ferroelectric splay nematic phase

Nature Communications ◽

10.1038/s41467-021-25231-0 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Richard J. Mandle ◽

Nerea Sebastián ◽

Josu Martinez-Perdiguero ◽

Alenka Mertelj

Keyword(s):

Nematic Phase ◽

Room Temperature ◽

Molecular Design ◽

Deep Understanding ◽

Formation Mechanisms ◽

Subtle Change ◽

Polar Order ◽

Long Time ◽

Nematic Phases ◽

Dynamics Simulations

AbstractNematic liquid crystals have been known for more than a century, but it was not until the 60s–70s that, with the development of room temperature nematics, they became widely used in applications. Polar nematic phases have been long-time predicted, but have only been experimentally realized recently. Synthesis of materials with nematic polar ordering at room temperature is certainly challenging and requires a deep understanding of its formation mechanisms, presently lacking. Here, we compare two materials of similar chemical structure and demonstrate that just a subtle change in the molecular structure enables denser packing of the molecules when they exhibit polar order, which shows that reduction of excluded volume is in the origin of the polar nematic phase. Additionally, we propose that molecular dynamics simulations are potent tools for molecular design in order to predict, identify and design materials showing the polar nematic phase and its precursor nematic phases.

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Megahertz Dielectric Relaxation in the Nematic Phases of 4,4′-di-n-propyloxyazoxybenzene and 4,4′-di-n-pentyloxyazoxybenzene

Zeitschrift für Naturforschung A ◽

10.1515/zna-1985-0614 ◽

1985 ◽

Vol 40 (6) ◽

pp. 627-631

Author(s):

Nguyen X. Phuc ◽

W. Otowski ◽

J. Chruściel ◽

H. Kresse ◽

S. Urban ◽

...

Keyword(s):

Dielectric Properties ◽

Dielectric Relaxation ◽

Homologous Series ◽

Nematic Phase ◽

Relaxation Times ◽

Relaxation Processes ◽

Frequency Range ◽

The Third ◽

Nematic Director ◽

Nematic Phases

The dielectric properties of the third (3. OAOB) and fifth (5. OAOB) members of the PAA homologous series have been investigated in the frequency range from 0.1 to 12 MHz. Negative dielectric anisotropies have been obtained in the nematic phase of both substances. For the dielectric relaxation processes observed parallel to the nematic director, the relaxation times and activation energies have been estimated and discussed.

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Optical manipulation of the nematic director field around microspheres covered with an azo-dendrimer monolayer

Optics Express ◽

10.1364/oe.22.020087 ◽

2014 ◽

Vol 22 (17) ◽

pp. 20087 ◽

Cited By ~ 15

Author(s):

Pemika Hirankittiwong ◽

Nattaporn Chattham ◽

Jumras Limtrakul ◽

Osamu Haba ◽

Koichiro Yonetake ◽

...

Keyword(s):

Optical Manipulation ◽

Director Field ◽

Nematic Director

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From Bend to Splay Dominated Elasticity in Nematics

Crystals ◽

10.3390/cryst11070831 ◽

2021 ◽

Vol 11 (7) ◽

pp. 831

Author(s):

Davide Revignas ◽

Alberta Ferrarini

Keyword(s):

Liquid Crystal ◽

Nematic Phase ◽

Low Cost ◽

Elastic Behavior ◽

Computational Investigation ◽

Apical Angle ◽

Polar Order ◽

The Past ◽

Bend Angles ◽

Analogous Effect

In the past decade, much evidence has been provided for an unusually low cost for bend deformations in the nematic phase of bent-core mesogens and bimesogens (liquid crystal dimers) having a bent shape on average. Recently, an analogous effect was observed for the splay mode of bent-core mesogens with an acute apical angle. Here, we present a systematic computational investigation of the Frank elastic constants of nematics made of V-shaped particles, with bend angles ranging from acute to obtuse. We show that by tuning this angle, the elastic behavior switches from bend dominated (K33>K11) to splay dominated (K11>K33), with anomalously low values of the splay and the bend constant, respectively. This is related to a change in the shape polarity of particles, which is associated with the emergence of polar order, longitudinal for splay and transversal for bend deformations. Crucial to this study is the use of a recently developed microscopic elastic theory, able to account for the interplay of mesogen morphology and director deformations.

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Synthesis of 4-Chloro-1,3-Diazobenzene Bent-Cores Liquid Crystals and Characterizations of Their Mesogenic Behaviors and Photoisomerization Phenomena

10.26434/chemrxiv.12115878.v1 ◽

2020 ◽

Author(s):

Jinying Lu ◽

Zelong Zhang ◽

Daoren Yan ◽

Zhiyong Zhang ◽

Jintao Guan ◽

...

Keyword(s):

Phase Transition ◽

Liquid Crystals ◽

Nematic Phase ◽

Dipole Moments ◽

Intermolecular Forces ◽

Acetate Solution ◽

Molecular Dipole ◽

Practical Applications ◽

Nematic Phases ◽

Terminal Chain

Azobenzene-based bent-core liquid crystals demonstrate a variety of mesomorphic behaviors and photochromic properties which are desirable for optical switching. Nowadays azobenzene-based bent-core liquid crystal (ABLC) compounds usually exhibit at least one of the following traits which are unfavorable for practical applications: (1) narrow temperature windows of nematic phases, (2) high phase transition temperature, and (3) long period of light stimulation to reach photostationary states. In this study, a series of ABLC compounds 4a–4g were synthesized by adding azo functional groups and chlorine substituent to the central bent-cores to form 4-chloro-1,3-dizaophenylene bent-cores. These ABLC compounds were characterized by i. fourier-transform infrared spectroscopy (FTIR), 1H and 13C nuclear magnetic resonance (NMR), and mass spectrometry (MS) for their structures, ii. differential scanning calorimetry (DSC) and polarized optical microscopy (POM) for their mesogenic properties, and iii. ultraviolet–visible spectroscopy (UV-Vis) and POM for their photosensitivity. The experimental results show that all compounds exhibited broad temperature windows of mesogenic phases. In particular, compound 4c showed a broad temperature window of 63.8 °C for nematic phase. Molecular simulations indicate that the molecular dipole moments of compounds 4a–4g are closely associated with the temperatures of Sm – N phase transition and temperature ranges of nematic phases. In addition, simulation results reveal that the terminal alkyl chains exhibit a diphasic effect on the molecular polarity: extending the terminal chain can initially reduce and then increase the molecular dipole moments due to the severe structural disorder of overly extended terminal chain. These findings indicate that the intermolecular forces play a vital role in shaping the mesogenic behavior of ABLCs. Comprehensive characterizations of photochromatic properties show that 4c was highly photosensitive and displayed rapid photoisomerization processes. At room temperature, compound 4c dissolved in ethyl acetate solution can reach photostationary state in 10 seconds. At 95 °C, compound 4c in nematic phase became isotropic liquid under UV-irradiation in 3 seconds due to the forward trans – cis photoisomerization and can be restored to be nematic under natural visible light in 5 seconds because of the backward cis – trans photoisomerization. This study linking the mechanistic details with mesogenic properties provides valuable insights to improve future design of azobenzene bent-core liquid crystals for practical applications especially in photonic applications. Pertinent molecular structure files (mol2) can be downloaded from<a href="https://github.com/er1czz/ABLC">https://github.com/er1czz/ABLC</a>

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Role of molecular bend angle and biaxiality in the stabilization of the twist-bend nematic phase

Soft Matter ◽

10.1039/d0sm00078g ◽

2020 ◽

Vol 16 (18) ◽

pp. 4350-4357 ◽

Cited By ~ 2

Author(s):

Wojciech Tomczyk ◽

Lech Longa

Keyword(s):

Field Theory ◽

Nematic Phase ◽

Mean Field Theory ◽

Mean Field ◽

Structural Features ◽

Bend Angle ◽

Nematic Phases

Within mean-field theory for V-shaped molecules, we have investigated how the alteration of a molecule's structural features influence the stabilization of modulated and non-modulated nematic phases.

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Peculiarities in the Director Reorientation and the NMR Spectra Evolution in a Nematic Liquid Crystals under the Effect of Crossed Electric and Magnetic Fields

Crystals ◽

10.3390/cryst9050262 ◽

2019 ◽

Vol 9 (5) ◽

pp. 262 ◽

Cited By ~ 1

Author(s):

Alex V. Zakharov ◽

Izabela Sliwa

Keyword(s):

Nematic Phase ◽

Viscosity Coefficient ◽

Threshold Value ◽

Periodic Patterns ◽

Director Field ◽

Electric And Magnetic Fields ◽

Spatially Periodic ◽

Rotational Viscosity ◽

Director Reorientation ◽

Reorientational Dynamics

The illustrative description of the field-induced peculiarities of the director reorientation in the microsized nematic volumes under the effect of crossed magnetic B and electric E fields have been proposed. The most interesting feature of such configuration is that the nematic phase becomes unstable after applying the strong E . The theoretical analysis of the reorientational dynamics of the director field provides an evidence for the appearance of the spatially periodic patterns in response to applied large E directed at an angle α to B . The feature of this approach is that the periodic distortions arise spontaneously from a homogeneously aligned nematic sample that ultimately induces a faster response than in the uniform mode. The nonuniform rotational modes involve additional internal elastic distortions of the conservative nematic system and, as a result, these deformations decrease of the viscous contribution U vis to the total energy U of the nematic phase. In turn, that decreasing of U vis leads to decrease of the effective rotational viscosity coefficient γ eff ( α ) . That is, a lower value of γ eff ( α ) , which is less than one in the bulk nematic phase, gives the less relaxation time τ on ( α ) ∼ γ eff ( α ) , when α is bigger than the threshold value α th . The results obtained by Deuterium NMR spectroscopy confirm theoretically obtained dependencies of τ on ( α ) on α .

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Study of the Liquid Crystalline Phases in Some Compounds of 4-Trans-(4-Alkyl)Cyclo-Hexylphenyl-Alkylcarboxylate

Zeitschrift für Naturforschung A ◽

10.1515/zna-1983-1213 ◽

1983 ◽

Vol 38 (12) ◽

pp. 1362-1364 ◽

Cited By ~ 1

Author(s):

I. H. Ibrahim ◽

W. Haase

Keyword(s):

Differential Scanning Calorimetry ◽

Nematic Phase ◽

Liquid Crystalline ◽

Intermolecular Distance ◽

X Ray Diffraction ◽

Scanning Calorimetry ◽

X Ray ◽

Enthalpy Changes ◽

Liquid Crystalline Phases ◽

Nematic Phases

Abstract Three mesogenic compounds of the general formula have been investigated by differential scanning calorimetry. thermal optical microscopy and X-ray diffraction methods/Enthalpy changes of The different phase transitions for these compounds have been determined. H33 exhibits smectic B and nematic phases, whereas H34 and H75 exhibit only smectic B phases. The thickness of the smectic layers and the average intermolecular distance have been evaluated, as well as the corresponding molecular parameters in the nematic phase.

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Flow-induced order–order transitions in amyloid fibril liquid crystalline tactoids

Nature Communications ◽

10.1038/s41467-020-19213-x ◽

2020 ◽

Vol 11 (1) ◽

Cited By ~ 1

Author(s):

Hamed Almohammadi ◽

Massimo Bagnani ◽

Raffaele Mezzenga

Keyword(s):

Liquid Crystalline ◽

Extensional Flow ◽

Energy Functional ◽

Field Configuration ◽

Quasi Equilibrium ◽

Functional Theory ◽

Director Field ◽

Anisotropic Surface ◽

Inverse Power Law ◽

Nematic Phases

Abstract Liquid crystalline droplets, also known as tactoids, forming by nucleation and growth within the phase diagram region where isotropic and nematic phases coexist, challenge our understanding of liquid crystals under confinement due to anisotropic surface boundaries at vanishingly small interfacial tension, resulting in complex, non-spherical shapes. Little is known about their dynamical properties, since they are mostly studied under quiescent, quasi-equilibrium conditions. Here we show that different classes of amyloid based nematic and cholesteric tactoids undergo order–order transitions by flow-induced deformations of their shape. Tactoids align under extensional flow, undergoing extreme deformation into highly elongated prolate shapes, with the cholesteric pitch decreasing as an inverse power-law of the tactoids aspect ratio. Free energy functional theory and experimental measurements are combined to rationalize the critical elongation above which the director-field configuration of tactoids transforms from bipolar and uniaxial cholesteric to homogenous and to debate on the thermodynamic nature of these transitions.

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