Determination of Rotational Viscosity and Pretilt Angle in Nematic Liquid Crystals from Transient Current: Influence of Ionic Conduction

Imai, Masahiro; Naito, Hiroyoshi; Okuda, Masahiro; Sugimura, Akihiko

doi:10.1080/10587259508038671

Cited by 25 publications

(13 citation statements)

References 24 publications

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“…The transient current method [39,40] was used to obtain γ 1 for the nematic samples and the experimental details are mentioned elsewhere. [30] Figure 7(a) shows that γ 1 of the hybrid is lower than that of the pure LC -which explains the faster electro-optic response for the 5CB + graphene hybrid.…”

Section: Graphene-doped Nematic Lc: Faster Electrooptic Responsementioning

confidence: 99%

Graphene and liquid crystal mediated interactions

2016

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The two-dimensional graphene-honeycomb structure can interact with the liquid crystal's (LC) benzene rings through π-π electron stacking. This LC-graphene interaction gives rise to a number of interesting physical and optical phenomena in the LC. In this paper, we present a combination of a review and original research of the exploration of novel themes of LC ordering at the nanoscale graphene surface and its macroscopic effects on the LC's nematic and smectic phases. We show that monolayer graphene films impose planar alignment on the LC, creating pseudo-nematic domains (PNDs) at the surface of graphene. In a graphenenematic suspension, these PNDs enhance the orientational order parameter, exhibiting a giant enhancement in the dielectric anisotropy of the LC. These anisotropic domains interact with the external electric field, resulting in a non-zero dielectric anisotropy in the isotropic phase as well. We also show that graphene flakes in an LC reduce the free ion concentration in the nematic media by an ion-trapping process. The reduction of mobile ions in the LC is found to have subsequent impacts on the LC's rotational viscosity, allowing the nematic director to respond quicker on switching the electric field on and off. In a ferroelectric LC (smectic-C Ã phase), suspended graphene flakes enhance the spontaneous polarisation by improving the tilted smectic-C Ã ordering resulting from the π-π electron stacking. This effect accelerates the ferroelectric-switching phenomenon. Graphene can possess strain chirality due to a soft shear mode. This surface chirality of graphene can be transmitted into LC molecules exhibiting two types of chiral signatures in the LCs: an electroclinic effect (a polar tilt of the LC director perpendicular to, and linear in, an applied electric field) in the smectic-A phase, and a macroscopic helical twist of the LC director in the nematic phase. Finally, we show that a graphene-based LC cell can be fabricated without using any aligning layers and ITO electrodes. Graphene itself can be used as the electrodes as well as the aligning layers, obtaining an electro-optic effect of the LC inside the cell. P A 50 m P A Planar alignment 0 V 45 V Homeotropic alignment E ARTICLE HISTORY

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Section: Graphene-doped Nematic Lc: Faster Electrooptic Responsementioning

confidence: 99%

Graphene and liquid crystal mediated interactions

2016

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“…[19] The x value of a simple sandwich cell filled with the host nematic LC used in this study in homogeneous alignment was measured according to a reported method [20] and was found to increase gradually with decreasing temperature. It is reasonable to assume that the Kerr effect of PSBP should be dominated by the field-induced reorientation of the local director consist- ing of the cooperatively ordered molecules with a common orientational direction.…”

Section: Dynamics Of Lc Molecular Rotationmentioning

confidence: 99%

Low‐Temperature Properties of Polymer‐Stabilised Liquid‐Crystal Blue Phases

et al. 2014

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The temperature dependences of the Kerr coefficient and the response time in the electrooptical effect of polymer-stabilised blue phases (PSBPs) of liquid crystals (LCs) with various polymer concentrations are investigated in a wide temperature range including temperatures lower than room temperature. The Kerr coefficients are found to abruptly decrease at low temperature, and the response time-temperature relation obeys the Arrhenius equation. For comparison of the Kerr effect and molecular rotation at low temperature, various physical properties such as permittivity, rotational relaxation time and dielectric relaxation strength of the PSBPs are investigated. The electrooptical response times and the dielectric relaxation times show different temperature dependences, and rotation of LC molecules in PSBPs was sufficiently active at low temperature and not strongly affected by the polymer.

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“…The rotational viscosity for the nematic samples was obtained by measuring the transient current induced by a DC field across the planar-aligned cell configuration. [41][42][43] When a DC field (much higher than the threshold field) is applied across a planar LC cell, the induced transient current I(t) through the cell shows a time response as the nematic director undergoes planar to homeotropic orientational transition. The transient current response is given by [41][42][43] …”

Section: -mentioning

confidence: 99%

Evidence of nanodiamond-self-assembly in a liquid crystal, and the consequent impacts on the liquid crystal properties

et al. 2017

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A small quantity of nanodiamonds (NDs) was dispersed in a nematic liquid crystal (LC), and the NDs were found to exhibit an anisotropic self-assembly along the nematic director. The anisotropic assembly of the NDs in the LC matrix was probed by measuring the dielectric anisotropy, Δε, of the LC+ND system, which showed a significant increase in Δε. Additional studies revealed that the presence of NDs reduced the rotational viscosity and the pretilt angle of the LC. The studies were carried out with several ND concentrations in the LC and the experimental results coherently suggest that there exists an optimal concentration of ND. Above this optimal ND concentration, the anisotropic assembly of the NDs was found to be not effective anymore. The rotational viscosity and the pretilt angle of the LC were found to increase above the optimal concentration of ND.

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Determination of Rotational Viscosity and Pretilt Angle in Nematic Liquid Crystals from Transient Current: Influence of Ionic Conduction

Cited by 25 publications

References 24 publications

Graphene and liquid crystal mediated interactions

Graphene and liquid crystal mediated interactions

Low‐Temperature Properties of Polymer‐Stabilised Liquid‐Crystal Blue Phases

Evidence of nanodiamond-self-assembly in a liquid crystal, and the consequent impacts on the liquid crystal properties

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