Liquid crystal material with gold nanoparticles as optical sensors active medium for the amino acids detection

Abstract

In the article, the possibility of using the cholesteric liquid crystal mixture doped by the gold nanoparticles as an active medium of optical amino acid sensors is shown. The BLO-62 and the 5CB were used as a cholesteric liquid crystal and a nematic liquid crystal correspondingly. This mixture was doped by the gold nanoparticles. The method of gold nanoparticles synthesis is considered and their parameters are determined. Studies on the spectral characteristics of the investigated materials have shown that the addition of gold nanoparticles to the system leads to a significant decreasing in the spectral characteristic steepness and give the possibility of expanding the measurement range of amino acid concentration.     

名义纯及掺杂铌酸锂晶体内偏置场的实验研究

铌酸锂晶体的内偏置场对铁电应用、电光应用和非线性光学应用等均有直接影响。本工作建立了铌酸锂(LN)晶体内偏置场测试方法,对同成分铌酸锂(CLN)晶体、近化学计量比铌酸锂(nSLN)晶体、掺杂铌酸锂(doped LN)晶体的内偏置场和矫顽场进行测量。结果表明,CLN晶体内偏置场最高(E_int=2.53 kV/mm),nSLN晶体的内偏置场大幅降低,其中富锂熔体法生长和气相输运平衡(vapor transport equilibration, VTE)法结合得到的nSLN晶体的内偏置场最小,与CLN晶体相比降低了约两个数量级;掺杂铌酸锂晶体的内偏置场与CLN晶体相比也普遍降低,其中掺6.5%(摩尔分数)Mg的CLN晶体的内偏置场约为CLN晶体的四分之一,掺7%(摩尔分数)Zn的CLN晶体的内偏置场约为CLN晶体的六分之一。最后对组分和掺杂影响内偏置场的因素进行了简要分析。     

掺三氟乙酸TGS晶体生长及其性能研究

本文以三氟乙酸作为掺质,分别按4.4mol%、9.4mol%、13.4mol%、18.4mol%的配比进行了掺质TGS晶体生长,并对其作X射线粉末衍射分析及晶体热释电性能的测试。结果表明,三氟乙酸的掺入虽然使热释电性能有一定程度下降,但却使得晶体铁电-顺电相转变延迟,提高了晶体的居里点,并产生了一定的内偏压场。     

Modification in dielectric properties of SWCNT doped ferroelectric liquid crystals

Effect of single walled carbon nanotubes (SWCNT) in ferroelectric liquid crystal (FLC) geometry has been studied for low and high concentrations of dopant. The results are compared with the characteristics of pure FLC system. An appreciable change in dielectric permittivity, relaxation behavior and other vital parameters has been observed for SWCNT doped FLC system, which shows the adaptability of carbon nanotubes with that of pure FLC molecule. Under high electric field, highly concentrated SWCNT doped FLC shows enormously large values of dielectric loss. This is due to the high conductivity of SWCNT at higher electric field. Interestingly, such effect is not much prominent for the low concentration of the SWCNT doped FLC system.     

Ferroelectric Liquid Crystals

A review of the ferroelectricity in liquid crystals is given, beginning with a discussion of the symmetry properties allowing a macroscopic polarization in some of the more ordered liquid crystal phases. The fundamental mechanisms behind the dipolar ordering are discussed in some detail. The two linear electric effects, ferro- and flexo-electricity, give rise to completely different phenomena. In the smectic C phase there is one ferroelectric coefficient and nine flexoelectric ones, giving independent contributions to the polarization of the medium. We further discuss helical and non-helical structures, doped and intrinsic infinite-pitch ferroelectrics and, finally, the rich potential of liquid crystal ferroelectrics aligned in the »book-shelfgeometry» for fast electro-optic devices.     

Field-Induced Orientation Transition in Ferroelectric Liquid Crystals

Static and dynamic effects of a fast bistable device containing a ferroelectric liquid crystal are investigated theoretically. The switching mechanisms are different at low and high electric fields. There is a critical voltage which separates a bulk switching regime from the regime of domain wall motion. This threshold is determined as a function of physical device parameters.     

Dielectric Spectroscopy of Ferronematics Based on 6CHBT Liquid Crystal

In our study, the dielectric behaviour of the rod-like liquid crystal (6CHBT) doped with magnetic nanoparticles of spherical shape was investigated by means of dielectric spectroscopy in the frequency range from 20 Hz to 2 MHz. A low frequency dielectric dispersion in the nematic and isotropic phases of the pure liquid crystal (LC) has been assigned to the space charge polarization. After doping the host LC with the magnetic nano particles, a nearly Debye-like relaxation process was observed with the temperature dependence obeying the Arrhenius law. Considering a possible electric double layer formation on the particle surfaces, the detected relaxation process in the doped LC can be associated with the electric double layer polarization. The experimental results point out that in the measured frequency range the space charge and interfacial effects constitute the main dielectric response. Any anchoring effects were not observed and are therefore expected to appear in higher frequencies.     

Dynamic Layer Response under Electric Field in Antiferroelectric Liquid Crystal Cells Measured by Synchrotron Microbeam Time Resolved X-Ray Diffraction

Abstract

Direct observation of the local layer response of an antiferroelectric liquid crystal to the step form electric field has been carried out by a time resolved synchrotron X-ray micro diffraction measurement. When an electric field was changed from high voltage to OV, corresponding to the ferroelectric to antiferroelectric phase transition, the local layer transformed from the bookshelf to the quasi-bookshelf structure within 0.3 ms. The horizontal chevron structure was found in both the phases, though the decrease in the horizontal chevron angle was observed during a period of 0.2 ms after turning off the electric field. In the antiferroelectric to ferroelectric phase transition process (from OV to high voltage), the layer structure transformed to the bookshelf within 0.04 ms.     

The Behaviour of Thin Samples of Ferroelectric Liquid Crystals

On a ferroelectric liquid crystal DOBAMBC transitions between helical and twisted structures are observed if changing the temperature. The twisted structure appears when the helical pitch becomes comparable to the sample thickness, From the switching process of the twisted DOBAMBC samples in an electric field the polarity of surface layers is determined. Low signal di- electric permittivity shows an increase below the transition to the ferroelectric phase, which is a consequence of the twisted structure deformation in the electric field.     

Self-assembled PEDOT nanoropes: Materials for improving electro optical properties of liquid crystal

A ropelike conducting polymer nanostructure was synthesized in this work. 3,4-ethylenedioxythiophene (EDOT) was polymerized in presence of a nematic liquid crystal (5CB) giving rise to the PEDOT nanoropes with diameter 10–20 nm. UV–Vis spectra of the nanoropes was comparable with the lightly doped bulk PEDOT. However, unlike the bulk polymer, the nanoropes or helical nanofibres, separated from the medium could be re-dispersed in chloroform and could be blended with 5CB. Electro optical properties of 5CB were remarkably modified after incorporation of PEDOT nanoropes. The residual current for optical transmission, threshold voltage for Freedericksz transition and capacitance hysteresis of 5CB were substantially lowered after nanorope incorporation.     

Dielectric,piezoelectric, elastic properties and internal friction of TGSe crystals with large unipolarity

In this work we have studied influence of temperature and external electric field on dielectric, elastic, piezoelectric properties and internal friction of D, L-α-alanine doped triglycine selenate crystals. Experimental result analysis allows to conclude that ferroelectric materials with stable physical properties may be created on doping crystals foundation.     

Dielectric characteristics of Ce3+ doped Sr0.61Ba0.39Nb2O6 with Cole‐Cole plots technique

In this paper, we have investigated two‐relaxator mechanism and dielectric characteristics of Ce³⁺ doped Sr_0.61Ba_0.39Nb₂O₆ with dielectric spectroscopy measurements. The crystal undergoes a ferroelectric phase transition at 340 K. The temperature dependence of the real and imaginer part of the complex dielectric susceptibility in vicinity of ferroelectric‐paraelectric phase transition has been studied in the frequency region 0.1 kHz–10 MHz. The measurements of the dielectric constant of the real and imaginer parts show strongly frequency dependence. The investigations of the dielectric constant revealed a non‐Debye type dielectric relaxation for Ce⁺³ doped SBN61 by using Cole‐Cole plots. It reveals the coexistence of the two dielectric relaxators in vicinity of the phase transition. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Electro-Optical Properties of Doping Polycyclic Aromatic Hydrocarbon Liquids in Twisted Nematic Liquid Crystals

In this paper, doping liquid materials to enhance the electro-optical (EO) properties of twisted nematic liquid crystals (NLCs) was presented. Two polycyclic aromatic hydrocarbon (PAH) liquids, toluene and 1-methylnaphthalene, were chosen as dopants in order to lower the driving voltage and response time of the NLCs. We find that the main reason of this phenomenon is due to a large amount of reduction in the rotational viscosity of PAH liquids doped NLCs. Without the drawbacks of aggregation that the solid nanoparticles could have, the method of doping liquids provides a more reliable choice for applications in various LC display systems.     

Blue phase liquid crystals stabilized by graphene oxide modified with aminoalkyl group

In the present work, the graphene oxide/blue phase liquid crystal composites and long aminoalkyl chains functionalized graphene/blue phase liquid crystal composites were prepared by doping the additives into a blue phase exhibiting liquid crystal host. It is found that the blue phase temperature range could be widened by dispersing a small amount of functionalized graphene. It suggests that anisotropic two-dimensional flake nanoparticles may be of great usefulness for stabilizing blue phases.     

Yb3+掺杂稀土钽铌酸盐的晶体场从头计算研究

Yb³⁺掺杂晶体材料是重要的激光材料,在超短脉冲激光、大功率激光等领域有重要应用前景,但长期以来很难通过实验拟合确定Yb3+晶体场参数,尤其是低对称体系,从头计算是解决此问题的重要途经.本文介绍了适合计算稀土离子掺杂晶体的从头计算DV-Xα方法和有效哈密顿量模型,用该方法计算了Yb³⁺掺杂M型和M'型钽铌酸盐的晶场参数和旋轨耦合参数,得到的能级结构和实验能很好地符合,并发现了Yb³⁺掺杂钽铌酸盐的晶场强度参数随稀土原子序数呈现规律变化.表明结合DV-Xα计算和有效哈密顿量方法是计算Yb³⁺掺杂低对称钽铌酸盐晶体场的有效途径,结果显示Yb3+掺杂钽铌酸盐晶体有望成为新型全固态激光工作物质.     

Dynamics of the Reorientation of a Ferroelectric Liquid Crystal Under an Electric Field Studied by Time-Resolved Optical Waveguide Spectroscopy

Abstract

The dynamic structure and molecular reorientation of a ferroelectric liquid crystal induced by an alternating electric field have been investigated by time-resolved optical waveguide spectroscopy (TROWS) in which the transient waveguide mode patterns were recorded as a function of both time and angle of incidence of a probe beam. A ferroelectric liquid crystal, 4-(2S, 3S)-[2-chloro-3-methylpentanoyloxy]-4′-octyloxybiphenyl (3M2CPOOB) was utilized, which showed a fast response to an external electric field in the order of a microsecond. Under a high electric field, it forms the so-called bookshelf structure in which the director of 3M2CPOOB is tilted by 22.5° away from the smectic layer normal in the SmC* phase. Time-resolved waveguide mode patterns were successfully obtained with a time-resolution of 1.0 μs which enabled us to determine the transient features of dielectric tensor of 3M2CPOOB molecules in three dimensional coordinate system. A model that the molecular reorientation coupled with the layer buckling and the rotation around the cone was proposed from the quantitative analysis of the TROWS data.     

Acid mediated tunability of stimulated laser emission from dye doped chiral microdroplets

Abstract

In the last decade, the possibility to use liquid crystal droplets as optical micro-cavities and lasers has attracted much attention since it paves the way for many applications in the field of sensors or tunable photonics. Several techniques can be used to obtain small micro-resonators as, for example, dispersing a cholesteric liquid crystal inside an immiscible isotropic fluid to create an emulsion. Since liquid crystals are extremely sensitive to external factors as temperature or external fields, laser tuning can be easily achieved. Here, we report on the possibility to tune the laser emission from dye doped cholesteric liquid crystals microdroplets dispersed in a glycerol matrix in presence of nitric acid molecules in the emulsion. Using a fluorescent dye with pH dependent optical properties, the emitted laser wavelength can be tuned in a range of 60?nm. This effect could find applications for the development of spectroscopy based sensors.     

FLEXOELECTRIC INSTABILITY IN NEMATIC LIQUID CRYSTAL BETWEEN COAXIAL CYLINDERS

Abstract

The stability of the equilibrium configurations of a nematic liquid crystal confined between two coaxial cylinders is analysed when a radial electric field is applied and the flexoelectric effect is taken into account. The threshold for perturbations depending only on the radius r in the cylindrical coordinate system and strong boundary conditions is studied. A new type of orientational transition caused by pure flexoelectric effect is found.     

Polystyrene Derivative Films for Liquid Crystal Alignment

We studied the alignment of liquid crystal molecules on rubbed, thin polymer films of polystrene and its derivatives. Liquid crystal molecules were aligned perpendicular to the rubbing direction, although the polymer main chains of rubbed films were oriented along the rubbing direction. The alignment of the liquid crystal depended on the choice of side phenyl groups of polystyrene derivatives, and the pretilt angle varied with the type and the position of the substituents that were introduced into the side phenyl groups. Homogeneous alignment for ferroelectric liquid crystal was obtained by using poly(NO₂ styrene), poly(p-OH styrene) and poly(4-vinylpyridine) films, which have relatively high β-dispersion and glass transition temperatures.     

Crystal growth and electric‐property change by rubidium or cesium doping on potassium‐sodium‐niobate

Alkali metals (Na, Rb or Cs) co‐doped with fiber‐ and bulk‐shaped KNbO₃ single crystals were grown using two original methods by means of doping together of small ionic Na and large ionic Rb or Cs into KNbO₃. Single‐phase crystals could be grown with an orthorhombic system at room temperature as well as pure KNbO₃. Piezoelectric and ferroelectric property changes by the co‐doping of Rb or Cs with Na were estimated using d₃₃ values and a polarization‐electric field hysteresis curve in fiber‐ and bulk‐shaped crystals. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)