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A new pentaphenyl liquid crystalline (LC) compounds with 2,3-difluorobenzene moiety exhibiting wide nematic range have been prepared. The key stage is the condensation of the corresponding 3-dimethylaminopropanoyl-4-pentyl benzene hydrochloride with substituted methyl benzyl ketone in the presence of base leading to 3,6-disubstituted cyclohexenones. Methylation with methyl magnesium iodide followed by oxidative aromatization gives three-ring bromides, which are used in the Suzuki cross-coupling reaction. Pentaphenyl LC compounds possessing lateral methyl group have moderate melting points, improved solubility, and miscibility with another LC components. The new compounds could be useful in LC compositions with the high optical anisotropy. [ABSTRACT FROM AUTHOR]

The aim of this present paper is to compare the effects of conducting polymer, poly (3,4-ethylenedioxythiophene) nanotubes and carbon nanotubes, on the electro-optical properties of a nematic liquid crystal mixture (1770-2). From the optical transmission and capacitance behavior it has been proved that the conducting polymer - nematic liquid crystal system possesses much lower threshold voltage and driving voltage than the carbon nanotube - nematic liquid crystal system which might be very useful in display applications. The effective elastic constant has been also significantly reduced in the conducting polymer - nematic liquid crystal system. [ABSTRACT FROM AUTHOR]

We have studied a compound (S)-(+)-4-(1-methylheptyl) 4-[4-(3-hexanoyloxyprop-1-oxy)benzoyloxy]biphenylate by means of differential scanning calorimeter, polarizing microscope and dielectric spectroscopy. This compound shows exceptionally a wide temperature range of [image omitted] phase ∼9°C together with a paraelectric SmA* phase. A relaxation mechanism in the high kHz region has been detected for the [image omitted] phase under planar orientation of the molecules. This mechanism has been characterized with temperature and bias electric field. Recent theoretical advances predict two different nature of dielectric relaxation mode in the [image omitted] phase (Phys. Rev. E, 69, 031709, 2004). Our experimental results confirm two different behaviors of this relaxation mode in different temperature range of the phase. [ABSTRACT FROM AUTHOR]

In this paper a tunable broad-band polarizer based on the photonic crystal fiber (PCF) filled with liquid crystal (LC) is presented. Host PCF is made of glass with 1.518 refractive index and ordinary refractive index of the LCs is lower than glass index. Numerical simulations have proven that by changing LC orientation from planar to transverse a broad-band single-polarization guidance is possible: for planar orientation of LC molecules both polarizations are index-guided, whereas for transverse orientation only one polarization is index-guided. Also some initial experimental results are included showing that polarization dependent losses and phase birefringence can be tuned with transverse electric field. [ABSTRACT FROM AUTHOR]

Switching and dielectric relaxation phenomena were investigated for an antiferroelectric liquid crystal, 4,4-(1-methyloctyloxycarbonyl)phenyl]-4'-[3-(butanoyloxy)prop-1-oxy]biphenyl carboxylate, exhibiting chiral smectic A (SmA*), smectic C (SmC*) and antiferroelectric (SmCA*) phases. Spontaneous polarisations, rotational viscosities, relaxation frequencies, dielectric strengths and distribution parameters were determined as a function of temperature. The electric field required for saturation of the spontaneous polarisation increased with a decrease in temperature. In the SmA* phase, only one relaxation mechanism was observed that behaves as soft mode. Two relaxation processes were detected in the SmC* phase. A high-frequency relaxation process invariant at 2.2 kHz was due to a Goldstone mode, but the origin of low-frequency relaxation process (1-20 Hz) is unclear; however, it may belong to an X-mode. The dielectric spectrum of the SmCA* phase exhibits two absorption peaks separated by two decades of frequency. The low-frequency peak is related to the antiferroelectric Goldstone mode, whereas the high-frequency peak originates from the anti-phase fluctuation of the directors in the anti-tilt pairs of the SmCA* phase. [ABSTRACT FROM AUTHOR]

We have designed, synthesized, and evaluated the physical properties of some high birefringence (Δn) isothiocyanato phenyl-tolane liquid crystals. These compounds exhibit a Δn ≃ 0.48-0.52 at room temperature and wavelength λ = 633 nm. Laterally substituted short alkyl chains and fluorine atom both eliminate smectic phase formation and lower the melting temperature. Both the moderate melting temperature and very high clearing temperature make those compounds attractive for eutectic mixture formulation. Examples of the mixtures containing the described components are presented. [ABSTRACT FROM AUTHOR]

High birefringence (Δn > 0.4) nematic liquid crystals are particularly attractive for infrared applications because they enable a thinner cell gap to be used for achieving fast response time. In this paper, we report the mesomorphic and physical properties of several fluorinated NCS terphenyl single compounds and mixtures based solely on laterally fluorinated aromatic rigid core structures. The single compounds have Δn ∼ 0.35 in the visible spectral region and relatively low viscosity. In terms of applications, these compounds can be used as a dopant for enhancing the figure-of-merit of commercial mixtures for display applications. Or we can formulate high birefringence eutectic mixtures using solely NCS terphenyl compounds for near IR laser beam steering applications. [ABSTRACT FROM AUTHOR]

We have designed, synthesised and evaluated the physical properties of high-birefringence (Δn) isothiocyanato phenyl-tolane and terphenyl liquid crystals. These compounds exhibit a Δn∼0.36-0.52 at room temperature and wavelength λ = 633 nm. A different mesomorphic sequence was observed depending on the terminal alkyl chain length. Compounds with a longer chain show smectic and nematic phases, whereas short-chain homologues only exhibit a nematic phase. In the vicinity of the nematic-to-smectic transition, the viscoelastic coefficient decreases, instead of increases, as the temperature decreases. The observed change is as large as 75% for the 4'-(3,5-difluoro-4-isothiocyanatophenylethynyl)-4-pentylbiphenyl compound studied. This behaviour is useful for improving the response time of a liquid crystal device, if the operating temperature can be controlled accurately. [ABSTRACT FROM AUTHOR]

The homologous series of mesogenic (S)-4''[n-(perfluoroalkanoyloxy)hexyl-1-oxy]-4-(1-metylheptyloxy-carbonyl)terphenyl compounds exhibiting low temperature, wide range, near orthoconic antiferroelectric phase has been synthesized [1]. Compounds of the homologous series differ from each other by a position of a single fluorine atom substituted at the phenyl ring of the molecular rigid core. This affects the mesogenic behavior. Moreover, the molecular dipole moment of the compound as well as the physical parameters of the antiferroelectric phase are changed. The importance of the molecular dipole moment orientation and magnitude for the mesogenic behavior and physical parameters of the orthoconic antiferroelectric phase is discussed. [ABSTRACT FROM AUTHOR]

High birefringence (Δn>0.4) nematic liquid crystals are particularly attractive for infrared applications because they enable a thinner cell gap to be used for achieving a fast response time. In this experiment, we evaluate the mesomorphic and physical properties of several fluorinated NCS terphenyl compounds. These compounds have Δn∼0.35 in the visible spectral region and relatively low viscosity. In terms of applications, these compounds can be used as a dopant to enhance the figure-of-merit of commercial mixtures for display applications. We can also formulate high birefringence eutectic mixtures using solely NCS terphenyl compounds for near-IR laser beam steering applications. [ABSTRACT FROM AUTHOR]

Abstract: By mixing a commercial broad-temperature-range nematic liquid crystal mixture with a single-component antiferroelectric chiral smectic exhibiting two different chiral smectic-C-type phases as only mesophases, we have induced three phases which appear in neither of the two components; the paraelectric SmA∗ phase and the so-called intermediate phases and , antiferroelectric and helielectric in nature, respectively. The generation of the two latter phases in mixtures where one component is an essentially non-chiral nematic is highly unexpected, since these phases are generally linked to high degree of smectic order and/or strong chiral interactions. It is probably made possible through microphase segregation driven by the incompatibility of the fluorinated tail of the smectic component with the non-fluorinated constituents of the nematic mixture. We also doped the nematic with single-wall carbon nanotubes (SWCNTs) before adding it to the smectic at the same concentration, allowing us to study the effect of SWCNTs on antiferroelectric liquid crystals. Although the final SWCNT concentration was very small (0.002wt%) the phase sequence was radically altered, the ordinary SmC∗ phase now being present all the way between SmA∗ and crystallization, while all other variations of smectic-C-type order were suppressed. [Copyright &y& Elsevier]

We have investigated the static and dynamic electrooptical effects of adding an alignment layer derived from a chiral liquid crystal having SmC* and N* phases to the standard polymer alignment layer in antiferroelectric liquid crystal cells. Our results show that the added layer reduces the relaxation time of the liquid crystal, the threshold voltage and the dynamic range required to generate a full greyscale. The electrooptical response of materials was tested using a 7 level waveform, and the relaxation was studied using a novel memory test. [ABSTRACT FROM AUTHOR]

Results of dielectric studies for three tolane derivatives containing the isothiocyanato (NCS) and alkyl or alkoxy groups in the terminal positions are presented. A relaxation process associated with molecular rotations around the short axes has been observed in the crystal-like smectic phases (B, E, K). The K phase was characterized for the first time by dielectric spectroscopy. The results are discussed by taking into account the dielectric relaxation data obtained recently for the biphenyl analogues in the E phase. The available X-ray data allow us to calculate the so-called packing parameter which characterizes the free volume of the molecules in the unit cells. [ABSTRACT FROM AUTHOR]

The use of antiferroelectric liquid crystals(AFLCs)on practical applications is often precluded by their low contrast. Orthoconic AFLCs, in principle, may overcome this limitation, for they behave as isotropic plates at normal incidence. A number of orthoconic AFLC materials have been evaluated. Multiplexed seven-level driving schemes have been employed for dynamic analysis. The most relevant results include average static contrast ratio over 200:1 and dynamic contrast ratio over 130:1. On the other hand, hysteresis often shows slight voltage shifts when the cells are driven with low frequency AC signals. This feature impairs symmetry of the transmission maxima on the positive and negative lobes of the hysteresis curve. The effect is attributed to the extremely low pitch of actual orthoconic materials–usually below 1  μm. The distinctive properties of orthoconic materials make them suitable for photonic applications requiring moderate response time such as routing or beam steering applications. [ABSTRACT FROM AUTHOR]

Polymer-dispersed liquid crystals containing orthoconic antiferroelectric smectics were prepared by photopolymerization-induced phase separation. Mean droplet size allowed formation of antiferroelectric helix inside droplets. Bias electric field applied during phase separation aligned helical axes parallel to the cell plane. Obtained ellipsoidal droplets were optically uniaxial for perpendicular light beam. The cells were switched by square or triangle driving signal unwinding the helix. V-shape switching was found instead of threshold one observed in conventional cells of the same mixture. The switching time was crucially depended on temperature. Those effects were caused by anchoring conditions inside polymer cavities. [ABSTRACT FROM AUTHOR]

Addressing waveforms for reflective LCOS devices filled with V-shape chiral smectic liquid crystals, have been tested and optimised. Analogue greyscale generation has been tested on passive devices mimicking the behaviour in active matrix based devices. A comparative study of a number of experimental chiral smectic mixtures showing V-shape response has been carried out. Specific driving waveforms have been designed and optimised in order to improve the material's electro-optic response. This procedure is lengthy since every voltage level of the waveform ought to be separately optimised, and interdependences between the different waveform fragments lead to an iterative optimisation process. The effect of a short blanking pulse named well pulse has been particularly remarkable, thus forcing a thorough tune-up as a function of working temperature and video rate. [ABSTRACT FROM AUTHOR]

In this letter, we report a new very large mode area multimode photonic band-gap (PBG) propagation in a solid core photonic crystal fiber (PCF) filled with a liquid crystal (LC). The host fiber was designed with a 50-\mum core diameter to optimize the light coupling from standard multimode fibers. After filling it with LCs, multimode selective propagation was observed and it was possible to tune the bands with temperature. The mode field was well localized in the core area and compared to our previous works, a much smaller percentage of optical power penetrates the LC-filled holes. Consequently, the scattering loss is reduced, allowing for lower insertion losses. Attenuation was measured by the cut-back technique and for one of the band gaps it was 0.16 dB/cm, which, to the best of our knowledge, has been the lowest level of attenuation reported so far in PBG-guiding LC-filled PCFs. [ABSTRACT FROM PUBLISHER]

Two methods of synthesis of chosen 1-[4-(1-methylheptyloxycarbonyl) phenyl]-2-[4'-(2,2,3,3,4,4,4-heptafluorobutoxyalkoxy) biphenyl-4-yl]ethanes and 1-[3-fluoro-4-(1-methylheptyloxycarbonyl) phenyl]-2-[4'-(2,2,3,3,4,4,4-heptafluorobutoxyalkoxy)biphenyl- 4- yl]ethanes have been proposed, checked and compared. The compounds were prepared by Sonogashira coupling of 4-benzyloxy- 4'-ethynylbiphenyl with appropriate 4-halobenzoate esters followed by parallel hydrogenation of ethynylene bridge and debenzylation of hydroxyl group. The 1-[4-(1-methylheptyloxycarbonyl) phenyl]-2-[4'-hydroxybiphenyl-4-yl]ethane and 1-[3-fluoro- 4-(methoxycarbonyl)phenyl]-2-[4'-hydroxybiphenyl-4-yl]ethane thus obtained has been transformed into final products by Mitsunobu reaction with ω-(2,2,3,3,4,4,4-heptafluorobutoxy)alkan-1-ols, followed by the replacing of an ester terminal chain in the case of second method. [ABSTRACT FROM AUTHOR]

We report the results of the optical transmission and the capacitance behavior as a function dc electric field of a pristine liquid crystal and conducting polymer nanotube-liquid crystal composite measured in twisted nematic cells. The threshold and driving voltages have been determined from transmission-voltage curve. There is remarkable reduction in the threshold and driving voltage in the polymer nanotube doped liquid crystal cell which is good from application point of view. The residual dc is also reduced significantly in the doped cell and the reduction is even more than that observed in the carbon nanotube doped same liquid crystal system. [ABSTRACT FROM AUTHOR]