Amphibious sensor of temperature and refractive index based on D-shaped photonic crystal fibre filled with liquid crystal

ABSTRACT

A D-shaped photonic crystal fibre filled with liquid crystal was demonstrated as an amphibious sensor for detection of both temperature and refractive index, when combined with plasma materials. Specifically, the optical component is implanted into a complete optical system ensuring modulation of the external electric field. When the refractive index of the external solution changes from 1.0 to 1.6, the y-polarised mode has a loss spectrum with a wavelength sensitivity of up to 2275 nm/RIU, and the corresponding amplitude sensitivity is ?88.2RIU^?1. When the perceived temperature changes from 15°C to 50°C, the temperature of the sensor is correspondingly expressed as the maximum wavelength sensitivity of 9.09 nm/°C and the amplitude sensitivity of ?0.311°C^?1. In addition, the actual micro-operation processes have been studied in detail, such as polishing depth, coating thickness and coating method. This provides practical ideas for real-time sensing analysis that requires harsh environments.     

Molecular dynamics simulation of polymer dispersed liquid crystal droplets under competing boundary conditions

This paper is devoted to the molecular dynamics simulation of structural organization inside a polydispersed liquid crystal (LC) droplet under competing boundary conditions. The droplet is assumed to be placed at the liquid crystal interface between two different regions of the solid polymer matrix, which accordingly separates the droplet into two hemispheres: the first of these is under radial boundary conditions; the second hemisphere is under bipolar boundary conditions. The droplet is considered as a jagged sphere filled with LC molecules, modelled as classical spins (unit vectors), whose centres of mass are associated with sites of a cubic lattice inside the cavity. The orienting action of the polymer matrix, and hence the resulting boundary conditions, are modelled by the interaction between the internal LC molecules (possessing only orientational degrees of freedom), and those of a delimiting surface layer (a jagged spherical shell), whose orientations are fixed, radial or bipolar, respectively. All interactions are modelled by the short range McMillan pair potential. The molecular orientation inside the LC droplet has been determined for various anchoring strengths of the interaction between internal spins and boundary layers. We have investigated the structure of the spherical defect resulting in the central region of the droplet, as well as of the boojum ‐ like defects existing near the poles of the droplet. It has been found that a change of relative radial and bipolar anchoring strengths can affect both central and boojum ‐ like defects. The effect of an external field on the molecular orientation inside the droplet has also been investigated. It has been found that a sufficiently strong external field increases the radius of the spherical defect placed in the central region of the droplet.     

Molecular dynamics simulation of polymer dispersed liquid crystal droplets under competing boundary conditions

This paper is devoted to the molecular dynamics simulation of structural organization inside a polydispersed liquid crystal (LC) droplet under competing boundary conditions. The droplet is assumed to be placed at the liquid crystal interface between two different regions of the solid polymer matrix, which accordingly separates the droplet into two hemispheres: the first of these is under radial boundary conditions; the second hemisphere is under bipolar boundary conditions. The droplet is considered as a jagged sphere filled with LC molecules, modelled as classical spins (unit vectors), whose centres of mass are associated with sites of a cubic lattice inside the cavity. The orienting action of the polymer matrix, and hence the resulting boundary conditions, are modelled by the interaction between the internal LC molecules (possessing only orientational degrees of freedom), and those of a delimiting surface layer (a jagged spherical shell), whose orientations are fixed, radial or bipolar, respectively. All interactions are modelled by the short range McMillan pair potential. The molecular orientation inside the LC droplet has been determined for various anchoring strengths of the interaction between internal spins and boundary layers. We have investigated the structure of the spherical defect resulting in the central region of the droplet, as well as of the boojum - like defects existing near the poles of the droplet. It has been found that a change of relative radial and bipolar anchoring strengths can affect both central and boojum - like defects. The effect of an external field on the molecular orientation inside the droplet has also been investigated. It has been found that a sufficiently strong external field increases the radius of the spherical defect placed in the central region of the droplet.     

Molecular shape of liquid crystal molecules

It is shown that vibrational spectroscopy can provide information on the molecular structure of complex systems such as liquid crystals. Methods are mentioned and data are reported for dodecyl-cyano-biphenyl and for a thermotropic liquid crystal aromatic polyester.     

Biphotonic recording effect of polarization gratings based on dye-doped liquid crystal films

This study investigates a holographic recording effect of biphotonic polarization gratings (BPGs) written on dye-doped liquid crystal (DDLC) films. One linearly polarized green light (λ_G = 514.5 nm) and a polarization-modulated interference pattern formed by two mutually coherent orthogonal (±45° with respect to the polarization of the green light) polarized red lights simultaneously excite the DDLC films to generate a BPG. The formation of BPGs depends primarily on the dichroism of the dye molecules and a sequence of mechanisms: photoisomerization, anisotropic adsorption and inhibition of dye adsorption. The cis-isomer absorbance-modulated distribution associated with the red polarization-modulation pattern induces the dye adsorption-modulated pattern, in turn, yielding the permanent BPG which generates a modulated twisted nematic (TN) structure pattern in the sample. It is found that each BPG is verified to be electrically switchable and thermally erasable. The switching time is in the order of milliseconds. Additionally, the recording time to form a BPG decreases with increasing intensity of the green pump beam.     

Computer simulation of a real liquid crystal

We carried out a computer simulation study of a liquid crystal using semi-empirical atom-atom potentials (the Lennard-Jones 6-12 modification) with nematic 4-ethoxybenzylidene-4-n-butylaniline as an example. The two stages of the calculations were (1) simulation of the structure of an isolated molecule and (2) Monte Carlo simulation of liquid crystal phase. The energy of the system was calculated as the sum over all atomic pair interactions. The molecular structure preferred in the nematic phase is discussed.     

Dynamic simulation of Pi-cell liquid crystal displays

The dynamics of π-cell liquid crystal displays was studied by detailed computer simulation. The time evolution of the director configuration and the velocity of flow reveals the mechanism of the fast response of π-cells. The effect of pretilt angle on the dynamics of π-cells was also studied.     

High sensitive piezoelectric quartz crystal liquid density sensor

<正>We report for the first time a cleavage phenomenon in the resonant peak of a piezoelectric quartz crystal(PQC) in liquid phase.In the presence of a strong longitudinal wave effect,an additional resonant peak appears in the conductance-frequency curve.With gradually increasing liquid density,the additional peak moves from low to high frequency region then disappears.The frequency of the additional resonant peak is sensitive to the change in liquid density.The frequency shift of the additional peak is linear with the liquid density in a given range.For a 5 MHz PQC with a reflection distance of 16 mm for longitudinal wave,the sensitivity to liquid density is 2.61×10~6 Hz g~(-1) cm~3.The overlap between the primary resonant peak and the additional resonant peak causes a decrease in the intensity of the former and an increase in the intensity of the latter.In a combined impedance analysis method,the changes in surface mass loading,density and viscosity of the liquid were monitored simultaneously by a PQC sensor.     

A two dimensional liquid crystal simulation for thin film transistor liquid crystal displays

Abstract

A two-dimensional liquid crystal simulation, whose electrode configuration corresponds to that in a thin film transistor liquid crystal display (TFT-LCD), was carried out. Simulation results show that the lateral field between buslines and pixel electrode forms a reverse tilt domain. This reverse tilt domain leads to the disclination on the pixel electrode. The distance from the pixel electrode edge to this disclination location depends on the dielectric anisotropy and elastic constant for the liquid crystal. A small dielectric anisotropy or large elastic constant makes this distance small.     

Molecular dynamics simulation of liquid trimethylphosphine

Structural and dynamical properties of liquid trimethylphosphine (TMP), (CH(3))(3)P, as a function of temperature is investigated by molecular dynamics (MD) simulations. The force field used in the MD simulations, which has been proposed from molecular mechanics and quantum chemistry calculations, is able to reproduce the experimental density of liquid TMP at room temperature. Equilibrium structure is investigated by the usual radial distribution function, g(r), and also in the reciprocal space by the static structure factor, S(k). On the basis of center of mass distances, liquid TMP behaves like a simple liquid of almost spherical particles, but orientational correlation due to dipole-dipole interactions is revealed at short-range distances. Single particle and collective dynamics are investigated by several time correlation functions. At high temperatures, diffusion and reorientation occur at the same time range as relaxation of the liquid structure. Decoupling of these dynamic properties starts below ca. 220 K, when rattling dynamics of a given TMP molecules due to the cage effect of neighbouring molecules becomes important.     

液态水的分子动力学模拟

用分子动力学(MD)模拟方法在150~376K的温度范围内对液态水的微正则系统进行了研究。考察了液态水的结构及其性质。模拟采用了由从头算得出的柔性水-水相互作用势MCYL。对时间和空间的平均得出了液态中水分子几何构型及温度改变所引起的液态水结构变化。对径向分布函数gOH, gOO, gHH及配位数的分析表明, 在所考察的温度范围内, 每个水分子与相邻分子形成的氢键数为2~3, 水分子在参与的2个氢键中同时作为授受体。结合对振动谱的研究表明在低温时液态水形成的网络结构可能随温度的升高而形成小的簇结构。     

Electrochemical sensor for cinchonine based on a competitive host-guest complexation

An electrochemical sensor for cinchonine (CCN) using the β-cyclodextrin (β-CD) modified poly(N-acetylaniline) (PAA) electrode has been developed, in which 1,4-hydroquinone (HQ) was chosen as a probe. Complexation of HQ with β-CD modified on the glassy carbon electrode (GCE) was examined by cyclic voltammetry (CV). HQ was included in the cavity of β-CD and reversible voltammograms were observed. In the presence of CCN, a competitive inclusion equilibrium with β-CD was established between HQ and CCN, lowering the peak current of HQ. The decrease in the peak current of HQ is directly proportional to the amount of CCN. Linear calibration plot was obtained over the range from 4.0 × 10⁻⁶ to 8.0 × 10⁻⁵ M with a detection limit (S/N = 3) of 2.0 × 10⁻⁶ M. From the inhibitory effect of CCN on the inclusion of HQ by β-CD, the apparent formation constant of CCN with the immobilized β-CD was estimated. This electrochemical sensor showed excellent sensitivity, repeatability, stability and recovery for the determination of CCN. The response mechanism of the sensor was discussed in detail. The optimum steric configuration of inclusion complex was presented by molecular dynamics simulation.     

Molecular simulation of water behaviors on crystal faces of hydroxyapatite

The water behavior on (001) and (100) crystal faces of hydroxyapatite (HAP) were studied using molecular dynamics (MD) simulations. The study showed that the water molecules between the HAP faces were under conditions of strong electrical field and high pressure, and hence formed 2–3 well-organized water layers on the crystal surfaces. These structured water layers had ice-like features. Compared with the crystallographic [100] direction of HAP, the polarity along the [001] direction was stronger, which resulted in more structured water layers on the surface. The interaction of water molecules with the calcium and phosphate sites at the HAP-water interface was also studied. The results indicated the multiple pathways of water adsorption onto the HAP surfaces. This study revealed the formation and the detailed structure of water layers on HAP surfaces and suggested that the interfacial water played an important role in stabilizing the HAP particles in aqueous solutions. Translated from Chinese Journal of Inorganic Chemistry, 2006, 22(8): 1392–1400 (in Chinese)     

A greener electrochromic liquid crystal based on ionic liquid electrolytes

An electrochromic liquid crystal (ECLC) material composed of only liquid crystal (LC) and ionic liquid (IL) was developed. The LC containing the substituted diphenylacetylene serves as electrochromic (EC) material to realise transmittance and colour change under the direct current (DC) field, while the IL with the designable cation and anion served as electrolyte. Herein, a series of IL electrolytes was screened to investigate how IL tunes the electro-optic performance of the ECLC cell. By testing the electrochemistry window of ILs in EC cells, IL with the [NTf₂]^? anion shows adequate electrochemical stability when the EC material undergoes oxidation and reduction. The electro-optic performance of ECLC containing 1-ethoxy-4-[2-(4-pentylphenyl) ethynyl]-benzene (PEB) and IL was then evaluated by UV-vis spectrometry under the control of an electrochemical work station. Compared with other PEB-IL, PEB-[Bmim][NTf₂] with [Bmim][NTf₂] electrolyte shows a satisfactory transmittance at low operating voltage. Furthermore, Pd NPs in situ formed in [Bmim][NTf₂] reduced the EC potential and improved the light scattering of the ECLC cell. In this work, we also designed a bifunctional device based on polymer dispersed liquid crystal (PDLC) that hosts electrochromic guest molecules, and analysed the electro-optical and electrochromic properties of LC electrolyte mixtures, in order to gain control of the incident daylight and glare in building and automotive applications.     

Molecular dynamics simulation study of the influence of chirality on the stability of the smectic Q liquid crystal phase

The structure of smectic Q (SmQ) liquid crystal phase consisting of a dichiral molecule, called M7BBM7, was studied by submicrosecond molecular dynamics (MD) simulation. A detailed atomic model was used to study the stability of a model SmQ structure proposed by Levelut et al. (Levelut, A.-M.; Hallouin, E.; Bennemenn, D.; Heppke, G.; Lotzsch, D. J. Phys. II 1997, 7, 981) and its difference between (S,S)-, (S,R)-M7BBM7 and racemic mixture systems. Negative values of the fourth-rank orientational order parameter (), which characterize the model SmQ structure, were stably kept up to a 100 ns MD run only in the (S,S)-M7BBM7 system and lost in the other systems. The results correspond well to the marked chiral sensitivity in real systems where only the (S,S)-M7BBM7 system (among the three above-mentioned systems) shows the SmQ phase. Our simulation results imply that the asymmetric intramolecular potentials and resultant chirality-dependent molecular conformations are primarily responsible for keeping the negative values of and the model SmQ structure.     

Molecular dynamics simulation of liquid sulfur dioxide

A previously proposed model for molecular dynamics (MD) simulation of liquid sulfur dioxide, SO(2), has been reviewed. Thermodynamic, structural, and dynamical properties were calculated for a large range of thermodynamic states. Predicted (P,V,T) of simulated system agrees with an elaborated equation of state recently proposed for liquid SO(2). Calculated heat capacity, expansion coefficient, and isothermal compressibility are also in good agreement with experimental data. Calculated equilibrium structure agrees with X-ray and neutron scattering measurements on liquid SO(2). The model also predicts the same (SO(2))(2) dimer structure as previously determined by ab initio calculations. Detailed analysis of equilibrium structure of liquid SO(2) is provided, indicating that, despite the rather large dipole moment of the SO(2) molecule, the structure is mainly determined by the Lennard-Jones interactions. Both single-particle and collective dynamics are investigated. Temperature dependency of dynamical properties is given. The MD results are compared with previous findings obtained from the analysis of inelastic neutron scattering spectra of liquid SO(2), including wave-vector dependent structural relaxation, tau(k), and viscosity, eta(k).     

Molecular dynamics simulation of the nematic liquid crystal phase in the presence of an intense magnetic field

The influence of an intense external field on the dynamics of the nematic liquid crystal phase is investigated using a molecular dynamics simulation for the Gay-Berne nematogen under isobaric-isothermal conditions. The molecular dynamics as a function of the second-rank orientational order parameter P<2> for a system consisting of a nematic liquid crystal in the presence of an intense magnetic field is compared with that of a similar system without the field. The translational motion of molecules is determined as a function of the translational diffusion coefficient tensor and the anisotropy and compared with the values predicted theoretically. The rotational dynamics of molecules is analyzed using the first- and the second-rank orientational time correlation functions. The translational diffusion coefficient parallel with respect to the director is constrained by the intense field, although the perpendicular one is decreased as the P<2> is increased, just as it is in the system without the field. However, no essential effect of the strong magnetic field is observed in the rotational molecular dynamics. Further, the rotational diffusion coefficient parallel with respect to the director obtained from the first-rank orientational time correlation function in the simulation is qualitatively in agreement with that in the real nematic liquid crystalline molecules. The P<2> dependence of the rotational diffusion coefficient for the system with the intense magnetic field shows a tendency similar to that for the system without the field.     

Circularly polarized luminescence based on cholesterol-tetraphenylethylene-perylene liquid crystal

Perylene derivative with circularly polarized luminescence（CPL） at aggregated state was seldom reported due to the strong ACQ（aggregation-caused quench） effect at aggregation. In this work, a novel cholesterol-tetraphenylethylene-perylene derivative（TPE-P） was designed and synthesized in moderate yield. It exhibited liquid crystalline behavior with orderly hexagonal columnar mesophase and good fluorescence emission at long wavelength（600-700 nm） not only in solution but also at aggregated states...     

Molecular dynamics simulations of liquid crystal molecules on a polyimide monolayer

Preliminary results are presented on the molecular dynamics simulations of alignment of the liquid crystal molecule, 4-n-octyl-4'-cyanobiphenyl (8CB), on a polyimide (pyromelltic dianhydride-p-phenylene diamine) oligomer monolayer. We actually simulated a three-layer system, i.e., liquid crystal molecule/polyimide oligomer/a basal plane of graphite. First, simulations of the oligomers adsorbed on graphite were done in order to obtain reasonable adsorption structures, as the pre-stage simulation of the three-layer system. Then, by placing a liquid crystal layer on top, the three-layer system was simulated. The stable liquid crystal alignment direction on the polyimide monolayer was found roughly to be the polyimide chain direction with zero pretilt in this combination of liquid crystal and polymer materials. The calculated adsorption energy of an 8CB molecule to the polyimide monolayer was 128 kJ mol^-1 and the carbonyl group of the polyimide was the main adsorption site.