Photo-driven giant reduction of the Frank elastic constants in a bent-core nematic liquid crystal

Madhuri, P. Lakshmi; Prasad, S. Krishna; Hiremath, Uma S.; Yelamaggad, C. V.

doi:10.1063/1.4885041

Cited by 13 publications

(10 citation statements)

References 26 publications

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“…Figure 9 presents the thermal dependence of the splay elastic constant for HLC and the nanocomposite. For both materials, K 11 exhibits a monotonic variation with temperature, a standard feature seen for rod-like bent core as well as the soft-bent compounds [12][13][14][15][16][17]22,23,26,27]. However, addition of ZnO NRs increases the magnitude of K 11 by as much as 46% at the lowest temperature measured.…”

Section: Frank Elastic Constantsmentioning

confidence: 83%

“…The inner surfaces of the substrates have a polymer layer to promote a unidirectional planar alignment of the LC molecules. Permittivity and elastic constant measurements were performed at a constant frequency of 10 kHz using a high precision LCR meter (Agilent 4284A) capable of applying an oscillating voltage up to 20 V. The procedure, based on the Deuling analysis [20,21], was implemented by a userwritten routine scripted in MATLAB [22,23]. Figure 5 shows the DSC profiles obtained at a rate of 5…”

Section: Methodsmentioning

confidence: 99%

“…The sample capacitance was used to detect and measure this change. Using V th and ε, the splay (K 11 ) and bend (K 33 ) elastic constants are calculated using the Deuling analysis [20][21][22][23]. The actual expressions employed are…”

Section: Frank Elastic Constantsmentioning

confidence: 99%

“…Here, ε 0 is the permittivity of free space, κ = (K 33 /K 11 ) − 1, γ = (ε /ε ⊥ ) − 1 and φ m is the angle between the director and the walls of the substrate with φ m being the value in the midplane of the sample. The value of K 11 can be directly obtained through equation (2) with the help of experimentally determined V th and ε values, whereas extraction of K 33 requires a full profile fitting to equation (3), carried out with the help of a MATLAB script [22,23]. The profiles of capacitance vs. applied voltage V obtained for HLC and the HLC1Z composite at several temperatures are shown in figure 8a and b, respectively.…”

Section: Frank Elastic Constantsmentioning

confidence: 99%

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Influence of zinc oxide nanorods on an orientationally ordered fluid comprising soft-bent dimers

et al. 2018

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Bent-core liquid crystals (LCs) introduced a whole new dimension to the science of LCs. Besides re-emphasizing the importance of the shape of the molecule, they brought in phases with symmetry, not known earlier. Another sub-class of systems that is emerging is that of soft-bent molecules. In contrast with the bent-core molecules, here the bend is achieved through the parity of the aliphatic linker that connects two monomers. They hold the unique advantage that a simple variation of temperature can favour different conformer states and thus govern the self-assembled structure. A highlight of the power of this route is seen in terms of the discovery of a new type of nematic, viz., twist-bend nematic. Investigations on not only this phase but also the regular nematic that often precedes it have received significant attention in the last few years. Here we present results on the regular nematic phase of a binary mixture comprising such a soft-bent dimer, known in the literature as CB7CB, by incorporating zinc oxide nanorods (NRs) into the system. The NRs with an aspect ratio of ∼7.2, not very different from that of LCs, further accentuate the importance of shape and shape anisotropy of the entities. Specifically, we observe that the nematic-isotropic transition temperature increases by ∼1.9 K even for a low concentration of 4% NRs. While the dielectric anisotropy decreases, birefringence shows a substantial increase, adding to the complexity of the influence. Upon addition of minute amount of NRs (1%), while the splay elastic constant gets enhanced, its bend counterpart not only gets reduced but retains the convex-shaped thermal profile seen for the parent mixture.

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Section: Frank Elastic Constantsmentioning

confidence: 83%

Section: Methodsmentioning

confidence: 99%

Section: Frank Elastic Constantsmentioning

confidence: 99%

Section: Frank Elastic Constantsmentioning

confidence: 99%

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Influence of zinc oxide nanorods on an orientationally ordered fluid comprising soft-bent dimers

et al. 2018

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“…Hence we restrict the discussion to the results in the N phase. The profiles were analyzed using procedure described earlier, which is based on the continuum description of the Freedericksz behavior by Deuling, , the procedure is briefly recalled here. Under equilibrium conditions the LC molecules, contained in a sandwich type cell, are oriented parallel to the substrate surface in a uniform planar manner.…”

Section: Resultsmentioning

confidence: 99%

Effect of Pressure on Dielectric and Frank Elastic Constants of a Material Exhibiting the Twist Bend Nematic Phase

et al. 2017

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We report the first investigation on the effect of applied pressure on the now well-known dimer α,ω bis(4,4'-cyanobiphenyl)heptane (CB7CB) that exhibits two types of nematic: the regular uniaxial nematic (N) and the recently discovered twist-bend nematic (N) phase. At atmospheric pressure, the thermal behavior of ε, the permittivity normal to the director in the N phase decreases on entering the N wherein the value represents permittivity orthogonal to the helical axis. Application of pressure initially decreases the magnitude of the change in ε and with further increase in pressure exhibits an increase in the value. Such a change in the feature of ε is similar to that obtained at room pressure when the monomeric heptyloxy cyanobiphenyl (7OCB) is doped to CB7CB at a high concentration of 50%. The dielectric anisotropy exhibits a trend reversal with temperature, the extent of which is affected at high pressures. Another salient feature of the study is the effect that pressure has on the Frank bend elastic constant K. Over the pressure range studied K enhances by a large factor of 5. In contrast, the splay elastic constant exhibits a much smaller change of only 70%. The pressure-temperature phase boundary has a much smaller slope for the N-N transformation than for the isotropic-N transition. We propose that all these features can be understood in terms of the relative population of the more energetic horseshoe and lower energy extended conformer adopted by the CB7CB molecule. The extended conformer is favored at lower temperatures or at higher pressures. This argument is validated by X-ray diffraction experiments at atmospheric pressure on the binary mixture of CB7CB and 7OCB, mentioned above.

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Measurement of Liquid Crystal Parameters and Physical Properties

Singh

2024

Handbook of Liquid Crystals—Volume I

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Photo-driven giant reduction of the Frank elastic constants in a bent-core nematic liquid crystal

Cited by 13 publications

References 26 publications

Influence of zinc oxide nanorods on an orientationally ordered fluid comprising soft-bent dimers

Influence of zinc oxide nanorods on an orientationally ordered fluid comprising soft-bent dimers

Effect of Pressure on Dielectric and Frank Elastic Constants of a Material Exhibiting the Twist Bend Nematic Phase

Measurement of Liquid Crystal Parameters and Physical Properties

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