Characterization of the Submicrometer Hierarchy Levels in the Twist-Bend Nematic Phase with Nanometric Helices via Photopolymerization. Explanation for the Sign Reversal in the Polar Response

Панов, В. П.; Sreenilayam, Sithara P.; Panarin, Yu. P.; Vij, J. K.; Welch, Chris; Mehl, Georg H.

doi:10.1021/acs.nanolett.7b03441

Cited by 26 publications

(25 citation statements)

References 32 publications

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“…Even though, in principle, such an approach could be used to extend the temperature range over which the N TB phase is stable, it has not been reported so far. Photopolymerization of the N TB phase was performed by Panov et al [30] to demonstrate its usefulness in exploring complex hierarchical structures of the N TB phase.…”

Section: Introductionmentioning

confidence: 99%

Metastable room-temperature twist-bend nematic phases via photopolymerization

2019

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Section: Introductionmentioning

confidence: 99%

Metastable room-temperature twist-bend nematic phases via photopolymerization

2019

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“…[9][10][11] The TB phase is an example of a modulated nematic-like phase in which the average orientational order is also augmented with an additional periodic structure while still lacking positional order. The TB phase exhibits a electrooptic response on a timescale of a few microseconds, [12] and also provides a simple route to materials with defined nanostructures via in-situ photopolymerisation [13] which may find use in photonics. [14][15][16][17] Other modulated nematic-like phases are known to exist: Mertelj et al recently discovered a nematic-like mesophase with a periodic splay modulated structure (N S ), [18] and we recently reported a novel nematic-like phase in binary mixtures of bentdimers and a high helical twisting power additive.…”

Section: Introductionmentioning

confidence: 99%

Pentaerythritol Derived Tetrapode Exhibiting a Nematic‐Like Mesophase at Ambient Temperatures

Hann

Mandle

2019

ChemPhysChem

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The nematic liquid‐crystalline phase exhibits average orientational order, with no positional organisation. So‐called modulated nematic phases exhibit this same orientational order with an additional spatially periodic modulation of the nematic director, the most common of which is the twist‐bend nematic phase. We report a pentaerythritol derived tetrapode which exhibits a nematic‐like mesophase at ambient temperature, and we denote this new mesophase ‘NX’ to indicate a nematic phase of unknown structure. X‐ray scattering experiments refute the possibility of positional order, yet optical textures are consistent with a periodic structure. We suggest that the mesophase exhibited by this material is a new type of nematic‐like mesophase with some form of modulated structure. We find the NX phase to exhibit an electrooptic response consistent with a nematic‐like phase.

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“…Thermotropic nematics formed by achiral low molar mass mesogens constitute the structurally simplest liquid crystal (LC) phase and, to date, are the most widely used in electro-optic applications of LCs in the display technology. This nematic phase, hereafter denoted by NU, shows no long-range order of the molecular positions but is characterized by uniaxial apolar ordering of the molecular orientations about a unique 3 The discovery of the Nx phase initiated intensive, and still ongoing [32][33][34][35][36][37], investigations of its properties and thereby of its structure and distinction from other LC phases. It is now generally accepted that the orientational order in this phase is helically modulated with pitch on the order of 10 nm [23,38,39] and with the possibility of coexistence of both senses of helical twisting in different domains within an unbiased sample [20,40].…”

Section: Introductionmentioning

confidence: 99%

Molecular dynamics simulations of nematic phases formed by cyano-biphenyl dimers

Vanakaras

Photinos

2018

Liquid Crystals

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Molecular dynamics simulations of selected members of the cyano-biphenyl series of dimers (CBnCB) have been set up using atomistic detail interactions among intermolecular pairs of united atoms and allowing fully for the flexibility of the spacer chain. Detailed results are presented for the CB7CB dimers, showing an isotropic fluid phase and two nematic phases. The positional and orientational correlation functions extracted from the simulations are used to elucidate the structure of the low-temperature nematic phase. Polar molecular ordering is clearly identified along a direction undergoing helical twisting at right angles to the helical axis, with a constant pitch of about of 8nm. The local ordering of the various molecular segments is calculated and found to be in excellent agreement with experimental NMR measurements. Key findings of the simulation are shown to be correctly predicted by the theoretical model of the polar-twisted nematic (NPT) phase [A.G. Vanakaras, D.J. Photinos, Soft Matter. 12 (2016) 2208-2220]. The complete failure of the usual twist bend model (NTB) to account for these findings is demonstrated. 2 direction, represented by a unit vector n, the nematic phase "director". The uniaxiality of the phase implies full rotational symmetry (i.e. invariance of all the physical properties) about the director whilst the a-polarity of NU implies the physical indistinguishability of the directions n and -n. The lowest free energy state of the bulk NU phase corresponds to spatially uniform director field. Mild deformations of the director field, preserving the local symmetry of the phase and the degree of molecular ordering, give rise to elastic behavior of the bulk NU; three types of such director-field deformation are possible: bend, splay and twist. [1] Despite theoretical predictions suggesting the possibility of various deviations from the NU phase, corresponding to biaxial nematic phases (NB) [2], polar nematic phases, [3,4] uniaxial [5] (NPU) or biaxial[6] (NPB), spontaneous twist-bend (NTB) nematics [7], etc, the NU phase remained until recently the only stable thermotropic nematic phase that could be produced experimentally. Thus, unlike the rich polymorphism found in the smectic phases or in the columnar phases of LCs [8,9], all known thermotropic nematics belonged to the NU phase and its chiral counterpart (N*). Chiral nematic phases were known to be produced only by chiral mesogens. Such phases usually show spontaneous twist of the director n, with helical pitch often in the optical wavelength regime. Close to the isotropic phase (I) transition temperature, the helical structures may show three-dimensional topological order, leading to the blue phases (BPs).The above landscape of the nematic phase, comprising only liquid crystals of the NU phase, presently termed as "common nematics", and the chiral N* (also known as cholesteric), has changed significantly, and somehow surprisingly, as a result of novel experimental findings in the last 15 years: (i) The long predicted biaxial nematic phase ...

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Characterization of the Submicrometer Hierarchy Levels in the Twist-Bend Nematic Phase with Nanometric Helices via Photopolymerization. Explanation for the Sign Reversal in the Polar Response

Cited by 26 publications

References 32 publications

Metastable room-temperature twist-bend nematic phases via photopolymerization

Metastable room-temperature twist-bend nematic phases via photopolymerization

Pentaerythritol Derived Tetrapode Exhibiting a Nematic‐Like Mesophase at Ambient Temperatures

Molecular dynamics simulations of nematic phases formed by cyano-biphenyl dimers

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