Microsized Liquid Crystal Research Articles

Electrically driven kinklike distorting waves in microsized liquid crystals.

Electrically driven kinklike distortion regimes in a microsized liquid crystal channel have been investigated both experimentally and analytically. Kinklike distortion waves were excited by the interaction between the electric field E and the gradient ∇n[over ̂] of the director field in a homogeneously aligned liquid crystal (HALC) channel. Having obtained the evolution of the normalized light intensity, which was recorded by the high-speed camera, the process of excitation and evolution of the traveling wave in the HALC channel was visualized for the first time. It was shown, based on a nonlinear extension of the classical Ericksen-Leslie theory, that in the case when the electric field E≫E_{th}, the flow of liquid crystal material completely stops and a new mechanism for converting the electric field arises in the form of the electrically driven distorting traveling kinklike wave, which can be excited in the LC channel, composed of 4-n-pentyl-4^{'}-cyanobiphenyl molecules.

Heat-driven vortical flow in microsized liquid crystal film

ABSTRACTThe theoretical description of vortex dynamics in a hybrid aligned nematic (HAN) microvolume with an orientational defect excited by a temperature gradient, ∇T, is given based on the appropriate nonlinear extension of the classical Ericksen–Leslie theory. We have carried out a numerical study of the system of hydrodynamic equations including director reorientation, fluid flow v and the temperature redistribution across the HAN microvolume under the influence of ∇T, when the HAN microvolume is heated from above. Calculations show that, due to the interaction between the gradient of the director field ∇nˆ and ∇T, the HAN microvolume settles down to a stationary complex-vortex flow regime.PACS numbers: 61.30.Cz, 65.40.De

Thermally excited vortical flow in a microsized liquid crystal volume

The thermally excited vortical flow in a microsized liquid crystal (LC) volume has been investigated theoretically based on the nonlinear extension of the Ericksen-Leslie theory, with accounting the entropy balance equation. Analysis of the numerical results show that due to interaction between the gradients of the director field ∇nˆ and temperature ∇T, caused by the focused laser radiation, the thermally excited vortical fluid flow is maintained in the vicinity of the heat source. Calculations have shown that the features of the vortex flow is influenced not only by the power of the laser radiation, but also by duration of the energy injection into the microsized LC volume.

Hydrodynamic Flows in Microsized Liquid Crystal Cells with Orientational Defects

The effect of the orientational defect (OD) on the formation process of a vortical flow v(t, r), emerging in a microsized liquid crystal (LC) cell under the action of a focused laser radiation, was studied within the nonlinear generalization of the classical Ericksen–Leslie theory by numerical methods, considering the thermomechanical contributions to both the stress tensor and viscous torque, that acts on the unit volume of the liquid crystal phase (LC phase). The analysis of the obtained results showed that the vortical flow, rotating clockwise, is generated in a “defect” LC cell close to the OD, with the OD, placed on the lower bounding surface, on which the laser radiation was focused. The rotational velocity of this flow is two orders of magnitude greater than the rotational velocity of the vortex, which is generated in a “pure” LC cell at the same conditions and rotates anticlockwise.

Гидродинамические течения в микроразмерных жидкокристаллических ячейках с ориентационными дефектами

AbstractThe effect of the orientational defect (OD) on the formation process of a vortical flow v ( t , r ), emerging in a microsized liquid crystal (LC) cell under the action of a focused laser radiation, was studied within the nonlinear generalization of the classical Ericksen–Leslie theory by numerical methods, considering the thermomechanical contributions to both the stress tensor and viscous torque, that acts on the unit volume of the liquid crystal phase (LC phase). The analysis of the obtained results showed that the vortical flow, rotating clockwise, is generated in a “defect” LC cell close to the OD, with the OD, placed on the lower bounding surface, on which the laser radiation was focused. The rotational velocity of this flow is two orders of magnitude greater than the rotational velocity of the vortex, which is generated in a “pure” LC cell at the same conditions and rotates anticlockwise.

Laser-excited motion of liquid crystals confined in a microsized volume with a free surface.

The thermally excited vortical flow in a microsized liquid crystal (LC) volume with a free LC-air interface has been investigated theoretically based on the nonlinear extension of the Ericksen-Leslie theory, with accounting the entropy balance equation. Analysis of the numerical results show that due to interaction between the gradients of the director field ∇n[over ̂] and temperature field ∇T, caused by the focused heating, the thermally excited vortical fluid flow is maintained in the vicinity of the heat source. Calculations show that the magnitude and direction of the velocity field v, as well as the height of the LC-air interface are influenced by the depth of the heat penetration in the LC volume. It has been shown that there is the point in the vicinity of the LC-air interface where the thermally excited vortical flow changes the direction from anticlockwise to clockwise.

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.

Temperature-driven motion of liquid crystals confined in a microvolume

The theoretical description of the reorientational dynamics in microsized liquid crystal (LC) cell, where the nematic sample is confined by two horizontal and two lateral surfaces, under the influence of a temperature gradient ∇T, caused by a laser beam focused on the bounding surface with and without the orientational defect, whereas the rest of the bounding surfaces of the LC cell are kept at constant temperature, has been presented. Our calculations, based on the appropriate nonlinear extension of the classical Ericksen-Leslie theory, show that due to interaction between ∇T and the gradient of the director field \documentclass[12pt]{minimal}\begin{document}$\nabla \hat{{\hbox{\bf n}}}$\end{document}∇n̂ in the LC sample, a thermally excited vortical fluid flow is maintained in the vicinity of the orientational defect, with the motion in the positive sense (clockwise) around the middle part of that defect. In the case of the same LC cell, but without the orientational defect on the lower hotter boundary, the heating regime can also produce the vortical flow in the vicinity of the lower boundary, but with the motion in the negative sense (anti-clockwise) around the middle part of that boundary. At that, the second vortex is characterized by a much slower speed than the vortical flow in the first case.

Polymer-Dispersed Liquid Crystals: Progress in Preparation, Investigation, and Application

Polymer-dispersed liquid crystals (PDLCs), composed of micro-sized liquid crystal domains embedded in a continuous polymer matrix, are an important class of materials that hold promise for many opto-electronic applications. In this review, based on an analysis of research publications appearing between 2006 and 2012, preparation of conventional PDLCs and nanoparticles-doped PDLCs, their properties, and their application for opto-electronic devices are described.

Thermally excited vortical flow in a microsized liquid crystal film

The theoretical description of the reorientational dynamics in a thin bidirectionally aligned liquid crystal (BALC) cell, where the nematic sample is confined by two horizontal and two lateral surfaces, under the influence of the temperature gradient ∇T is presented. We have carried out a numerical study of the system of hydrodynamic equations including director reorientation, fluid flow v, and the temperature redistribution across the BALC cell under the influence of ∇T, when the sample is heated both from below and from above. Calculations show that, due to interaction between the gradient of the director field ∇n and ∇T, the BALC sample settles down to a stationary bi-vortical flow regime. As for a nematogenic material, we have considered the BALC cell to be occupied by 4-n-pentyl-4′-cyanobiphenyl, and investigated the effect of both ∇n and ∇T on the magnitude and direction of v, for a number of hydrodynamic regimes.

A Novel Electrically Tunable Long-Period Fiber Grating Using a Liquid Crystal Cladding Layer

The main aim of the presented work is the integration of a long-period fiber grating and a liquid crystal into a hybrid structure, in order to develop an innovative fiber optic device controlled by an external electric field. The studied long-period fiber grating was fabricated using UV irradiation in a boron co-doped fiber (PS1250/ 1500, manufactured by Fibercore). As a liquid crystal we used a typical 5CB nematic liquid crystal. The sensing mechanism of the proposed loss filter relies on long-period fiber grating attenuation bands sensitivity to optical properties of the liquid crystal layer. The results obtained show that the long-period fiber grating with a nanosized liquid crystal layer exhibits one order of magnitude higher electrical sensitivity and a lower level of the voltage control than the long-period fiber grating with a micro-sized liquid crystal layer. PACS numbers: 42.81.Cn, 42.79.Dj, 42.81.Pa, 42.79.Kr

Electrically and thermally modulated optical properties of polymer dispersed chiral liquid crystal

The polymer dispersed chiral liquid crystals (PDCLCs) film was fabricated by photopolymerization induced phase separation (PIPS) of chiral liquid crystal (CLC)/polymerizable monomers/photoinitiator composites. The effects of the electrical and thermal modulation on optical rotation properties of PDCLCs film were investigated. The microsized liquid crystal droplets were resulted from the rapid polymerization of trifunctional monomers. The effects of the electrically and thermally modulated on realignment of liquid crystal director were investigated. It was found that the intensity of electric and thermal field influenced the alignment of liquid crystal droplets' director on PDCLCs film, and the electro-optical properties of the composites were affected accordingly. The principle of free energy minimum was used for explaining the change of optical rotation and transmittance of PDCLCs film with applying the voltage to the film. The dispersion and sizes of liquid crystal droplets were described by polarizing optical microscope (POM). POLYM. COMPOS., 31:1535–1540, 2010. © 2009 Society of Plastics Engineers