Liquid Crystal Samples Research Articles

A new strategy to activate liquid crystal polymer samples for electroless copper deposition

ABSTRACTIn order to activate the polymers for electroless copper deposition, an alternative way of sample preparation is demonstrated. The samples are prepared by incorporation of a small amount (<1 wt %) of palladium, nickel, or copper acetate into the molten Liquid Crystal Polymer (LCP) in a blender. Since the blending temperature is kept higher than the decomposition temperature of acetates, the acetates are thermally decomposed during blending, leading to the metallic Pd, Ni, or Cu which are used as activators for electroless deposition. After preparing the samples, electroless copper deposition is successfully realized. The influence of different acetates (Pd, Ni, or Cu acetates) on the deposition is investigated. The copper amount is higher and the deposition kinetics is faster on LCP samples with 0.15 wt % Pd and 0.4 wt % Ni than that with 0.4 wt % Cu. The deposited copper layers are uniform and oxide‐free. Moreover, the possibility to substitute expensive Pd activator by cheaper Ni or Cu is shown. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44397.

Dynamics of the director reorientation in confined nematic liquid crystals imposed by a strong orthogonal electric field

The dynamics of the periodic distortions in confined nematic liquid crystals (LCs) has been investigated theoretically basing on the hydrodynamic theory including the director motion with appropriate boundary and initial conditions. Analysis of the numerical results for the turn-on process provides an evidence for the appearance of the spatially periodic patterns in confined LC film, only in response to the suddenly applied strong electric field. It has been shown that there is a threshold value of the amplitude of the thermal fluctuations of the director over the LC sample which provides the nonuniform rotation mode rather than the uniform one, whereas the lower values of the amplitude dominate the uniform mode. During the turn-off process the reorientation of the director to the direction preferred by the surfaces is characterized by the complex destruction of the initially periodic structure to a monodomain state.

Refractive index and absorption coefficient of blue phase liquid crystal in terahertz band

ABSTRACTThe refractive index and absorption coefficient of blue phase liquid crystals are investigated by terahertz time-domain spectroscopy system. Four phases, including isotropic phase, BPII, BPI, and cholesteric phase are investigated. The refractive index of liquid crystal sample is dependent on the temperature, which is related to the different phases. In our experiment, in the frequency range of 0.2–1.2 THz, the refractive index of BPII and BPI is about 1.620 and 1.625, respectively. For BPII and BPI, the measured absorption coefficients increase with the increase of frequency, with absorption peak appearing at 1.11 and 1.05 THz, respectively. These properties of BPLC provide useful information for BPLC-based terahertz components such as phase shifter, wave-plates and so on.

Solid Phase Extraction and Preconcentration of Trace Gallium, Indium, and Thallium Using New Modified Amino Silica.

Amino silica gel functionalized with 2-hydroxy-5 -(2-hydroxybenzylideneamino)benzoic acid was synthesized, characterized and used as adsorbent for the removal of Ga3+, In3+ and Tl3+ from aqueous solution prior to their determination by flame atomic absorption spectrometry. Experimental parameters that affect the separation process were investigated in both batch and column modes. The maximum adsorption capacities of the sorbent are 61.7 mg g-1, 81.3 mg g-1 and 133.0 mg g-1 for Ga3+, In3+ and Tl3+, respectively. The preconcentration factor is 200 and the limits of detection of Ga3+, In3+ and Tl3+ are 4.10 μg L-1, 1.55 μg L-1 and 1.21 μg L-1, respectively. Interference by Al3+ can be masked by the addition of F-; and that of Fe3+ by its reduction to Fe2+ using 10% ascorbic acid. The method was successfully applied for the determination of these ions in water, sediments and liquid crystal display samples.

Orientational fluctuations and phase transitions in 8CB confined by cylindrical pores of the PET film

Results of optical investigations of the isotropic-nematic and nematic-smectic A phase transitions in porous polyethyleneterephthalate (PET) films filled with octyl-cyanobihenyl (8CB) liquid crystal (LC) are reported. Samples of porous films of thickness 23 µm with normally oriented cylindrical pores of a radius R ranging from 10 nm to 1000 nm were prepared using the track-etched membrane technology. The dynamic light scattering method was used to probe the nematic orientational fluctuations of confined LC samples. The corresponding relaxation time τ was measured as a function of R and temperature T at slow enough cooling rates (0.3–0.6 K/h) to locate the phase transition temperatures. Changes in τ(T) dependencies relatively sensitivity fingerprint the LC phase transformations. Experimental results are analysed using the Landau-de Gennes-Ginzburg phenomenological approach.

Orientational order parameter determination of the liquid crystal: 4 propyl paraethoxy phenyl cyclohexyl carboxylate by X-ray studies

ABSTRACTThe compound 4 propyl paraethoxy phenyl cyclohexyl carboxylate (code name D302) is a member of a homologous series and exhibits liquid crystalline (nematic) behavior in the temperature range 48°C to 78°C. An experiment has been set up for conducting X-ray studies of liquid crystal samples at various temperatures. From X-ray studies conducted at different temperatures on D302, the apparent molecular length and inter-molecular distance and their temperature dependence have been determined. The variation of the orientational-order parameter <P2>xray has been determined from the intensities of the scanned X-ray photographs taken at different temperatures. The results have been compared with the<P2>opt values obtained by us from birefringence studies.

Perturbed hedgehogs: continuous deformation of point defects in biaxial nematic liquid crystals

A spherically symmetric isolated point defect in a 3D uniaxial nematic liquid crystal sample is often called a {\it radial hedgehog}. We use topological methods to describe local configurations of uniaxial and biaxial states into which a hedgehog naturally deforms under small perturbations: these include the biaxial torus and split core configurations studied in the literature using analytical and numerical methods. The topological results here take no account of the governing physical laws but provide a library of options from which the physics must make a choice.

Electric-field-induced weakly chaotic transients in ferroelectric liquid crystals.

Nonlinear dynamics induced in surface stabilized ferroelectric liquid crystals by strong alternating external electric fields is studied both theoretically and experimentally. As has already been shown, molecular reorientations induced by sufficiently strong fields of high-enough frequencies can reveal a long transient behavior that has a weakly chaotic character. The resulting complex dynamics of ferroelectric liquid crystals can be considered not only as a consequence of irregular motions of particular molecules but also as a repercussion of a surface-enforced partial decorrelation of nonlinear molecular motions within smectic layers. To achieve more insight into the nature of this phenomenon and to show that the underlying complex field-induced behavior of smectic liquid crystals is not exceptional, ranges of system parameters for which the chaotic behavior occurs are determined. It is proved that there exists a large enough set of initial phase trajectory points, for which weakly chaotic long-time transitory phenomena occur, and, thereby, it is demonstrated that such a chaotic behavior can be regarded as being typical for strongly field-driven thin liquid crystal systems. Additionally, the influence of low-amplitude random noise on the duration of the transient processes is numerically studied. The strongly nonlinear contribution to the electro-optic response, experimentally determined for liquid crystal samples at frequencies lower than the actual field frequency, is also analyzed for long-time signal sequences. Using a statistical approach to distinguish numerically response signals of samples from noise generated by measuring devices, it is shown that the distribution of sample signals distinctly differs from the device noise. This evidently corroborates the occurrence of the nonlinear low-frequency effect, found earlier for different surface stabilized liquid crystal samples.

Vibrational mid-infrared photothermal spectroscopy using a fiber laser probe: asymptotic limit in signal-to-baseline contrast.

We report on a mid-infrared photothermal spectroscopy system with a near-infrared fiber probe laser and a tunable quantum cascade pump laser. Photothermal spectra of a 6μm-thick 4-octyl-4'-cyanobiphenyl liquid crystal sample are measured with a signal-to-baseline contrast above 103. As both the peak photothermal signal and the corresponding baseline increase linearly with probe power, the signal-to-baseline contrast converges to an asymptotic limit for a given pump power. This limit is independent of the probe power and characterizes the best contrast achievable for the system. This enables sensitive quantitative spectral characterization of linear infrared absorption features directly from photothermal spectroscopy measurements.

Comparative study of low frequency dielectric properties of Hexyloxybenzylidine hexylaniline and Heptyloxybenzylidine hexylaniline

This article presents a comparative study of low frequency dielectric properties of two Alkyloxybenzylidine alkylaniline compounds—Hexyloxybenzylidine hexylaniline (6O.6) and Heptyloxybenzylidine hexylaniline (7O.6). Dielectric study is made by using cells with ITO coated surface pretreated with polyvinyl alcohol as the aligning layer. We have found that the switching of dielectric anisotropy from negative to positive value is related to the change in orientation of alkyloxy dipole. It indicates 6O.6 (and lower members) to be negative dielectric anisotropic material while 7O.6 (and higher members) to be positive dielectric anisotropic materials. Further comparative study on the interfacial polarization between the two types of interfaces (PVA-6O.6 and PVA-7O.6) with different relaxation times support the differences of the two liquid crystal samples. The dc electric field characteristics of the two samples are drastically different in behaviour and can be explained satisfactorily on the interplay between the dipole orientation and the ionic motion.

Thermo-optical properties and nonlinear optical response of smectic liquid crystals containing gold nanoparticles

The present work is devoted to the study of the thermo-optical and nonlinear optical properties of smectic samples containing gold nanoparticles with different shapes. By using the time-resolved Z-scan technique, we determine the effects of nanoparticle addition on the critical behavior of the thermal diffusivity and thermo-optical coefficient at the vicinity of the smectic-A-nematic phase transition. Our results reveal that introduction of gold nanoparticles affects the temperature dependence of thermo-optical parameters, due to the local distortions in the orientational order and heat generation provided by guest particles during the laser exposure. Further, we show that a nonlinear optical response may take place at temperatures where the smectic order is well established. We provide a detailed discussion of the effects associated with the introduction gold nanoparticles on the mechanisms behind the thermal transport and optical nonlinearity in liquid-crystal samples.

Effect of multi wall carbon nanotube on electrical properties 4-[4-((S)-Citronellyloxy)benzoyloxy]benzoic acid liquid crystal host

Dielectric properties, conductivity mechanisms and current–voltage characteristics of Multi Wall Carbon Nanotube (MWCNT) doped and pure Liquid Crystal (LC) material was investigated using impedance spectroscopy method in the frequency range of 100 Hz to 15 MHz. Liquid crystalline material, 4-[4-((S)-Citronellyloxy)benzoyloxy]benzoic acid (CBBA) as a host material and MWCNT was used as doping material in this study. In order to observe the effects of doping MWCNT into LC on dielectric properties, an MWCNT material was doped into CBBA structure with 1 wt%. Real part of dielectric constants (ɛ′), imaginary part of dielectric constant (ɛ′′), i.e. dielectric loss, dissipation factor/dielectric loss tangent (tanδ) were obtained for the pure and doped LC samples. In addition, dielectric strength (Δɛds), negative dielectric anisotropy (Δɛda), absorption coefficients (α) and relaxation times (τ) were calculated from the empirical data. I–V characteristics of pure LC and doped LC structures were carried out at micro-current levels by current–voltage measurements.

Dielectric relaxation in non-polar nematic liquid crystal devices

We investigate the dielectric relaxation in non-polar nematic planar aligned liquid crystal samples by means of both dielectric spectroscopy and a transient current method. The dielectric functions, obtained by the impedance data, are modeled by the modified Havriliak-Negami method, which allows to determine spectra in terms of permittivity, conductivity and dielectric relaxation. Further information on the involved electric charge and the ion mobility is achieved by means of current measurements. The outcomes demonstrate that the effective relaxation times originate from ionic polarization and depend on the interfaces properties, pointing out the influence of the layered structure.

Thermally excited fluid flow in a microsized liquid crystal channel with a free surface

The temperature-induced reorientation dynamics in microsized liquid crystal (LC) channel with a free LC/vacuum interface has been investigated theoretically based on the hydrodynamic theory including the director motion, the thermally excited fluid flow v, and the temperature T redistribution, produced by induced heating in the interior of the LC sample. Analysis of the numerical results shows that due to interaction between ∇T and the gradient of the director field ∇nˆ in the LC channel bounded by the free LC/vacuum interface, a thermally excited vortical fluid flow is maintained in the vicinity of the heat source. Calculations also show that in the case of the fast heating, the LC sample settles down to three-vortical flow regime, whereas in the case of the slow heating, the LC material settles down to bi-vortical flow regime. As for nematogenic material, we have considered the LC channel to be occupied by 4-n-pentyl-4′-cyanobiphenyl and investigated the effect of both ∇nˆ and ∇T on the magnitude and direction of v, as well as on the height of the LC film on the solid surface, for a number of heating and hydrodynamic regimes.

P‐94: Fast Response Time of Liquid Crystal using a Nanofiber and Polyimide Alignment Mixture

We studied about the electro‐optical properties of nematic liquid crystal samples aligned with a nonofibers (NFs)‐polyimide (PI) mixtures. The sample coated with NFs‐PI mixture showed a faster falling time than the pure PI sample. The falling time of the sample coated with 1 wt% NFs was about 20% faster than the pure PI sample. The elastic constant and the order parameter of the NFs‐PI samples were also larger than the pure PI sample.

Electric and magnetic fields in photoalignment of liquid crystals

AbstractThe results of investigation of slow surface dynamics (easy axis gliding), induced by secondary illumination of photoaligned substrates with linearly polarized UV or blue light in the presence of electric (magnetic) fields, are presented for the first time. The initial surface orientation of nematic liquid crystal (NLC) was provided, in accordance with the standard photoalignment technique, via preliminary UV treatment of the glass substrates coated by sulfonic azo‐dye SD1 film. The experiments fulfilled for the two geometries, A and B, corresponding to the normal (A) and parallel (B) orientation of fields relatively to liquid crystal (LC) layer, revealed different effects induced by electric (magnetic) fields. For geometry A, strong electric field applied, in combination with a linearly polarized blue light, to the planar layer in a sandwich‐like LC cell with two photoaligned substrates results in simultaneous reorientation of easy axis on both substrates. It demonstrates the possibility of an azimuthal rotation of monodomain planar samples of LCs. For geometry B, usage of “in‐plane” electric (magnetic) fields in the cell, composed of photoaligned and rubbed substrates, speeds up reorientation process of NLC easy axis respectively to pure light‐induced reorientation. It provides electric control of operating times in previously proposed optical rewritable technology.

Thermally induced light-scattering effects as responsible for the degradation of cholesteric liquid crystal lasers.

We have studied the degradation process of the laser emission in a cholesteric liquid crystal laser. We have found that there exists a negative correlation between the laser efficiency and the amount of light scattered by the liquid-crystal sample in the illuminated area. The growth of scattering is attributed to the appearance of small imperfections generated in the sample as a result of certain thermal processes that involve the dye molecules. The scattering implies an increase of the coefficient of distributed losses, which is the main response of the rise of the laser threshold.

Nano-Structural Analysis of a Lyotropic Liquid Crystal (TTAB + water + decanol ternary) System by Salt (NH4Br) Addition

In the present study, the ionic effect of salt addition to a lyotropic liquid crystal (LLC) system was investigated. NH4Br salt was added to TTAB + water + decanol ternary system and the structural changes in lyotropic phases were characterized. First, phase transitions were illustrated by polarized microscope and secondary, small-angle x-ray scattering was used as an analytical method to determine the nano-structured mesophases of the newly prepared liquid crystal samples. The expected fibrous structures were characterized by the form factor of polydisperse oblate ellipsoids. The self-assembled networks related with these ellipsoids were also explained with hexagonal, distorted hexagonal, and lamellar formations.

Molecular organization of nematic liquid crystals between concentric cylinders: role of the elastic anisotropy.

The orientational order in a nematic liquid crystal sample confined to an annular region between two concentric cylinders is investigated by means of lattice Monte Carlo simulations. Strong anchoring and homeotropic orientations, parallel to the radial direction, are implemented at the confining surfaces. The elastic anisotropy is taken into account in the bulk interactions by using the pair potential introduced by Gruhn and Hess [T. Gruhn and S. Hess, Z. Naturforsch. A 51, 1 (1996)] and parametrized by Romano and Luckhurst [S. Romano, Int. J. Mod. Phys. B 12, 2305 (1998); Phys. Lett. A 302, 203 (2002); G. R. Luckhurst and S. Romano, Liq. Cryst. 26, 871 (1999)], i.e., the so-called GHRL potential. In the case of equal elastic constants, a small but appreciable deformation along the cylinder axis direction is observed, whereas when the values of K(11)/K(33) if K(22)=K(33) are low enough, all the spins in the bulk follow the orientation imposed by the surfaces. For larger values of K(11)/K(33), spontaneous deformations, perpendicular to the polar plane, increase significantly. Our findings indicate that the onset of these deformations also depends on the ratio K(22)/K(33) and on the radius of the cylindrical surfaces. Although expected from the elastic theory, no tangential component of the deformations was observed in the simulations for the set of parameters analyzed.

Spin squeezing in a quadrupolar nuclei NMR system.

We have produced and characterized spin-squeezed states at a temperature of 26 °C in a nuclear magnetic resonance quadrupolar system. The experiment was carried out on 133Cs nuclei of spin I=7/2 in a sample of lyotropic liquid crystal. The source of spin squeezing was identified as the interaction between the quadrupole moment of the nuclei and the electric field gradients present within the molecules. We use the spin angular momentum representation to describe formally the nonlinear operators that produce the spin squeezing on a Hilbert space of dimension 2I+1=8. The quantitative and qualitative characterization of this spin-squeezing phenomenon is expressed by a squeezing parameter and squeezing angle developed for the two-mode Bose-Einstein condensate system, as well as by the Wigner quasiprobability distribution function. The generality of the present experimental scheme points to potential applications in solid-state physics.