Fast switching behaviour and dielectric parameters of two chiral ferroelectric mesogens

Nepal, Shantiram; Mondal, Sarmistha; Sinha, Anindita; Das, Bidisa; Das, Malay Kumar; Dmochowska, Ewelina; Herman, Jakub; Czerwiński, Michał

doi:10.1080/02678292.2020.1735547

Cited by 7 publications

(3 citation statements)

References 42 publications

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“…Polar anchoring is an electrostatic interaction, while dispersive anchoring is London or van der Waals interactions between LC molecules and the anchoring surface (in our case, a polymer layer) [ 82 , 83 ]. Anchoring energy coefficients, dispersion, W d , and polar, W p , can be calculated according to the formulas [ 80 , 84 , 85 ]:

where γ , d , τ , K , P s and E th are rotational viscosity, layer thickness, switching time, mean elastic constant, spontaneous polarization and threshold field for molecular reorientation, respectively. Due to the lack of the K value, it was not possible to determine the polar anchoring coefficient, W p .…”

Section: Resultsmentioning

confidence: 99%

Modifications of FLC Physical Properties through Doping with Fe2O3 Nanoparticles (Part I)

et al. 2021

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The aim of this paper is to show, by systematic studies, the influence of γ-Fe2O3 nanoparticles on the physical parameters of the liquid crystalline matrix, exhibiting a ferroelectric phase in a wide temperature range. The detailed research was carried out by using diffraction (PXRD), microscopic (OM, SEM, FCPM, POM), thermal (DSC), optical (TLI), electric and spectroscopic (FTIR) methods. We show that even the smallest concentration of γ-Fe2O3 nanoparticles largely modifies the parameters of the ferroelectric SmC* phase, such as spontaneous polarization, switching time, tilt angle, rotational viscosity, dispersion anchoring energy coefficient and helix pitch. The admixture also causes a significant reduction in the temperature of phase transitions, broadening the SmA* phase at the expense of the SmC* phase and strong streaking of the texture. We present and explain the non-monotonic modification of these parameters with an increase in the nanoparticle concentration. The influence of oleic acid admixture on these parameters is also widely discussed. We have shown that certain parameters of organic-metal nanocomposites can be controlled by the appropriate amount of metal admixture.

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Section: Resultsmentioning

confidence: 99%

Modifications of FLC Physical Properties through Doping with Fe2O3 Nanoparticles (Part I)

et al. 2021

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“…The temperature dependence of the parallel and perpendicular permittivity’s (ε || and ε ⊥ ) and their average value ε avg = (2ε ⊥ + ε || )/3 for the (Compound A + Compound B) system is shown in Figure 4 a–c, respectively. Figure 4 b shows that ε ⊥ values peak in the SmC* phase (~19–28); this enhanced value is due to the temperature-dependent fluctuations of molecules in the direction of the phase angle of the helical structure [ 69 , 70 , 71 , 72 , 73 , 74 , 75 ]. The increment of ε ⊥ is greater than ε || in the SmC* phase.…”

Section: Resultsmentioning

confidence: 99%

“…The value of P s decreases with an increase in the temperature and attains their lowest values at the SmC*-SmA* transition temperature. Spontaneous polarization reaches ~340 nC.cm −2 in the SmC A * phase (30 °C); this high value of Ps is due to the contribution from the bulky nature of the chiral unit of the compounds, large dipole moment of the ester linkage and the high (43° to 45°) tilt angle of molecules with respect to the smectic layer normal, which increases the rotational hindrance barrier [ 67 , 69 , 77 ]. On comparing the variation of molar concentration with P s of the Compound A + Compound B mixture system, P s of Compound B is ~190 nC.cm −2 (mole concentration, x = 0.0) and it increases with the increase in molar concentration of Compound A in the mixture.…”

Section: Resultsmentioning

confidence: 99%

Static Permittivity and Electro-Optical Properties of Bi-Component Orthoconic Antiferroelectric Liquid Crystalline Mixtures Targeted for Polymer Stabilized Sensing Systems

Nepal¹,

Das²,

Das

et al. 2022

Polymers

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The behavior of two newly formulated bi-component orthoconic antiferroelectric liquid crystalline (OAFLC) systems, i.e., the Compound A + Compound B mixture system and Compound C + Compound B mixture system has been discussed in light of temperature and concentration dependencies of helical pitch length, spontaneous polarization, relaxation time, bulk viscosity, and the anchoring energy strength coefficient, together with static dielectric permittivity (ε) and dielectric anisotropy. Compound A + Compound B mixtures possess spontaneous polarization between 190–340 nC.cm−2 and fast relaxation times between 190–320 µs in the smectic antiferroelectric SmCA* phase at room temperature. Compound C + Compound B mixtures also have a spontaneous polarization in the range of 190–280 nC.cm−2 and relaxation times in the range of 190–230 µs at room temperature. Most of the mixtures have a helical pitch below one micrometer in the SmCA* phase. These advanced mixtures show a broad temperature range of the antiferroelectric SmCA* phase, fast switching of molecules under an applied electric field, negative dielectric anisotropy and a short helical pitch, confirming the advantage of designing new polymer-stabilized OAFLC that is targeted for novel application in sensing devices, utilizing the fast responsive electro-optical modulation elements.

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Self-assembling behaviour of chiral calamitic monoacrylates targeted for polymer stabilisation of polar smectic phases in chiral liquid crystals

Dmochowska

Herman

Czerwiński

et al. 2021

Journal of Molecular Liquids

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Fast switching behaviour and dielectric parameters of two chiral ferroelectric mesogens

Cited by 7 publications

References 42 publications

Modifications of FLC Physical Properties through Doping with Fe2O3 Nanoparticles (Part I)

Modifications of FLC Physical Properties through Doping with Fe2O3 Nanoparticles (Part I)

Static Permittivity and Electro-Optical Properties of Bi-Component Orthoconic Antiferroelectric Liquid Crystalline Mixtures Targeted for Polymer Stabilized Sensing Systems

Self-assembling behaviour of chiral calamitic monoacrylates targeted for polymer stabilisation of polar smectic phases in chiral liquid crystals

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