Measurement of Flexo-coefficients for Nematic LCs without the Influence of the Impurity Ions by Using the Chromatographic Isolation Method

Takahashi, Taiju; Nakamura, Shusuke; Kudoh, Yukihiro

doi:10.1080/15421406.2015.1030211

Cited by 1 publication

(2 citation statements)

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Section: Measurement Of Flexoelectric Coefficients Has Been Onementioning

confidence: 99%

“…The other is due to the indirect electro-optical measurement induced by the inverse flexoelectric effect. With regard to the former cause, there are some reports that the flexoelectric coefficients can be measured by avoiding the influence of impurities contained in the liquid crystal 5,6) .Solving the latter cause is inherently more complicated.Because, in general, flexoelectric coefficients is indirectly estimated through the electro-optical response due to the change of LC director distribution throughout the LC cell, which is seriously affected not only by flexoelectric effect but also by interfacial factors such as surface anchoring energy and pretilt angle. In other words, flexoelectric coefficients can be estimated by a numerical simulation based on the continuum theory that also considered the surface anchoring effect.…”

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[Paper] Estimation of Flexoelectric Coefficients by Means of Transmission Phase Difference of Nematic Liquid Crystal Cells

Kimura

Fujiwara

Ueno

et al. 2021

MTA

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Measurement of flexoelectric coefficients has been oneof the most difficult research subjects of liquid crystals (LCs). As described in the first literature published by R. B. Mayer 1) , flexoelectric polarization is emerged by orientational deformation called splay and bend 2) . Like piezoelectric polarization in crystals, flexoelectric polarization had seemed to be easily measurable bulk polarization. Up to today, various measurement methods have been proposed. For example, T. Takahashi et al. 3) and S. A. Jewell et al. 4) separately reported experimental measurement results of flexoelectric coefficients based on their original optical methods, where the obtained the sum of the splay and bend flexoelectric coefficients (e p = e11 + e33) were the order of 10 -11 C/m. However, it is known that even measurement results for de facto standard LC material such as 5CB (4'-pentyl-4biphenylcarbonitrile), reported flexoelectric coefficients obtained by different past measurement methods have not coincide its sign, to say nothing of its values 2) . There seems to be two major causes; one is that the induced polarization is sealed by ionic impurities. The other is due to the indirect electro-optical measurement induced by the inverse flexoelectric effect. With regard to the former cause, there are some reports that the flexoelectric coefficients can be measured by avoiding the influence of impurities contained in the liquid crystal 5,6) .Solving the latter cause is inherently more complicated.Because, in general, flexoelectric coefficients is indirectly estimated through the electro-optical response due to the change of LC director distribution throughout the LC cell, which is seriously affected not only by flexoelectric effect but also by interfacial factors such as surface anchoring energy and pretilt angle. In other words, flexoelectric coefficients can be estimated by a numerical simulation based on the continuum theory that also considered the surface anchoring effect. That is, in order to discuss the correctness of the estimation of flexoelectric coefficients, it is necessary to reexamine surface anchoring energy and pretilt angle at the orientational surface as well as bulk physical parameters such as dielectric constant and elastic constant.Previously, our group demonstrated unique measurement method to determine surface anchoring energy, pretilt angle, dielectric anisotropy and reduced elastic constant simultaneously by means of the symmetric oblique incident transmission ellipsometry (SOITE) 7, 8) . As an application of SOITE method, we also tried to estimate the flexoelectric coefficients 9, 10) . However, it seemed that the expected accuracy and reproducibility have not been obtained so far because of Abstract Improvement of the flexoelectric coefficients estimating procedure by means of the transmission phase difference measurement was demonstrated. It was found that the sign of the sum of two flexoelectric coefficients for splay and bend deformation can be determined from the DC applied voltage dependence cu...

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Section: Measurement Of Flexoelectric Coefficients Has Been Onementioning

confidence: 99%

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confidence: 99%