Transient currents in nematic liquid crystals

Sugimura, Akihiko; Matsui, Nobuyuki; Takahashi, Yutaka; Sonomura, Hajimu; Naito, Hiroyoshi; Okuda, Masahiro

doi:10.1103/physrevb.43.8272

Cited by 77 publications

(46 citation statements)

References 15 publications

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“…Of course, the presence of the ions is also responsible for the relaxation of the electrical current in the circuit containing the nematic cell submitted to a step-like external voltage. This problem has been considered in detail by several authors, by describing the nematic cell by means of equivalent circuits [8][9][10]. In this paper we want to reconsider this problem and to show that the circuital analysis is not very useful to determine the relaxation time of the current.…”

Section: Introductionmentioning

confidence: 99%

Ionic relaxation in nematic liquid crystal cells

et al. 2007

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We investigate the dependence of the relaxation time of the current flowing in a nematic cell submitted to an external dc voltage on the physical properties of the substrate. We show that previously presented analyses of the same problem are not very useful for practical applications. We compare our theoretical predictions with experimental data, and show that the agreement is rather good. The influence of the adsorption-desorption phenomenon on the relaxation time is also discussed.

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Section: Introductionmentioning

confidence: 99%

Ionic relaxation in nematic liquid crystal cells

et al. 2007

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“…In some cases, ions play an important role in the manipulation of devices, and in others, they are just impurities to be eliminated. In optical devices using liquid crystals (LCs), ions are usually unwanted impurities, which seriously deteriorate the reliability of the devices [4,5]. In particular, LC display (LCD) is very sensitive to ion impurities [6], which causes AC amplitude drop due to ion migration inside the LC layer and DC voltage shift due to the accumulation of migrated ions on surfaces.…”

Section: Introductionmentioning

confidence: 99%

Ionic impurity control by a photopolymerisation process of reactive mesogen

et al. 2013

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Extremely low ion density, 10 −8 −10 −11 molar fraction, which inevitably exists due to residual ion impurities even in a purified liquid crystal (LC) compound, can significantly influence the electro-optic response in LC devices. We found that the density of ionic molecules increased with the addition of various dopants including triphenylphosphine oxide (TPPO), molecules with the functional group of aldehyde, epoxide and so on into a nematic LC cell by observing the electrical response of the LC cells and that the irradiation of ultraviolet (UV) light accelerated the generation of ionic molecules, indicating degradation of organic materials. However, the addition of reactive mesogen (RM) compounds to the LC mixture significantly decreased the effective density of ions during and after the photopolymerisation process. The cured RM networks effectively captured the ion impurities during the photopolymerising process and their ion capturing ability was sustained even after completing the photopolymerisation process. This observation may provide a simple and useful way to control the effective ion density in a liquid medium down to extremely low levels.

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“…In the pioneering papers the analysis was mainly focused on the re-normalization of the anchoring energy and flexoelectric coefficients due to the presence of the ions, and limited to considering the static situation [22][23][24][25][26][27][28][29][30][31][32][33]. Investigations of the influence of ions on the dynamical properties of nematic samples have been presented by several groups, mainly for practical applications [34][35][36][37][38][39][40][41][42][43][44][45][46][47]. In the relevant theoretical analysis, the characteristic times are the diffusion time and the drift time [48].…”

Section: Introductionmentioning

confidence: 99%

Adsorption–desorption phenomenon and the kinetic equation at interfaces in liquid crystalline systems

Evangelista

Barbero

2006

Liquid Crystals

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The adsorption-desorption phenomenon in a sample having the shape of a slab is investigated by using a particular form for the kinetic equation at the limiting surfaces. A closed solution for the time evolution of the ion density in a nematic liquid crystal sample submitted to an external field is obtained in the limit in which the effective field coincides with the external field. In this framework it is shown that the intrinsic time connected with the presence of the electric field is proportional to the drift time. The constant of proportionality is of the order of the ratio between the thermal agitation energy and the electrostatic energy. In a similar manner, the time evolution of the bulk and surface densities, in the case of neutral particles, is also determined in a closed form by means of a simple expression. A microscopic model giving rise to a kinetic equation, similar to the one used in the analysis, is presented. We propose a statistical interpretation of the adsorption-desorption phenomenon in the framework of Maxwell-Boltzmann statistics, in which the relationship between the phenomenological parameters, entering into the kinetic equation at the boundary surfaces, with the microscopic model is derived. The analysis is suitable for the description of the adsorption phenomena of neutral particles (dyes) as well as charged particles (ions) in nematic liquid crystals.

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Transient currents in nematic liquid crystals

Cited by 77 publications

References 15 publications

Ionic relaxation in nematic liquid crystal cells

Ionic relaxation in nematic liquid crystal cells

Ionic impurity control by a photopolymerisation process of reactive mesogen

Adsorption–desorption phenomenon and the kinetic equation at interfaces in liquid crystalline systems

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