Ionic transport effects in SSFLC cells

Zou, Zheguang; Clark, Noel A.; Handschy, Mark A.

doi:10.1080/00150199108217619

Cited by 41 publications

(18 citation statements)

References 3 publications

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“…[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. To understand the reduction in γ 1 , the presence of free ions in the pure 5CB and 5CB + graphene hybrid was measured by detecting the ion-bump [41] of a transient current generated by inverting the voltage at opposite electrodes in the LC cell. Figure 7(b) shows the ion concentration, n i , as a function of temperature in the nematic phase for 5CB and 5CB + graphene.…”

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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“…The importance of ions in smectic materials has been recognized early on [7][8][9] and there are many reports in the literature about experimental work and theoretical simulations of ion transport [7][8][9][10][11]. In smectic materials the electric field generated by the ions can play an important role in the switching and the bistability of smectic devices.…”

Section: Introductionmentioning

confidence: 99%

Ion Transport and Switching Currents in Smectic Liquid Crystal Devices

Neyts

Beunis

2006

GFER

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In SSFLC and AFLC devices, the voltage over the liquid crystal is not only determined by the applied voltage, but also by the separation of ions and the spontaneous polarization. The motion of ions and the switching of the spontaneous polarization are therefore interfering phenomena. A simplified model for ion transport and switching of polarization is introduced which is able to explain the shift in apparent threshold voltage and the variation of the hysteresis width.

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“…A remaining challenge for bistable FLC cells is that the range of drive conditions and temperature over which good alignment is maintained [26,27] must be expanded in order to be ready for commercial use. Also, this investigation has focused on the static or quasistatic bistable switching characteristics of FLC cells; a more complete understanding may require the inclusion of dynamics such as the formation and propagation of up and down domain walls [28], viscosities and flow [24,29,30], and ionic conductivity of the FLC layer due to impurities [22,23,[31][32][33][34]. In addition, because its effects grow as E 2 , dielectric anisotropy [omitted in Eq.…”

Section: Summary and Discussionmentioning

confidence: 99%

Polarization-stiffened ferroelectric liquid crystals: A thickness-independent bistable switching voltage with a lower limit of about 2 V and the transition to thresholdless switching

O’Callaghan¹

2015

Phys. Rev. E

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Typical ferroelectric Sm-C(*) liquid crystal (FLC) cells exhibit a voltage threshold for switching from one stable state to another despite the FLC's response being inherently continuous and thresholdless (free rotation of the director around the tilt cone). This switching threshold is due to FLC-surface interactions and to the chevron smectic structure commonly formed in cells. It is shown here that the FLC electrostatic energy contribution ∼P(S)(2) responsible for thresholdless switching of high-P(S) FLCs also plays a key role in the bistable switching of lower-P(S) FLCs. Among the consequences are that it can be difficult to lower a cell's threshold below V(TB)∼3.4(B/ɛ(F))(1/2) (B and ɛ(F) are the FLC's elastic and dielectric constants), that a cell's threshold becomes independent of cell thickness once it substantially exceeds the characteristic length ξ(P)=(ɛ(F)B)(1/2)/P(S), and that there are conditions under which alignment layer capacitance can decrease rather than increase the threshold (i.e., transition to thresholdless switching). A model that predicts and explains these behaviors is presented along with threshold measurements of representative FLC cells.

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Ionic transport effects in SSFLC cells

Cited by 41 publications

References 3 publications

Graphene and liquid crystal mediated interactions

Graphene and liquid crystal mediated interactions

Ion Transport and Switching Currents in Smectic Liquid Crystal Devices

Polarization-stiffened ferroelectric liquid crystals: A thickness-independent bistable switching voltage with a lower limit of about 2 V and the transition to thresholdless switching

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