Effect of molecular structure on dielectric and electro-optic properties of chiral liquid crystals based on lactic acid derivatives

Barman, Barnali; Das, Bidisa; Das, Malay Kumar; Hamplová, Věra; Bubnov, Alexej

doi:10.1016/j.molliq.2019.03.071

Cited by 35 publications

(5 citation statements)

References 74 publications

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“…In continuation of our previous investigations on the molecular structure-property correlations of a few chiral ferroelectric compounds from mesomorphic, electro-optic and static dielectric measurements [16], in this work we report the dielectric spectroscopy measurements on these compounds. As reported by us earlier [16], variations within the structural organization of the molecules has resulted in a rich polymorphism with multiple chiral variants including the chiral nematic N* phase, paraelectric orthogonal smectic A* phase and ferroelectric tilted smectic C* phase which are thermodynamically stable over a comparatively large range of temperature. Dielectric spectroscopy of ferroelectric systems provides a powerful insight into the dynamic aspects of these molecules which predetermine their applicability for different practical purposes [17][18][19][20][21][22].…”

Section: Introductionmentioning

confidence: 90%

“…Y denotes the linking group between first and second aromatic rings counting from the non-chiral part and the lateral substitution is indicated by Z. The details of the studied materials including the mesomorphic behaviour have already been presented in our previous publications [16,[33][34][35]. Table 1.…”

Section: Methodsmentioning

confidence: 99%

“…), clearing points (c.p.) and N* /SmA* to SmC* transition temperatures, of all the studied compounds as determined from polarising optical microscopy (POM) and checked by Differential Scanning Calorimetry (DSC) measurements [16] has been shown in Table 2.…”

Section: Phase Behaviourmentioning

confidence: 99%

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Dielectric Properties of Chiral Ferroelectric Liquid Crystalline Compounds with Three Aromatic Rings Connected by Ester Groups

Das

Barman

Das³

et al. 2019

Crystals

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The tilted ferroelectric SmC* phase of three structurally different series having three aromatic rings in the core structure connected by ester groups with different end alkyl chain lengths, all of which are derived from lactic acid, have been observed by broadband dielectric spectroscopy. Introduction of structural variations within the liquid crystalline compounds has led to the formation of chiral nematic N*, or the paraelectric orthogonal SmA* phase at higher temperatures. The dielectric spectra strongly depend both on the temperature as well as the specific molecular structure of the self-assembling compounds possessing the ferroelectric polar order. The results reveal a strong Goldstone mode in the ferroelectric SmC* phase with ~kHz relaxation frequency. In the SmC* phase, the real and imaginary parts of the complex permittivity increase up to certain temperature near the SmC*-N*/SmA* transition and then decrease with increasing temperature, perhaps due to the disruption of the molecular domains at the onset of the SmA*/N* phase transition. The dielectric strength attains a maximum value in the SmC* phase and then decreases near the SmA*/N* phase transition. The dielectric strength is also influenced by the lengths of the alkyl chain and the nature of the connecting unit of the constituent molecules. The relaxation time and the relaxation frequency are found to vary with the molecular structure of the studied ferroelectric compounds.

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Section: Introductionmentioning

confidence: 90%

Section: Methodsmentioning

confidence: 99%

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Dielectric Properties of Chiral Ferroelectric Liquid Crystalline Compounds with Three Aromatic Rings Connected by Ester Groups

Das

Barman

Das³

et al. 2019

Crystals

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“…After the ferroelectricity in liquid crystals was discovered in 1975 [1], many books and articles were written about synthesis, studies and application of new compounds having such properties [2][3][4][5][6][7][8][9][10][11][12]. Since then, many compounds have been synthesized and new materials on their basis were prepared and tested [13][14][15][16][17][18][19][20][21]. FLCs are characterized by fast electro-optical response, low driving voltage and memory effects, which make them suitable candidates for many advanced applications, such as displays, gratings or sensors [22][23][24][25].…”

Section: Introductionmentioning

confidence: 99%

New Ferroelectric Liquid Crystalline Materials with Properties Suitable for Surface Stabilized and Deformed Helix Effects

Czerwiński¹,

Tykarska²,

Kula³

2021

Liq. Cryst. and their Appl.

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Liquid crystals (LC) are widely used in optical devices. New electro-optic effects are still being established. The requirements of such devices increases thus still new materials are elaborated for such purpose. In this review, two electro-optic effects are described, namely Surface Stabilized Ferroelectric LC (SSFLC) and Deformed Helix Ferroelectric LC (DHFLC) effects. New ferroelectric liquid crystal mixtures were formulated which can be used in devices operating on the basis of the mentioned electro-optic effects. Two ways of mixture preparation have been used: mixing of chiral components or mixing of achiral components with addition of a small amount of chiral dopant. The ferroelectric mixtures with very short (less than 200 nm) or very long (more than 1 μm) pitches are discussed. The mixtures meet almost all requirements of SSFLC and DHFLC effects and therefore, have important prospects for applications in optical sensors.

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“…The self-organization structure of such compounds, and hence their favorable electro-optic, structural, and dielectric properties, can be adjusted by a proper design of molecular architecture build up from various units [15,[19][20][21][22][23][24]. Chiral liquid crystals derived from the lactic acid are intensively investigated due to definite advantages [19,25,26] with respect to other types of chiral molecular structures: chemical stability -no aging, reasonably low price, and a comprehensive variety of conventional and frustrated nematic and smectic phases stable in a broad temperature range. LC compounds with chiral part based on lactate group are actively used as: (i) chiral dopants while designing binary [27][28][29] and multicomponent functional mixtures [30,31]; (ii) reactive mesogens for macromolecular compounds used as side-chains for polymers [32][33][34] and elastomers [35,36]; (iii) functional dopants for organic photovoltaic cells [37][38][39] and matrices [40][41][42] for design of nanocomposite systems; and (iv) source of chirality for photosensitive low molar mass [21,[43][44][45] and macromolecular [20,34,[46][47][48] materials.…”

Section: Introductionmentioning

confidence: 99%

Self-Assembling Behavior of Smart Nanocomposite System: Ferroelectric Liquid Crystal Confined by Stretched Porous Polyethylene Film

et al. 2020

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The control and prediction of soft systems exhibiting self-organization behavior can be realized by different means but still remains a highlighted task. Novel advanced nanocomposite system has been designed by filling of a stretched porous polyethylene (PE) film with pore dimensions of hundreds of nanometers by chiral ferroelectric liquid crystalline (LC) compound possessing polar self-assembling behavior. Lactic acid derivative exhibiting the paraelectric orthogonal smectic A* and the ferroelectric tilted smectic C* phases over a broad temperature range is used as a self-assembling compound. The morphology of nanocomposite film has been checked by Atomic Force Microscopy (AFM). The designed nanocomposite has been studied by polarizing optical microscopy (POM), differential scanning calorimetry (DSC), small and wide-angle X-ray scattering and broadband dielectric spectroscopy. The effect of a porous PE confinement on self-assembling, structural, and dielectric behavior of the chiral LC compound has been established and discussed. While the mesomorphic and structural properties of the nanocomposite are found not to be much influenced in comparison to that of a pure LC compound, the polar properties have been toughly suppressed by the specific confinement. Nevertheless, the electro-optic switching was clearly observed under applied electric field of low frequency (210 V, 19 Hz). The dielectric spectroscopy and X-ray results reveal that the helical structure of the ferroelectric liquid crystal inside the PE matrix is completely unwound, and the molecules are aligned along stretching direction. Obtained results demonstrate possibilities of using stretched porous polyolefins as promising matrices for the design of new nanocomposites.

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Effect of molecular structure on dielectric and electro-optic properties of chiral liquid crystals based on lactic acid derivatives

Cited by 35 publications

References 74 publications

Dielectric Properties of Chiral Ferroelectric Liquid Crystalline Compounds with Three Aromatic Rings Connected by Ester Groups

Dielectric Properties of Chiral Ferroelectric Liquid Crystalline Compounds with Three Aromatic Rings Connected by Ester Groups

New Ferroelectric Liquid Crystalline Materials with Properties Suitable for Surface Stabilized and Deformed Helix Effects

Self-Assembling Behavior of Smart Nanocomposite System: Ferroelectric Liquid Crystal Confined by Stretched Porous Polyethylene Film

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