Adsorption processes during the filling of a display with a smectic A LC mixture

The separation of a smectic A liquid crystal (LC) mixture during the filling of a large area display was studied. This process is governed by the selective adsorption of the mixture's ionic dopant on the surface of the display substrates, leading to a non-uniform distribution of the dopant in the LC over the display area and resulting in defective regions. Conductivity measurements were performed to indicate the distribution of the dopant concentration in the LC over the display area. The consequences of mixture separation on the structure of the LC and on the display's electro-optical properties are discussed. Factors to reduce the extent of separation of the mixture are revealed using a general theory of chromatography. Increasing the cell gap, decreasing the area of the glass surface by reducting the gap between the ITO electrodes, and increasing the back pressure during filling, effectively reduce the significance of the separation process. The results obtained can be used when designing and filling displays based on the electrically reversible memory effect in a smectic A LC or displays based on dynamic light scattering in a nematic LC.     

Hydrogen bond network-stabilisation of blue phases by addition of a chiral N-(10-hydroxydecyl)succinimide derivative and alkane diols

Blue phases (BPs) obtained by doping a commercially available liquid crystalline compound (4-butyl-N-(4-ethoxybenzylidene)aniline (EBBA)) with (2R,3R)-2,3-bis(4-octyloxyphenylbenzoyloxy)-N-(hydroxydecyl)succinimide (1) were highly stabilised by the addition of a small amount of alkane diols. Especially, addition of only 0.5 mol% of octane-1,8-diol increased the BP–Iso transition temperature by 10 K and widened the BP temperature range up to 35 K. A model stabilisation mechanism based on the construction of a hydrogen bond network in each disclination zone in BPs was proposed.     

Design of advanced multicomponent ferroelectric liquid crystalline mixtures with submicrometre helical pitch

New functional multicomponent ferroelectric liquid crystalline mixtures have been designed while searching smart self-assembling materials with submicrometre periodicity of the helical structure responding definite demands for application in electro-optic devices and photonics that exploit the deformed helix ferroelectric effect. The resulting designed mixtures possess the paraelectric smectic A* and the tilted ferroelectric smectic C* phases over a very broad temperature range down below the room temperature. The mesomorphic, electro-optic and dielectric properties have been studied and discussed. The presence of a very stable enantiotropic ferroelectric smectic phase exhibiting almost temperature independent helical pitch within 150–250 nm range and reasonably high values of the tilt angle might allow these mixtures to be applicable for practical purposes.     

Mesomorphic phase transitions and electro-optical properties of benzyl fluoroalkyl thioether liquid crystalline compounds

Four series of liquid crystalline (LC) compounds containing benzyl perfluoroalkyl thioether groups (BFT), 4-n-alkoxyphenylbenzyl perfluoroalkyl thioethers (nO-BBFT-FmF), 4-n-alkoxyphenylbenzyl perfluoroisoalkyl thioethers (nO-BBFT-FmIF), 4-n-propylcyclohexylbenzyl perfluoroalkyl thioethers (3-C1BFT-FmF) and 4-ethylcyclohexyl-3'-fluorobenzyl perfluoroalkyl thioethers (2-C1FBFT-FmF), were synthesized and their mesomorphic phase transitions and electro-optical properties investigated. nO-BBFT-FmF and nO-BBFT-FmIF have SmA, SmB and CrE phases, while 3-C1BFT-FmF and 2-C1FBFT-FmF showed a SmB phase. It was found that the appearance of a LC phase and the thermal stability were closely connected with the chemical structures of the rigid core part and the terminal groups. The electrooptical properties were investigated for BFT using ZLI-1132 as nematic solvent. Some of the BFT compounds have a good solubility of 15 wt % in ZLI-1132 and can be used as a component for lowering the refractive anisotropy (Delta n) of the host ZLI-1132 solvent.     

Polarization holographic grating recording in the cholesteric azobenzene‐containing films with the phototunable helix pitch

The recording of polarization gratings in films of a cholesteric liquid crystalline polymer with different helix pitch was studied in detail. For this purpose, the cholesteric mixture of the nematic azobenzene‐containing copolymer with a chiral‐photochromic dopant was prepared. The utilization of such mixture has made possible to realize dual optical photorecording in one system, first due to the phototuning of the helix pitch by UV light and second the polarization grating recording process by exposure with polarized visible light. The diffraction efficiency strongly depends on the cholesteric helix pitch and films thickness: the increase of the confinement ratio d/p (where d, film thickness; p, helix pitch) results in growth of the diffraction efficiency. Comparison of the induction of polarization gratings in cholesteric, nematic (copolymer without chiral dopant), and amorphous (nonannealed) cholesteric films revealed that only the cholesteric films were characterized by significant oscillations in the diffraction efficiency signal as well as by the presence of the maximum in the first‐order diffraction efficiency in the initial stage of the grating recording process. It was found that in addition to the polarization grating surface relief gratings (SRGs) were also formed in the studied systems, however, the amplitude of the SRG inscribed in the cholesteric films was lower (～20 nm) compared to the grating amplitude obtained in nematic films (～60 nm). Moreover, increasing helix pitch resulted in a decrease of the SRG amplitude. The obtained experimental data demonstrate the great potential of cholesteric LC mixtures of such type for different applications as photoactive materials for photonics. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 773–781     

Synthesis of a series of novel chiral smectic C (Sc*) phase shish‐kebab type liquid crystalline polymers

A series of chiral smectic C phase shish‐kebab type liquid crystal polymers was synthesized by low‐temperature solution condensation polymerization from 2,5‐bis[4‐((S)‐alkoxyl)benzoyloxy]hydroquinone and aliphatic diacylchloride. The monomers and their precursors were identified by using elemental analysis, infrared spectrum, nuclear magnetic resonance and mass spectrometry. The polymers were characterized by gel permeation chromatography, differential scanning calorimetry, thermogravimetric analysis, temperature‐variable X‐ray diffraction, polarimeter and polarizing microscope (POM) with a heating stage. All the polymers entered into liquid crystal phase when heated to above their melting temperature. The Schlieren texture and sanded texture were observed on POM. All the chiral compounds and polymers showed high optical activity. Temperature‐variable, X‐ray diffraction study together with the POM and polarimetric analysis revealed that the polymers synthesized are chiral smectic C phase. Thus, the present report provides examples of shish‐kebab type polymers that form a chiral smectic C phase. The change of the melting temperature and isotropization temperature with the variation in molecular structure was also discussed. Copyright © 2000 John Wiley & Sons, Ltd.     

Phase modulation using different orientations of a chiral nematic in liquid crystal over silicon devices

Modulation of the intensity of light by high quality reflective micro-displays is predominantly carried out by liquid crystal over silicon (LCoS) spatial light modulator (SLM) technology for applications such as pico-projectors. Wider use of these devices, in applications such as computer-generated holography and optical correlation, is limited by their phase modulation ability and illumination polarisation state dependence. These devices rely on planar or twisted nematic liquid crystals to modulate the light, but due to their viscoelastic properties they are inherently slow. Research into the use of the polymer stabilised blue phase has already shown that it can offer high speed phase modulation. However, other chiral nematic orientations are yet to be compared in LCoS devices. In this article, we demonstrate that polymer-stabilised chiral nematic liquid crystal electro-optical effects can offer phase modulation in silicon backplane devices. The uniform standing helix and focal conic textures are shown to be independent of the input light polarisation state and the uniform lying helix is shown to be polarisation dependent. These optical responses are then compared with that of the blue phase to identify a suitable orientation for further development in LCoS technology in order to find a high-speed, full phase modulating material.     

Doping effects of fluorinated chiral dopant in blue phase liquid crystals and its electro-optical behavior

ABSTRACT

We reported a fluorine-containing binaphthyl derivative, denoted as BD-F, which showed a low helical twisted power. The blue phase liquid crystal (BPLC) doped with BD-F achieved a lower operating voltage than that only used traditional chiral dopant, resulting from the larger dielectric property of fluorinated BD-F. In addition, the BPLC composite exhibited a wider temperature range and an enhanced Kerr effect with the decreased frequency. In terms of the applications, the devices revealed microsecond response time, thereby providing broad prospects for photonics and displays.     

Photoinduced phase transitions and helix untwisting in the SmC* phase of a novel cinnamoyl-based liquid crystal

A photoinduced phase transition and helix untwisting in a new liquid crystal forming the SmC* phase were studied in detail. The compound consists of a cinnamoyl photosensitive fragment with C?=?C double bond capable of photoisomerisation and photocycloaddition. It was shown that ultraviolet (UV) irradiation (365 nm) induces an extreme decrease in phase transitions temperatures (SmC*–SmA*, SmA*–N*, N*–I). Vertically aligned samples in the SmC* phase cause selective light reflection in the visible spectral range. The light action results in a noticeable helix untwisting that causes a shift in the selective light reflection peak to the long-wavelength spectral region. The temperature dependence of spontaneous polarisation P _s was measured and it was found that UV irradiation induces a decrease in the values of P _s. Photo-optical phenomena taking place in the liquid crystal are attributed to the formation of photoproducts having low anisometry, which disrupts mesophases.     

The temperature and concentration dependence of helical pitch in the mixtures of antiferroelectric compounds with the opposite helical twist sense

The temperature dependence of helical pitch for members of an homologous series of orthoconic antiferroelectric compounds (3FmHPhF) and their bicomponent mixtures (m = 3 and 5 as well as m = 3 and 7) has been measured by the method of selective light reflection. The compounds have the same chiral centre but they have different temperature dependence of the helical pitch as well as the helical twisting sense in SmC*_A phase: right for member m = 3, left for m = 7, and both right and left for m = 5. For this last homologue, the change of twisting sense is connected with the appearance of the unwound structure. Concentration dependence on helical pitch was investigated in the mixtures. It was demonstrated that it is possible to obtain mixtures with desirable high pitch and also with totally unwound structure.     

On the thickness dependence of ferroelectric polarization in smectic C* liquid crystal cells

The thickness dependence of ferroelectric polarization in a SmC* liquid crystal exhibiting a large value of polarization has been investigated. It is observed that the saturation value of the polarization shows no significant thickness dependence. This observation is in accordance with a recent theoretical framework developed by Galerne. It is shown that the wall thickness, where the polarization undergoes a reversal, and hence the self-screening effect, is insignificant in the material studied.     

Synthesis and characterization of novel ferroelectric liquid crystal polysiloxane containing undecanoyloxy spacer (I)

A novel side-chain liquid crystal polysiloxane and its corresponding monomer were synthesized by the standard method. We ensured their structures were as expected and their purities were high by ¹H nuclear magnetic resonance and infrared measurements. They were studied by differential scanning calorimetry (DSC) for their thermal analysis and polarizing optical microscopy (POM) with hot stage for their textures and transition temperatures. The results showed good liquid crystal properties and low transition temperatures of the mesophase. X-ray diffractions were done to research their layer structure and SmA and SmC^* phases were assured, in good agreement with the results of the POM and DSC measurements. The optical rotation degree was also measured.     

Dielectric relaxation spectroscopy and electro-optical studies of phase behaviour of a chiral smectic liquid crystal

Dielectric relaxation processes in various phases of a chiral smectic liquid crystal compound have been investigated over a wide range of frequencies from 10 to 300 kHz. Dielectric spectroscopy reveals the existence of two relaxation frequencies corresponding to the ferroelectric and ferrielectric Goldstone modes in the range of temperature where two different phases coexist. This phenomenon of coexistence is examined with respect to the cell thickness and reversal temperature.     

Broadband reflection characteristic of polymer-stabilised cholesteric liquid crystal with pitch gradient induced by a hydrogen bond

A polymer-stabilised cholesteric liquid crystal (PSChLC) was fabricated by ultraviolet (UV) induced polymerisation of photopolymerisable acrylate monomers mixed in a cholesteric liquid crystal (ChLC). A polymer network with a concentration gradient, which was induced by UV light absorption of dye along the propagation direction, was formed. A hydrogen bond, arising between the polymer network with a concentration gradient containing carboxyl as proton donors and chiral dopant (CD) as proton acceptors, induced a pitch gradient in PSChLC and then, as a consequence, broadband reflection. The broadband reflection is associated with the concentration and the composition of photopolymerisable acrylate monomers, the concentration of CD and the polymerisation temperature. Examining the morphologies of the polymer network by scanning electron microscopy, the helix structure and pitch gradient were verified, confirming the pitch gradient of the PSChLC and revealing the essence of the formation of broadband reflection.     

CdSe quantum dots in chiral smectic C matrix: experimental evidence of smectic layer distortion by small and wide angle X-ray scattering and subsequent effect on electro-optical parameters

CdSe quantum dots (QDs) dispersed ferroelectric liquid crystal (FLC) has been subjected to small and wide-angle X-ray scattering and atomic force microscopy to understand the molecular organization in chiral smectic C (SmC*) phase. SAXS indicates that the presence of QDs causes enhancement in the smectic layer separation. The smectic order parameter for neat FLC and FLC–QDs mixtures is obtained in the range of 0.6 to 0.85. Both smectic order parameter and structural tilt are found to be lesser for FLC–QDs mixtures as compared to neat FLC. The insertion of QDs in SmC* matrix causes localized smectic layer distortion in such a way that spontaneous polarization remains almost the same but the electro-optic switching of molecules becomes faster. We have outlined the superiority of FLC–QDs mixtures for electrical energy storage and their suitability in electronic devices.     

单硫代和双硫代甘油醚在直链淀粉-三（3,5-二甲基苯基氨基甲酸酯）固定相上的手性拆分

合成了直链淀粉三(3,5二甲基苯基氨基甲酸酯)手性固定相。用该固定相对6种单硫代甘油醚和4种双硫代甘油醚进行了手性拆分。单硫代甘油醚对映异构体得到了较好的分离,而双硫代甘油醚完全不能拆分。提出了样品与固定相的作用模式。