Effect In Ferroelectric Liquid Crystals Research Articles

Bulk photovoltaic effect in ferroelectric nematic liquid crystals.

The bulk photovoltaic (BPV) effect in ferroelectric liquid crystals is of increasing scientific interest owing to its great potential for light-energy conversion. The ferroelectric nematic phase exhibits a huge spontaneous polarization that can be aligned to a preferred direction. In this Letter, we investigate the tensorial properties of the BPV effect in the planarly aligned ferroelectric nematic phase of the liquid crystalline material RM734. A steady-state short-circuit photocurrent of ~160 pA and an open-circuit photovoltage of ~50 mV were observed in a cell with a thickness of 5.5 µm under the illumination of ultraviolet light without any bias voltage. Based on the photocurrent measurements in different electrode configurations, the non-zero elements of the BPV tensor were obtained. The BPV effect is attributed to the combination of the spontaneous polarization and the asymmetric distribution of photoinduced charge carriers. This study not only provides an understanding of the bulk PV mechanism in soft ferroelectrics but also promises a wide range of unprecedented, to the best of our knowledge, benefits for light harvesting to engineer marketable photovoltaic devices.

Improvement of optical properties and memory effect in ferroelectric liquid crystal by incorporating core/shell CoFe2O4/ZnO nanocrystals

Improvement of optical properties and memory effect in ferroelectric liquid crystal by incorporating core/shell CoFe2O4/ZnO nanocrystals

Bulk photovoltaic effect in ferroelectric liquid crystals comprising of quinquethiophene and lactic ester units

Bulk photovoltaic effect in ferroelectric liquid crystals comprising of quinquethiophene and lactic ester units

Study of the electrocaloric effect in ferroelectric liquid crystals

ABSTRACTElectrocaloric effect (ECE) in two ferroelectric liquid crystalline (FLC) materials has been evaluated by mean of two indirect characterization methods: the photopyroelectric (PPE) technique and the polarization current reversal one. The obtained results show a good correspondence of the adiabatic temperature change associated with the ECE evaluated from both methods. This validates the possibility to use the PPE technique to investigate the ECE in FLCs. This study also demonstrates that FLCs can be used as electrocaloric material. More particularly, it shows that as for their solid homologous, liquid crystals displays more pronounced ECE in the vicinity of a first order transition than that measured near to second-order one.

Simulation of spatial phase light modulators based on the ferroelectric liquid-crystals

We studied the possibility for building zonal spatial phase light modulators employing quadratic electro-optical effect in ferroelectric liquid-crystals (FLC). This effect allows one to achieve modulation frequencies up to 1 KHz, but leads to a change in the ellipticity of the polarization state. We analyzed the influence of ellipticity modulation on the formation of vortex light fields by multi-pixel modulators with square configuration of cells and modulators of sector type. It was shown that for the considered FLC the resulting amplitude modulation does not have a principal essential effect and vortex light fields of good quality can be generated.

Light amplification by photorefractive ferroelectric liquid crystal blends measured at 532 nm and 638 nm

GRAPHICAL ABSTRACT

Spatial phase light modulator based on the ferroelectric liquid-crystals: possibility of the device construction

The work investigates the possibility for building of zonal spatial phase light modulators employing the quadratic electro-optic effect in ferroelectric liquid-crystals and capable of providing modulation frequencies up to 1 kHz. The study is made through the use of numerical simulation methods and experimental modulation characteristics

Photovoltaic Effects in Ferroelectric Liquid Crystals based on Phenylterthiophene Derivatives

Photovoltaic effects in ferroelectrics have attracted much attention due to their potential of generating a large open-circuit voltage. Recently, we focus on an anomalous photovoltaic effect in fer...

Reverse bistable effect in ferroelectric liquid crystal devices with ultra-fast switching at low driving voltage.

In this Letter, reverse bistable effect with deep-sub-millisecond switching time is first reported in ferroelectric liquid crystal (FLC) devices using a homogeneous photo-alignment technique. It is indicated by our experimental results that both the anchoring energy and the dielectric property of the FLC's alignment layer is critical for the existence of the reverse bistable effect. In addition, with the derived criteria of the reverse bistable effect, we quantitatively analyze the switching dynamics of the reverse bistable FLC and the transition condition between the traditional bistability and our presented reverse bistability. Moreover, the fabricated FLC device exhibits an ultra-fast switching of ∼160 μs and a high contrast ratio of 1000:1, both of which were measured at a low driving voltage of 11 V. The featured deep-sub-millisecond switching time is really advantageous for our presented reverse bistable FLC devices, which enables a significant quality improvement of the existing optical devices, as well as a wide range of new applications in photonics and display areas.

Application of Ferroelectric Liquid Crystals to Optical Devices

Liquid crystals (LCs) are attractive for optical devices, such as lenses because of their large birefringence and high response to external field. However, the low-speed response of nematic LCs often becomes an obstacle to the progress of LC devices. In this study, we research the lens effect of ferroelectric LC by using a voltage-gradient cell. As a result, it is found that in order to obtain the lens effect in FLC, the wide cell gap, the large tilt angle and/or the large birefringence of FLC materials are necessary to increase the birefringence variation under the gradient voltage in addition to the monostabilization of FLC media.

Latching operation in a tunable wavelength filter using Si sampled grating waveguide with ferroelectric liquid crystal cladding.

A tunable wavelength filter fabricated with a latching function is proposed. The proposed tunable wavelength filter consists of a silicon sampled grating waveguide and ferro-electric liquid crystal (FLC) cladding. The sampled grating waveguide in a silicon-on-insulator (SOI) wafer achieved narrower stop bands than that with the conventional uniform grating structure. Enhanced wavelength shift was also obtained due to the increased effect in FLC by using a thinner silicon core. Bistable switching operation with the fabricated device, which was latching without state-sustaining power, was successfully demonstrated. Its switching and latching characteristics are also reported.

Photorefractive effect in ferroelectric liquid crystals

In this paper, we review recent progress of research on the photorefractive effect of ferroelectric liquid crystals. The photorefractive effect is a phenomenon that forms a dynamic hologram in a material. The interference of two laser beams in a photorefractive material establishes a refractive index grating. This phenomenon is applicable to a wide range of devices related to diffraction optics including 3D displays, optical amplification, optical tomography, novelty filters, and phase conjugate wave generators. Ferroelectric liquid crystals are considered as a candidate for practical photorefractive materials. A refractive index grating formation time of 8–10 ms and a large gain coefficient are easily obtained in photorefractive ferroelectric liquid crystals.

Statistical theory of flexoelectric effect in ferroelectric liquid crystals

The presence of impurity ions in a ferroelectric liquid crystal produces significant modulation in its polarization profile. We investigate this modulation both by a molecular statistical approach and by a suitable Landau–Ginzburg type free energy model. The molecular statistical approach predicts a value of the induced dipole moment into a host chiral mesogen by the electric field of the ions. The Landau–Ginzburg (LG) approach is based mainly on the flexoelectric effect that is generated by the ions through their electric field. The LG model captures the flexoelectric part of the polarization created by the distortion of the nematic director through the electric field of the ions. Then, the conditions of the helical stability of the chiral state are also investigated in the presence of ionic distortion of the nematic field in a ferroelectric medium.

Critical behaviour of the smectic A*–C* phase transition and electroclinic effect of ferroelectric liquid crystals with terphenyl rigid core

The SmA*–SmC* phase transition was studied by measuring the temperature and electric field dependences of the optical tilt angle, the electric polarisation and the dielectric spectra collected in a wide frequency range. Critical behaviour of the phase transition was analysed by varying the length of the fluorinated part of the alkyl terminal chain and by differing fluorine substitution in the terphenyl core. Both tilt and polarisation show tricritical mean-field behaviour for all homologues with n > 2. Almost all coefficients that describe the SmA*–SmC* transition in the frame of the Landau theory were derived for homologue series. Double fluorine substitution in the central ring of the core seems to promote the ‘de Vries'-type smectic A*–C* phase transition with a little layer shrinkage. These well correspond with the lower tilt angle and smaller changes of the birefringence at the phase transition compared to the other homologues.

Piezoelectric and flexoelectric effects in ferroelectric liquid crystals

Flexoelectric and piezoelectric effects in ferroelectric liquid crystals (FLCs) have been studied. It is shown that nonlinear electromechanical coupling is determined by a local flexoelectric effect. Dependence of the parameters of nonlinearity of the flexoelectric effect on the parameter of phase transition from a paraelectric phase to a polar phase has been studied. Dependencies of flexoelectric and piezoelectric coefficients on the frequency of the mechanical vibrations have been studied.

Alumina nanoparticles find an application to reduce the ionic effects of ferroelectric liquid crystal

We observed that the doping of alumina nanoparticles (AL-NPs) has suppressed the undesired ionic effect in ferroelectric liquid crystals (FLCs). The pure and AL-NPs doped FLC cells were analysed by means of dielectric spectroscopy and electrical resistivity/conductivity measurements. Dielectric loss spectra confirmed the disappearance of the low-frequency relaxation peak, which appears due to the presence of ionic impurities in the FLC materials. The reduction of ionic effects has been attributed to the strong adsorption of ionic impurities on the surface of AL-NPs. The adsorption capability of AL-NPs has been studied with both the size and their concentration in FLC material. This study would be helpful to minimize the undesired ionic effects of LC-based display devices.

Influence of Photoconductivity on the Photorefractive Effect of Ferroelectric Liquid Crystal Mixtures

The influence of photoconductivity on the photorefractive effect of ferroelectric liquid crystals (FLCs) was investigated. Mixtures of phenylpyrimidine derivatives, a chiral dopant, and a viscosity reducer were used as host FLC materials and two types of photoconductive compounds and an electron acceptor compound were added. The photorefractive effect was evaluated using two-beam coupling experiments. It was found that the magnitude of the gain coefficient was affected by the difference between the mobility of the photoconductive compound and that of the electron acceptor.

Piezoelectric effect in ferroelectric liquid crystal: A review

The data in the literature and our results of studying the piezoelectric effect in ferroelectric liquid crystals are analyzed. The existing theories of this effect in liquid crystals are discussed. The parametric transformations of electromechanical oscillations in ferroelectric liquid crystals are considered.

Specific features of the switching and electro-optics of ferroelectric liquid crystals

Polar effects in ferroelectric liquid crystals are considered. The physical principles underlying the bistable and hysteresis-free electro-optical switching are discussed. A simple physical model and a technique for controlling high-frequency hysteresis-free switching are proposed.

Gateless Gating Model vs. Gated Pore Model: Phase Pinning of Guanidinium Toxins in Sodium Channels

Unlike the gated pore model, which assumes the existence of a movable gate within the molecule, the gateless gating model (H. R. Leuchtag, Voltage-Sensitive Ion Channels, Springer 2008) (VSIC) explains ion-channel gating as a phase transition. Under this model, the closed channel conformation imposed by the resting electric field is a compact, ordered phase with behavior, such as critical temperature, hysteresis, fractional dispersion exponent (constant phase angle) and Curie-Weiss law, similar to that of phases seen in ferroelectric liquid crystals (VSIC, pp. 355-383). In the absence of a toxin molecule, threshold membrane depolarization indirectly brings about a stochastic phase transition to a less ordered phase in which S4 segments expand by the mutual repulsion of their positively charged residues. The resulting wider pitch of permeation pathway α helices elastically linked to the S4s permits ion replacement in the interloop H bonds and the subsequent percolation of permeant ions through the channel (VSIC, 477f, 506f). With an externally applied tetrodotoxin (TTX) or analog molecule complexed in the channel, however, the ordered phase is pinned by the toxin, inhibiting the transition to the ion-conducting phase (VSIC, 76, 382f). Phase pinning by impurities is an established effect in ferroelectric liquid crystals. In the toxin, a guanidinium group, H2N+=C(NH2)2, a highly resonant, planar, positive ion, is active in pinning the closed phase. The fact that guanidinium is also found in ferroelectric crystals such as guanidinium aluminum sulfate hexahydrate suggests that TTX enhances the spontaneous polarization of the resting phase. This explanation by the gateless gating model of specific toxin action is based on physical principles; in contrast, the phrase “TTX blocks the pore” offered by the gated pore model is vague and at the macroscopic rather than molecular scale.