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In this article, we investigate the spontaneous emission properties of radiating molecules embedded in a chiral nematic liquid crystal, under the assumption that the electronic transition frequency is close to the photonic edge mode of the structure, i.e. at resonance. We take into account the transition broadening and the decay of electromagnetic field modes supported by the so-called `mirror-less' cavity. We employ the Jaynes-Cummings Hamiltonian to describe the electron interaction with the electromagnetic field, focusing on the mode with the diffracting polarization in the chiral nematic layer. As known in these structures, the density of photon states, calculated via the Wigner method, has distinct peaks on either side of the photonic band gap, which manifests itself as a considerable modification of the emission spectrum. We demonstrate that, near resonance, there are notable differences between the behavior of the density of states and the spontaneous emission profile of these structures. In addition, we examine in some detail the case of the logarithmic peak exhibited in the density of states in 2D photonic structures and obtain analytic relations for the Lamb shift and the broadening of the atomic transition in the emission spectrum. The dynamical behavior of the atom-field system is described by a system of two first order differential equations, solved using the Green's function method and the Fourier transform. The emission spectra are then calculated and compared with experimental data., Comment: 7 Figures, 12 References, 2 Appendices

Diverse functionalities of liquid crystals (LCs) offer enormous opportunities for their potential use in advanced mobile and smart displays, as well as novel non-display applications. Here, we present snapshots of the research carried out on emerging applications of LCs ranging from electronics to holography and self-powered systems. In addition, we will show our recent results focused on the development of new LC applications, such as programmable transistors, a transparent and active-type two-dimensional optical array and self-powered display systems based on LCs, and will briefly discuss their novel concepts and basic operating principles. Our research will give insights not only into comprehensively understanding technical and scientific applications of LCs, but also developing new discoveries of other LC-based devices. © 2014 by the authors.

A hybrid liquid crystal and carbon nanotube-based device which shows the capacity to perform as a switchable diffraction grating is demonstrated. A liquid crystal layer was sandwiched between two electrodes (patterned into gratings). The bottom electrode consists of a two dimensional square array of carbon nanotubes, while the top electrode comprises an ITO-based in-plane switching electrode on glass. The carbon nanotubes, due to their high aspect ratios, produce defects within the liquid crystal layer, producing a two dimensional grating. The device displays distinct voltage-dependent diffraction patterns due to the two different electrodes. The diffraction patterns are studied both computationally and experimentally, with good agreement between the results obtained. Both the diffraction pattern and efficiency from the device could be switched by varying the applied voltage across the liquid crystal layer. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Electro-optic switching in short-pitch polymer stabilized chiral nematic liquid crystals was studied and the relative contributions of flexoelectric and dielectric coupling were investigated: polymer stabilization was found to effectively suppress unwanted textural transitions of the chiral nematic liquid crystal and thereby enhance the electro-optical performance (high optical contrast for visible light, a near ideal optical hysteresis, fast electro-optic response). Test cells were studied that possessed interdigitated electrodes to electrically address the liquid crystal. Based on simulations, a well-fitted phenomenological description of the electro-optic response was derived considering both flexoelectro-optic and Kerr-effect based electro-optic response. © 2014 AIP Publishing LLC.

Active laser arrays, of arbitrary pattern, were created by inkjet deposition of self-assembled photonic structures in the form of dye-doped chiral nematic liquid crystals. The print process itself achieves the requisite alignment for photonic band-edge lasing action normal to the substrate; laser threshold and linewidth characteristics are presented.

We demonstrate modulations of electrical conductance and hysteresis behavior in ZnO nanowire transistors via electrically polarized switching of ferroelectric liquid crystal (FLC). After coating a nanowire channel in the transistors with FLCs, we observed large increases in channel conductance and hysteresis width, and a strong dependence of hysteresis loops on the polarization states associated with the orientation of electric dipole moments along the direction of the gate electric field. Furthermore, the reversible switching and retention characteristics provide the feasibility of creating a hybrid system with switch and memory functions. © 2013 American Institute of Physics.

A promising approach to the fabrication of materials with nanoscale features is the transfer of liquid-crystalline structure to polymers. However, this has not been achieved in systems with full three-dimensional periodicity. Here we demonstrate the fabrication of self-assembled three-dimensional nanostructures by polymer templating blue phase I, a chiral liquid crystal with cubic symmetry. Blue phase I was photopolymerized and the remaining liquid crystal removed to create a porous free-standing cast which retains the chiral three-dimensional structure of the blue phase, yet contains no chiral additive molecules. The cast may in turn be used as a hard template for the fabrication of new materials. By refilling the cast with an achiral nematic liquid crystal, we created templated blue phases which have unprecedented thermal stability in the range -125 to 125 [degrees symbol]C, and that act both as mirrorless lasers and switchable electro-optic devices. Blue-phase templated materials will facilitate advances in device architectures for photonics applications in particular., Comment: 14 pages, 4 figures. Postprint. Reviewed and accepted version of manuscript, not copyedited or in Nature Materials journal format. Supplementary information freely available at http://dx.doi.org/10.1038/nmat3330

Mixtures of two proprietary low molar mass organosiloxane liquid crystals were studied in order to improve their alignment and optimize their electro-optic properties for telecommunication applications. Over a certain concentration range, mixtures exhibited an isotropic-chiral smectic A-chiral smectic C (Iso-SmA*-SmC*) phase sequence leading to exceptionally good alignment. At room temperature, the spontaneous polarization of these samples was reduced from 225 nC cm-2 in the pure SmC* liquid crystal to as low as 75 nC cm-2 in the mixture. Within this concentration range, the ferroelectric tilt angle could be varied between 35° and 15° , while the rise time decreased by 69.4%. The rise times were

We describe wide temperature range bimesogenic chiral nematic liquid crystals mixtures with high flexoelectro-optic coefficients (e/K), of the order of 2.0–4.0 CN−1 m−1, with 50–100μs response times. Gray scale devices in both the ULH texture, with an optimum optical in plane switch of 45° at fields of

We report an on-chip integrated ferroelectric liquid crystal (FLC) waveguide structure suitable for telecommunication applications. Single gaps with different widths of 5, 10, and 20 μ m inside individual silica waveguides were filled with an FLC mixture. The waveguide devices operate as a binary switch or an attenuator in a temperature range from 30 ° C to 60 ° C. The FLC mixture exhibited a good alignment quality in these gaps without alignment layers. A good extinction ratio of up to 33.9 dB and a low insertion loss of

Wide-band tunability, large coherence-area, and in some cases multidirectional emission have made liquid-crystal lasers an attractive light source for applications like miniature medical diagnostic tool and large-area holographic laser displays. This article discusses the scientific origins of the technology of liquid-crystal lasers and reviews the current cutting-edge research.

Presently, nematic polymer dispersed liquid crystals (PDLCs) that are used in switchable glazing technology require constant power to operate and, moreover, exhibit unwanted haze at wide viewing angles. In this paper, a novel switchable glazing technology, based around a bistable electro-optic effect in the Smectic A liquid crystal phase, is described which does not require constant power to operate or exhibit haze. The application of a low-frequency (100 Hz) voltage induces an optically opaque state due to the motion of ionic material whereas the application of a higher frequency AC (1 kHz) voltage induces a haze-free clear state. Multistable (greyscale) operation is possible through the application of intermediate frequencies or voltages; the threshold voltages of the effect were found to range from 36 to 66 V rms. Any voltage-induced state is preserved indefinitely after removal of the voltage leading to low power consumption.

In this paper, we consider the electro-optic properties of a bistable display device based upon the smectic A phase which can function without polarizers. This scheme is attractive for low-power, high-efficiency devices with indefinite storage. The bistable modes are opaque (write), due to electrohydrodynamic instabilities from motion of ionic dopant at dc/low ac frequencies, and clear (erase), due to dielectric reorientation. The two regimes are delimited by a critical frequency at which ionic motion is damped out. From consideration of current flow through the cell and contrast ratio, it is shown that the display lifetime is significantly dependent on the write mode drive frequency e.g. operation at 100 Hz extends lifetime by a factor greater than 102 compared with 1 Hz. The origin of the limited lifetime at dc/low ac applied fields is explained via an electrolytic purification mechanism; operation at frequencies above a threshold (e.g. 50 Hz) significantly reduces this process. It is also proposed that, although this phenomenon must be minimized for dynamic scattering, the technique should be of benefit generally for in situ purification of liquid crystalline samples in other electro-optic effects where ionic conductivity is an undesirable property.

In this paper, we investigate the dependence of the bistable electro-optic response of organosiloxane based smectic A liquid crystals on key material properties; the modes are optically scattering ( 1 kHz), respectively. The scattering mode is generated by motion of doped ionic species and is dependent upon the conductivity anisotropy of the liquid crystal; the clear mode occurs through dielectric coupling at frequencies sufficient to inhibit ionic conduction. The pure siloxane liquid crystals exhibit unusually high anisotropic ionic conductivities; the ratio of the components parallel and perpendicular to the director is up to 0.005; for analogous non-siloxane based liquid crystals the value is ~0.5. However, the pure materials possess low dielectric anisotropy compared with similar polar liquid crystals, e.g. 0.8 compared with 8.4. Based upon these observations, we prepare exemplar mixtures of organosiloxane with 4-(ω-pentyloxy)-4'-cyanobiphenyl (5OCB) as a dielectric additive. These systems show beneficial properties: highly anisotropic conductivity coupled with an increase in the dielectric anisotropy. As a result, the electro-optic responses of these mixtures show a significant improvement upon the pure compounds; for example, for the 49% w/w mixture it is found that the response time of the optically clear mode is significantly reduced, e.g. from 130 ms (at 280 V rms) to 5 ms at an applied voltage of 102 V rms. We conclude that simple mixtures, using an organosiloxane as the bulk component, have much promise for use in bistable, electro-optic storage and display devices.

While we are all familiar with liquid crystal displays, an industry currently worth more than $60 billion yr −1 and growing rapidly, fewer people are aware of the breadth of the subject of liquid crystals—one that represents the study of the fourth state of matter. Liquid crystals are found as essential elements in biological systems, soaps and detergents, sensor technologies and in the manipulation of electromagnetic radiation of various wavelengths. This meeting was designed to highlight both the truly multidisciplinary nature of liquid crystal science and to feature those areas away from electro-optic displays; these issues are developed and summarized in more detail.

Lasers were invented some 40 years ago and are now used in a plethora of applications. Stable liquid crystals were discovered at about the same time, and are now the basis of a large display industry. Both technologies involve photonics, the former in the creation and use of light and the latter in the control and manipulation of light. However, it is only recently that these two mature technologies have been combined to form liquid-crystal lasers, heralding a new era for these photonic materials and the potential for novel applications. We summarize the characteristics of liquid crystals that lead to laser devices, the wide diversity of possible laser systems, and the properties of the light produced.

We demonstrate three electro-optic telecommunication devices operating at a wavelength λ = 1550 nm: an optical switch or modulator, a variable attenuator, and a rotatable waveplate. These devices make use of the electroclinic and ferroelectric properties of a chiral smectic organosiloxane liquid crystal. Under moderate electric fields of ≤23 V/μm we observed an optical power modulation of up to 38 dB and a switching time of ∼100 μs. The waveplate could be continuously rotated over 38°. We also present birefringence data of this liquid crystal at λ = 1550 nm as a function of temperature and the implications on the development of liquid crystal telecommunication devices.

The effect of altering the excitation rate on the emission energy of a photonic band edge liquid crystal laser has been investigated. The results showed that for excitation energies greater than 18 µJ/pulse, an increase in the excitation rate from 1 to 20 Hz caused a reduction in the total emission energy of the photonic band edge liquid crystal laser of up to 90%. In order to establish the cause of this reduction several factors were considered: dye bleaching, thermal/density effects and director-axis reorientation (either by virtue of a light-induced torque or other effects such as a flow-induced orientational decay). Although some dye bleaching was observed, the main factor responsible for the reduction in the overall emission efficiency was found to be nonlinear changes in the director-axis reorientation. Furthermore, our results suggest that the director-axis reorientation is the result of an optical torque, enhanced by the presence of the dye, which for a chiral nematic liquid crystal results in a dilation of the helical pitch.

We have studied the optical and electro‐optical properties of three different bimesogenic siloxane materials. The dimers are symmetrical and the two mesogenic groups are connected by a siloxane unit containing three Si atoms and methylene spacers. The mesogens contain F, Cl and Br substituents, respectively, laterally attached to the phenyl ring lying closest to the chiral centre of the mesogen. These materials each exhibited a broad temperature range antiferroelectric phase and large molecular tilt, which is almost temperature‐independent. We have shown that, at low temperatures, the molecular tilt in the antiferroelectric phase is the same as the apparent molecular tilt in the field‐induced ferroelectric state and is close to 45°. It was found that the antiferroelectric phase of these compounds, aligned in such way that the dimeric molecules were lying in a plane parallel to the confining substrates, exhibited very low in‐plane birefringence. For this reason, samples of the compounds inserted between cr...

A newly synthesized low molar mass liquid crystal having a flexible mesogenic group attached to methylene siloxane exhibiting smectic A phase has been used as a host for 2% (wt./wt.) dichroic dyes. The electro-optic properties of these guest–host mixtures have been studied as a function of temperature, frequency and the applied voltage. At low frequency (≲1 Hz), turbulent scattering texture was induced influenced by conduction mechanism. This texture was transformed to a clear homeotropic state due to dielectric reorientation of the smectic molecules at high frequency (>2 kHz). These materials have shown storage effects similar to monomeric and polymer smectogens. The effects of dichroic dyes on the electro-optic performances have been discussed. These systems are expected to prove functional materials for electronic displays.

Recently we have shown that short pitch chiral nematogenic bimesogens may be synthesized that couple weakly via the bulk dielectric anisotropy, but extremely strongly via the flexoelectric effect t...

This report is focus on the development of liquid crystal (LC) vis ible - light scattering devices for random lasers. These light - scattering devices are based upon binary mixtures that consist of an organosiloxane smectic A LC and a wide temperature range nematogen LC. Both the temperature range of the smectic A phase and t he dielectric anisotropy of the binary mixture are increased compared with that of the neat organosiloxane compound. In the latter case, the increase in the dielectric anisotropy results in a reduction of the magnitude of the electric field required to ind uce a clear state. Furthermore, it is found that the electric field threshold continues to decrease with increasing concentration of the nematic compound. For the random laser devices, the pyrromethene 597 laser dye was added to a mixture that was optimize d for scattering and it was found that the absorption properties of the dye becomes unstable in the presence of the electro - hydrodynamic instabilities that are required to generate scattering in the LC cells. This is believed to be due to electro - chemical reactions that occur at the electrodes. To avoid dye degradation and ensure repeatable electro - optic behaviour, a reduction - oxidation (redox) couple is dispersed within the dye - doped binary mixture. It is shown that the addition of redox dopants helps to s tabilize the dye in the scattering mixtures, and also increases the long - term repeatability of the scattering behaviour. Finally, we conclude by characterizing the random laser emission of the dye - doped binary mixture and demonstrate improved stability.

In this work we report the characterization of two organosiloxane liquid crystalline compounds by means of DSC, polarizing optical microscopy and X-ray diffraction. These compounds can be used for dye guest-host ferroelectric displays. We focus this investigation on the molecular organization of the SmC phases of the two pure compounds to help elucidate the physical behaviour of mixtures with different concentrations of the dye and the guest host. The existence of longitudinal and transverse dipoles in the molecules of the dye and the chiral guest-host respectively are responsible for the different molecular organizations in the SmC mesophases of each compound. Taking into account the experimental results and the complexity of the molecules, we present coherent models to explain the molecular arrangements in the mesophases of both compounds.

A novel mixture of low molar mass organosiloxane liquid crystals, with an optimum tilt angle of 22.5°, exhibits very good alignment. A liquid crystal binary intensity switch with a high, >; 60 dB, extinction ratio and an analogue response attenuator, with 54 dB of attenuation, suitable for telecommunication applications at λ = 1550 nm were constructed based on such a mixture. The switch and attenuator operate with fast rise times of ~ 10 μs and ~ 3.8 μs, respectively, at moderate electric fields of up to ±15 V μm-1.

This article has no abstract. Keywords: liquid crystals; magnetic fields; dielectric coupling; grid texture; permeation effect; focal conic texture; electric fields; chiral nematics; flexoelectric coupling

The flexoelectric behaviour of a hypertwisted chiral nematic bimesogenic liquid crystal is presented. Through detailed electro-optic measurements, with particular emphasis on the switching properties, we demonstrate remarkably high optical axis tilt angles. The material studied possessed a room temperature nematic phase and aligned easily on cooling under the application of a moderate electric field. Switching times of the order of 500 μs and contrast ratios of 90:1 are readily achieved. The tilt angles, measured using the rotating analyser technique, were found to be practically temperature independent and linear with the applied field. Tilt angles of 22.5° were obtained with moderate applied fields of 9.4 V/μm whilst fields of 25 V/μ yielded tilt angles of 45°. We believe these are the highest tilt angles ever recorded for such fields.

In order to develop materials that exhibit enhanced flexoelectric switching in the chiral nematic phase we have identified mesogenic units that display inherently strong flexoelectric coupling capabilities. Here we examine the oxycyanobiphenyl (OCB) moiety: homologues from the nOCB series exhibit significant electro-optic switching effects when doped with a highly chiral additive. Here we have examined lower dielectric anisotropy materials, since they allow the flexoelectric response to be extended to high field amplitudes. We show that dielectric coupling strength can be low in symmetric bimesogenic molecules. The flexoelectric response of such a molecular structure is tested by doping a homologue from the series CBOnOCB with a chiral additive: very significantly we find that the optic axis is rotated through 2φ = 45° in 90° at E =...

The effect of a photoisomerising dye in a ferroelectric liquid crystal host has been investigated. A nitroazo dye incorporating the same three-siloxane unit as an organosiloxane ferroelectric host has been used to insure good miscibility and high dye concentrations. The effect of photoisomerisation by 300-400 nm UV of up to 430 mW.cm -2 has been investigated in two mixtures with 25% and 50% molar weight of dye. The 25% mixture has an I-SmC * -crystal phase sequence, while the 50% mixture has I-SmA * -SmC * -crystal. Transition temperatures of both the mixtures are reduced by increased UV illumination. For the first mixture at a constant temperature, the spontaneous polarisation in the ferroelectric phase is reduced by UV illumination. For the second mixture both the spontaneous polarisation and tilt angle of the SmC * phase are reduced by UV illumination and the phase is changed from SmC * to SmA * at temperatures close to the transition. The change of tilt angle and observations of micrograph textures indicate that this is a macroscopic change of the material rather than any phase separation of the dye and host materials.

The photoisomerisation of a flexoelectric chiral nematic bimesogen system dyed with an azo dye has been investigated. The host material has a pitch and field dependent tilt angle that are temperature independent. Upon illumination by ultra violet, the azo dye molecules undergo a shape change from their trans to cis isomer. The effect of the shape change of the dye on the mixture is to decrease the I-N* transition temperatures, to increase the response times and to decrease the transmitted optical intensity. For the same reduced temperatures, the tilt angles, pitch and threshold voltages for the transition from focal conic to homeotropic textures are unchanged. The macroscopic parameters observed suggest that the orientational order parameter of the system is reduced by UV illumination. The cis isomers do not appear to separate from the host material or significantly change the flexoelectric coefficient.

We present a study on a series of dye guest-host mixtures using fluorescent perylene-based molecules as the guest dye in an organosiloxane host. These hosts have temperature-independent switching, at room temperature, through 90° for fields of the order of 10 Vrms/μm. Perylene molecules have been grafted onto the organosiloxane moiety via an alkyl spacer producing novel and rugged fluorescent dyes that are readily miscible in the host. Micro-separation of the low molar mass siloxane groups in the mesophases tend to form smectic phases. These planes produce an effective two-dimensional polymer backbonethat engenders the rugged mechanical properties of polymeric liquid crystals onto these low molar mass ferroelectric liquid crystals. In this study we show how the introduction of the dye molecules affects the electro-optic properties of the organosiloxane host.

In a chiral nematic liquid crystal, the flexoelectric effect consists of a fast and linear coupling with an applied electric field. One difficulty to overcome is the unwinding of the helix that occurs at higher fields due to dielectric coupling. The use of bimesogens, which possess very low molecular dielectric anisotropy can improve flexoelectric characteristics. New bimesogen compounds have recently been synthesised that exhibit switching angles of 45° for applied fields of about 9 V.μm−1. In this paper, results from dielectric, electro-optic and dynamic light scattering measurements are reported for the new bimesogenic mixture. The dielectric anisotropy Δe changes sign with temperature and its values range between -0.2 and 0.3 for the temperature range studied. For Δe weakly positive, no electric field Freedericksz transition could be induced but Williams domains are observed instead. The large decrease in the bend elastic constant to viscosity coefficient ratio is attributed to a large increa...

In this paper we present the results of mixing fluorinated and non-fluorinated organosiloxane materials based on ferroelectric and antiferroelectric low molar mass organosiloxane (LMMO) liquid crystals. None of the fluorinated materials exhibit a mesophase, however when mixed with the non-fluorinated analogues a ferroelectric phase is observed. We present the resultant phase diagrams together with the spontaneous polarisation curves of the mixtures.

The twist elastic constant, K-2, and the rotational viscosity coefficient, gamma (1), are of importance when the response time for the in-plane switching mode is studied. Since adding dopants is one technique to improve the response characteristics, the effect of dopants on these physical properties is significant. The effect on K-2, and gamma (1) of adding alkyl(alkoxy) phenylcyclopentenones and alkyl(alkoxy) cyanobiphenyls to the base mixture ZLI-4792 together with their temperature dependence have been investigated using different temperature scales. The reduced temperature scale showed the effect of these dopants on K-2 is small. On the other hand, the temperature dependence of gamma (1) depends on both the absolute temperature scale and the reduced temperature scale. Therefore, it is clear that the choice of temperature scale with which to compare gamma (1) for different systems raises fundamental questions which way not have a unique answer.

We present a modified version of a Raman microspectroscope designed for dynamical studies of thin liquid-crystalline films in glass cells. This system is based on a confocal geometry and a multi-channel liquid nitrogen cooled CCD detector. The confocal arrangement makes possible the study of volumes only a few μm3 in size within a liquid-crystal cell with an axial resolution of 14 μm. The multi-channel detector allows high quality spectra to be recorded in a few seconds with less than 10 mW of laser power at the sample. Using an electrooptic modulator, dynamic studies can be done on a microsecond time scale. We present results obtained during the electrical switching of a anti-ferroelectric liquid-crystalline low molar mass organosiloxane material.

In this paper we present the synthesis and physical characteristics of novel fluorinated organosiloxane materials based on ferroelectric and antiferroelectric low molar mass organosiloxane (LMMO) liquid crystals. AH the fluorinated materials are isotropic at room temperature, however we have prepared mixtures with the analogous non-fluorinated organosiloxanes. We present the resultant phase diagram together with the spontaneous polarisations of the mixtures.

In this paper we show the effect of addition of monomeric and bimeric azo and stilbene organosiloxane dyes to ferroelectric liquid crystal (FLC) devices. These dyes show SmA phases, which are miscible at all concentrations, in our benzoate host. Simple mixing of host liquid crystal and dye allow us to control the spontaneous polarisation, tilt angle or phase range. This allows applications from birefringent devices to single polariser dye guest host devices. The SmA* phases induced show marked electroclinic effects. The effect of dye addition favourably alters the phase sequence allowing easier alignment and room temperature ferroelectricity. The bi-azo dye produced an antiferroelectic phase, which we attribute to a templating effect.

In this paper, we will show how, using organosiloxane liquid crystals with the same chiral mesogen, we can generate (through a template effect) ferroelectric or antiferroelectric phases simply by controlling the length of the siloxy group. By partially fluorinating the aromatic rings or perfluorinating the terminal chains we generate extremely high spontaneous polarisation materials with very broad temperature ranges. By controlling the cross-section of the mesogen in relation to that of the organosiloxane moiety we can select the tilt angle at will. Materials have been synthesised and studied that exhibit tilt angles of 45° in the antiferroelectric phase over 60°C wide temperature ranges and this makes them ideal for many AF device applications. Response times of 10 to 100μs were recorded in moderate fields (≤ 10V/μm) and for Ps ∼ 10–100 nC/cm2 and the materials gave excellent bi- or tri-stability. This molecular control of the bulk electro-optic properties leads to a new range of materials suitable for both birefringence and dye guest host devices. We have applied these principles to a number of asymmetric organosiloxane liquid crystals in which the dichroic and fluorescent dye moieties form part of the mesogen and give extremely high solubility. By using these materials we have been able to generate both bistable digital and analogue devices with switching properties independent of temperature over a wide temperature range.

In this paper we present a modified ‘rotating analyser’ technique that allows rapid and continuous in situ measurements of the optical tilt angle (θ). Using this technique we will detail the tilt angle behaviour in mono-mesogen (AB) and bi-mesogen (ABA) low molar mass orga- nosiloxanes. The AB type molecules exhibit only the ferroelectric SmC* phase and possess a high tilt angle (42-45°) that is independent of temperature throughout the phase range. The ABA molecules containing three silicon atoms exhibit antiferroelectric SmC*Aphases. The tilt angle behaviour during a field induced SmC*A- SmC* transition has also been investigated.

The physical characteristics of a new fluorinated organosiloxane material are presented, and compared to those of its non-fluorinated homologue. The fluorinated material has a high Ps (200–450 nC/cm2) and a high tilt angle (∼38°) over a 100°C wide temperature range. Both materials exhibit antiferroelectric phases. As the fluorinated material is cooled, its behaviour becomes more ferroelectric-like. We discuss this behaviour in relation to the molecular structure of the materials.

A multi-layered device has been produced with a similar operating mode to a polymer dispersed liquid crystal (PDLC), but with a low molar mass (LMM) nematic mixture sandwiched between two homeotrop...

A new Raman microspectroscope was designed for the study of thin liquid-crystalline films in glass cells. This system is based on a confocal geometry and a multi-channel liquid nitrogen cooled CCD detector. The confocal arrangement makes possible the study of volumes only a few μm3 in size within a liquid-crystal cell with an axial resolution of 7 μm. The mutli-channel detector allows high quality spectra to be recorded in less than a second with only a few milliwatts of laser power at the sample. Using an electro-optic modulator, dynamic studies can be done on the millisecond scale or smaller. We present the first results obtained with this technique of the electrical switching of a ferroelectric liquid-crystalline low molar mass organosiloxane material.

We present a new type of ferro- and antiferroelectric liquid crystal, based on bimesogenic systems with a siloxane spacer as the linking unit. Liquid crystalline materials bearing a perfluorinated chiral lactic acid ester as the terminal chain, were synthesised. We present the mesomorphic properties of these materials and discuss the influence of the siloxane linkage and the fluorine content on the phase behaviour.

A series of chiral bimesogenic compounds has been synthesized. The molecules comprise beta-estradiol as the central chiral unit, which is attached to a terminal 4'-cyanobiphenyl-4-yl group at C-17 by an alkanoate spacer containing 5, 6 or 11 carbon atoms. At C-3 the estradiol moiety is substituted with an omega-alkenyloxy chain, also containing 5, 6 or 11 carbon atoms. We will describe the synthesis and phase characterization of these materials. The compounds with 5 or 11 carbon atoms in the spacer separating the mesogens display chiral nematic mesophases with temperature ranges up to 40 ° C, entering the isotropic state at about 100 ° C. The pitch lengths of these pure materials are remarkably invariant with temperature. Their electro-optic behaviour has been characterized, with particular emphasis on their flexoelectric properties. The materials have the highest flexoelectric coefficients reported so far in any chiral nematic liquid crystal [with e (kappa-1) < + 0.5 C N -1 m -1], with flexoelectro-optic...

We have established that the antiferroelectric order observed in low molar mass organosiloxane liquid crystal materials with chiral bi-mesogen molecules is due to the bent conformation of the molecules rather than to co-operative antiferroelectric interactions. The switching between antiferroelectric and ferroelectric order involves a change of conformation of the molecules. We show that in mixtures of antiferroelectric and ferroelectric molecules this concept can be used to vary continuously the threshold field for antiferroelectric switching. We propose a simple model to describe the behaviour of the materials and to predict the threshold field.

In low molar mass organosiloxane liquid-crystal materials the siloxane moieties micro-separate and aggregate in planes that could be regarded as an effective or virtual two-dimensional polymer backbone. We show that if a siloxane moiety is attached to a dichroic dye molecule, the micro-segregation of the siloxane moieties makes it possible to include a high concentration of the guest dye (more than 50%) in a host organosiloxane solution. This effect, combined with the temperature independent tilt angles achievable with ferroelectric organosiloxane liquid crystals, provide an ideal material for high-contrast surface-stabilised ferroelectric display devices. We present dyed ferroelectric materials with a temperature independent tilt angle greater than 42 degrees, a wide (room temperature to over 100[ddot]C) mesomorphic temperature range and a response time shorter than 500μs in the dye guest host mode.

We present a new shear aligned polymer dispersed ferroelectric liquid crystal material which in this configuration possesses the same electro-optical characteristics as conventional surface stabilized ferroelectric liquid crystals. The sample thickness is 20mum as opposed to the 1-2mum used in the normal surface stabilized geometry. The new material shows switching on the 100mus timescale and very high bistability (G>0.8) minutes after removal of the field. The temperature independent apparent tilt angle is 25 at room temperature, almost equal to the ideal value of 22.5 for many display applications. The material is prepared from a solution of a novel low molar mass organosiloxane ferroelectric liquid crystal in a UV-curable polymer. We study the physical properties of the composite material and give a description of the fabrication technique and its optimization. The material and fabrication technique could be readily used for industrial production of devices including flexible display panels.

On the basis of DSC calorimetry and thermo-optic (TOA) measurements the mesomorphic properties of the strongly polar Schiff bases family, 4-chlorobenzylidene-4′-alkylanilines (CBnA), are presented. Two kinds of mesophases were found: smectic A and smectic B. For the first time detailed calorimetric properties of the investigated family are presented and discussed. Very narrow smectic A phase for the nonyl, decyl, undecyl and dodecyl derivatives was detected. Smectic mesophases in butyl, pentyl and dodecyl derivatives are monotropic. These results are compared with our earlier results [1].

In this paper we describe a novel transreflective display construction that provides excellent visibility in all ambient lighting conditions, from dark to full sunlight. The technology uses a combination of liquid crystal and electroluminescent elements, is capable of low cost fabrication on a single flexible substrate, and is powered using a single electronic drive circuit.