NLC Layer Research Articles

A Single‐Step Dual Stabilization of Smart Window by the Formation of Liquid Crystal Physical Gels and the Construction of Liquid Crystal Chambers

AbstractSmart windows are very attractive because they not only provide comfortable indoor conditions for cars and buildings, but also protect privacy. However, current smart windows have problems such as high energy consumption, slow response time, and poor stability. To solve these problems, a single‐step dual stabilization (SSDS) is newly proposed for the fabrication of robust liquid crystal (LC) smart windows switching fast at low voltage. Upon irradiating ultraviolet light on the selected area of the nematic (N) LC optical cell with photoisomerizable macrogelators (B3AZ) and photopolymerizable monomers, NLC physical gels (LCPGs) and partition walls are simultaneously constructed. LCPGs play a role of light shutter under a low electric field (9.6 Vpp) which is ten times lower than that of the conventional polymer‐stabilized LC‐based smart windows. Partition walls constructed by the selected area photopolymerization significantly enhance the mechanical stabilities. Based on the experimental results, it is realized that the NLC layer generated near the partition walls makes the LCPGs respond to a low voltage. Robust SSDS smart windows could open new doors for the development of high‐performance smart windows.

Numerical investigation of nematic liquid crystals in the THz band based on EIT sensor

This paper introduces the concept of electromagnetically induced transparency (EIT) into the permittivity extraction of an anisotropic material-nematic liquid crystal (NLC). A novel two-step strategy is presented to extract the complex permittivity of the NLC at the THz band, which evaluates the relative permittivity tensor from the resonant frequencies and then determines the loss tangent from the quality factor Q of the EIT sensor. The proposed method features high accuracy due to the sharp resonance of the EIT sensor and also high robustness to the thickness of the NLC layer because only amplitude rather than phase information of the transmission coefficients is required. The NLC filled EIT sensor shows a sensitivity of 56.8 μm/RIU (the resonance wavelength shift over the refractive index change unit (RIU)) and Figure of Merit (FoM) of 6.92. The uncertainty of the proposed technique in the relative permittivity and loss tangent is 3% and 8.2%, respectively.

Interaction of electromagnetic waves in nematic waveguide

ABSTRACTControlled by an electric field, the interaction of two coupled TE-modes at the dynamic grating in a planar waveguide with a thin layer of nematic liquid crystal has been studied theoretically. The dynamic grating is induced by an external electric field due to the periodicity of the anchoring energy of nematic with waveguide surface. Metal and dielectric waveguides have been studied. The transmission of TE-modes and its reflection from the periodic structure of the nematic layer have been investigated. The intensity of a signal- mode at the output of the waveguide has been calculated. The dependence of intensity on the anchoring energy amplitude and modulation period, dimensions of the nematic layer and an external electric field has been analyzed. It was shown that the frequency interval of a TE-mode reflection expands with increasing of the electric field. The primary maximum of the reflected mode intensity, as function of the nematic layer length, increases monotonously with growing s number of anchoring energy periods placed on the layer length. The primary peak reaches the largest value of 1 for s ∼ 10÷100 (metal waveguide) and for s ∼ 1000 (dielectric waveguide). The same dependence for the signal-mode, which propagates through the NLC layer, has nonmonotonous form and a complete energy exchange is reached only for certain values of s and the length of the nematic layer.

SPATIALLY MODULATED STRUCTURES IN NEMATIC LIQUID CRYSTAL UNDER OSCILLATORY COUETTE FLOW AT ULTRALOW FREQUENCIES

The distortion of homeotropic structure of nematic liquid crystal under the influence of periodic shear at ultralow frequencies is theoretically described. It is shown that periodic shear action results in spatially modulated structure in NLC layer. Threshold shear amplitude and spacial periodicity of new molecular orientational structure are found on the base of nonlinear nematic liquid crystal hydrodynamic equations using Galerkin method. Theoretical analysis shows that at low frequencies threshold shear amplitude does not depend on frequency and the spatial period of the order of NLC layer thickness. Theoretical results are compared with experimental data.

Photonic density and nonreciprocal optical properties in chiral liquid crystals

Nonreciprocal optical properties of anisotropic (nano-film) heterostructures made of a cholesteric and nematic liquid crystal (CLC-NLC) layers are studied. Namely, a NLC-CLC (and CLC-NLC) structures are considered in which the NLC layer is a quarter-wave plate. The problem is exactly solvable by Ambartsumians’ modified layer addition and Mullers’ transfer-matrix methods. The peculiarities of the polarization dependent properties, such as the photonic density of states, reflection spectra, the polarization plane rotation and ellipticity spectra are investigated. It is shown that such a system canwork as a light modulator, an element for obtaining linearly polarized light with an electrically tunable polarization plane rotation, or a transformer of non-polarized source into linearly polarized light. The analysis of the optical properties in investigated structures can be used for design of perspective optical diodes, microlasers and multifunctional elements on chiral liquid crystals with electrically tunable polarization plane rotation and field controlled light polarization.

The application of NLC for detecting solid crystals surface homogeneity

The goal of the paper is to demonstrate wide fields of new polarizing microscope application based on nematic liquid crystals (LCs) for detecting different solid crystals surface inhomogeneities. Optical polarizing microscope (OPM) based on LCs makes possible to observe the invisible physical fields' distribution on the objects' surfaces. The OPM novelty consists in LC spatial light modulator (SLM) introduction in optical scheme to detect local deformations in real time. LC SLM applied as recording media has to be in direct contact with the surface under investigation. It gives the possibility to detect the invisible physical fields on the surface: intermolecular interactions, electrical, magnetic fields, etc.The theory of LC layer deformations was developed to find the relation between real size of structural defect D and the size of its image D' visualized with NLC layer. OPM method was used for detecting different aspects of surface inhomogeneities for different types of solid crystals. The new results were obtained for twinning boundaries in piezo quartz resonator having industrial application. LC SLM demonstrates non destructive method and better accuracy in comparison with etching, and the simplicity in comparison with x-radiation detecting. LC SLM may be combined with interference, phase-contrast and even near-field microscopes.

Mesospheric dust and its secondary effects as observed by the ESPRIT payload

Abstract. The dust detector on the ESPRIT rocket detected two extended dust/aerosol layers during the launch on 1 July 2006. The lower layer at height ~81.5–83 km coincided with a strong NLC and PMSE layer. The maximum dust charge density was ~−3.5×109 e m−3 and the dust layer was characterized by a few strong dust layers where the dust charge density at the upper edges changed by factors 2–3 over a distance of ≲10 m, while the same change at their lower edges were much more gradual. The upper edge of this layer is also sharp, with a change in the probe current from zero to IDC=−10−11 A over ~10 m, while the same change at the low edge occurs over ~500 m. The second dust layer at ~85–92 km was in the height range of a comparatively weak PMSE layer and the maximum dust charge density was ~−108 e m−3. This demonstrates that PMSE can be formed even if the ratio of the dust charge density to the electron density P=NdZd /n_e≲0.01. In spite of the dust detector being constructed to reduce possible secondary charging effects from dust impacts, it was found that they were clearly present during the passage through both layers. The measured secondary charging effects confirm recent results that dust in the NLC and PMSE layers can be very effective in producing secondary charges with up to ~50 to 100 electron charges being rubbed off by one impacting large dust particle, if the impact angle is θi≳20–35°. This again lends support to the suggested model for NLC and PMSE dust particles (Havnes and Næsheim, 2007) as a loosely bound water-ice clump interspersed with a considerable number of sub-nanometer-sized meteoric smoke particles, possibly also contaminated with meteoric atomic species.

LC Vision Application to Solution Components Structure Investigation

For detecting the solution quality of different materials we suggested to study their solid components structure with NLCs. The operation process consists of solution drying, thin NLC layer application on solid components and imaging study of deformed NLC structures with polarizing microscopy and software that keep the information on solid components structure. We present new achievements in medicine to illustrate the results of non-invasive detecting of some cancer particularities and erythrocytes pathology. For perfume products we suggest new criterion for detecting scents smell durability. In beverage foods we suggest new technology to examine the difference between original products and counterfeit samples.

Light Self-Action in NLCs with Orientational and Thermal Nonlinearities

The properties of a light beam passed through an NLC layer with positive orientational nonlinearity and then reflected from the NLC–substrate interface have been experimentally studied. The divergence and the intensity profile of this beam were found to be quite different from those of the beam transmitted through the NLC cell. It is shown that the aberrational pattern in the cross-section of the reflected beam and the dynamics of its formation can be used to study the orientational nonlinearity even in the presence of thermal effects.

Orientational Dynamics in Nematic Liquid Crystal under Decay Poiseuille Flow

We report the results on the orientational dynamics and instabilities in nematic liquid crystal MBBA induced by decaying Poiseuille flow. The experiments were carried out in the rectangular wedge-shape LC cell with thickness varying perpendicular to the flow direction and the confining plates provided homeotropic alignment of a nematic liquid crystal. Increasing the values of initial pressure difference the orientational instability corresponding to the escape of the director out of the shear plane was observed for the first time. This “out-of-plane” transition takes place at some critical pressure difference ΔPc which depends on the local thickness of NLC layer. The results of numerical simulations of governing nematodynamic equations are in a good agreement with experimental data on the threshold of “out-of-plane” instability.

Transient Stripe Patterns of Nematics in a Continuously Rotating Magnetic Field

We investigate periodically amplified transient stripe textures which are spontaneously formed in the asynchronous reorientation regime of a thin homeotropic NLC layer exposed to an in-plane continuously rotating magnetic field. Wavelengths, orientations and ranges of existence of the stripe texture are determined by means of polarizing microscopy. A theoretical model is given which incorporates backflow coupling and stochastic noise. The model eluciates the hydrodynamic pattern formation mechanism and describes the time-periodic characteristics of the structures in good agreement with the experiment.

Anomalous relaxation of a twisted cell under an external magnetic field: The nearly homogeneous relaxation

Abstract We report experimental and theoretical investigations of the dynamic behaviour of a π/2 twisted NLC layer in a magnetic field. When a magnetic field H is applied in the layer plane at a suitable angle β with respect to the easy axis on the first surface, the relaxation towards the equilibrium texture occurs through a slow decay of unstable textures. Depending on the values of H and β, the relaxation of the system can be nearly homogeneous or strongly inhomogeneous. In this paper we restrict our attention to the case where the relaxation occurs in a nearly homogeneous way. The theoretical relaxation time τw of the unstable textures is found to depend strongly on the angle β and on the amplitude of the magnetic field. The experimental dependence of τw on H and β is found to be in good agreement with the theoretical predictions. The relaxation process is extremely sensitive to small dishomogeneities of the director easy alignment on the surfaces. From the measured relaxation we are able to estimate ...

Pattern Formation in a Twisted Nematic Liquid Crystal Cell under an External Magnetic Field

We analyze the spatially inhomogeneous dynamic behaviour of a +~/2 twisted NLC layer in a magnetic field. When a magnetic field H is applied in the layer plane at a suitable angle fl with respect to the easy axis on the first surface, the relaxation toward the equilibrium texture occurs through a slow decay of unstable textures. For some values of fl and H, the relaxation of the unstable texture is strongly inhomogeneous and spatial domains occur everywhere. In this special case, a very rich dynamical behaviour is observed together with the appearance of domains corresponding to unstable, metastable, and stable textures coupled with line defects and walls. We have studied and modelled the form and the properties of the different domains and interfaces, the velocities of the defect lines and the inhomogeneous-homogeneous character of the unstable texture relaxation. The static and dynamic features of the observed domains are in satisfactory agreement with the theoretical predictions.

Noctilucent clouds and regions with polar mesospheric summer echoes studied by means of rocket‐borne electron and ion DC‐probes

During the Noctilucent Cloud Campaign from Esrange, Kiruna, Sweden in July‐August 1991, detailed in situ mesurements were performed by means of plasma probes in the TURBO rocket payload. When launched through NLC and PMSE layers, these probes indicate that the NLC layer was associated with a one kilometer thick region containing heavy positive ions. Embedded in this layer were structures only a few tens of metres in vertical extent. These structures exhibited strongly enhanced ion current and corresponding sharp decreases of electron current. The observations indicate that the structures contain enhanced densities of light positive ions as well as heavy, negative charge carriers in the form of ions or particles. VHF radar measurements from the same site showed Polar Summer Mesospheric Echoes from a layer that at first was located just above the NLC layer, but the rocket results indicate that it later merged with the NLC‐layer.

Investigation of NLC Director Orientational Deformations in Electric Field for Different Boundary Conditions

Abstract The work investigates certain director orientational deformations and the corresponding NLC optical characteristics in electric field for different boundary conditions and consists of two Parts. In Part I we study the effect of Total Internal Reflection (TIR) in NLC layer with homeotropic ( B -effect) or planar ( S-effect) initial orientation subjected to an external electric field. Strong anchoring of the NLC molecules with the substrates is assumed. The intensity of the transmitted light vs angle of incidence is shown to exhibit very sharp and deep oscillations in the vicinity of the TIR angle, the period and the amplitude of the oscillations depending on the applied voltage. The calculated TIR values in B- and S-effects agree with our experimental data. In Part II we investigate orientational deformations of homeotropically aligned NLC layer in an electric field parallel and perpendicular to the initial director orientation ( B-effect and flexoeffect respectively). The apparent strong anchoring of the NLC molecules with the substrates in B-effect, found in our experiment, is explained by introducing the surface energy coupling in the new form.

ALIGNMENT OF NEMATIC LIQUID CRYSTALS CONTROLLED BY FERROELECTRIC DOMAIN STRUCTURE

On cleaved surface of ferroelectric triglycine sulphate (TGS) two distinct alignments of nematic liquid crystals (NLC's) have been observed which correspond to two possible directions of spontaneous polarization in TGS substrate. Polarization reversal of TGS accomplished by external electric field brings about switching from one alignment into the other which remains stable after disconnecting the field. The alignment can be modified by anchoring properties of a glass plate covering the NLC layer.