Лазерная нанофлюидика жидких кристаллов

Abstract Several scenarios of formation of hydrodynamic flows in nanoscale planar-oriented liquid-crystal (POLC) channels are described by numerical methods within nonlinear generalization of the classical Ericksen–Leslie theory, which allows for consideration of thermomechanical contributions both to the expression for shear stress and the equation of entropy balance. A vortex flow can eventually be formed in a nanoscale POLC channel as a result of the formation of both temperature gradient ∇ T (in the initially uniformly heated POLC channel under focused laser irradiation) and director field gradient $$\nabla {\mathbf{\hat {n}}}$$ (under a static electric field arising in the natural way at the LC phase/solid interface) and due to the interaction between ∇ T and $$\nabla {\mathbf{\hat {n}}}$$ .

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Сдвиговой режим формирования градиента температуры в тонком нематическом канале

Физика твердого тела ◽

10.21883/ftt.2019.04.47430.305 ◽

2019 ◽

Vol 61 (4) ◽

pp. 779

Author(s):

А.В. Захаров ◽

С.В. Пасечник ◽

Д.В. Шмелева

Keyword(s):

Shear Stress ◽

Liquid Crystal ◽

Numerical Methods ◽

Temperature Gradient ◽

Thermal Insulation ◽

Constant Temperature ◽

Balance Equation ◽

Set Up ◽

Boundary Surfaces ◽

Upper Boundary

AbstractIt has been shown by means of numerical methods, in the framework of the classical Ericksen-Leslie theory, together with accounting the entropy balance equation, how a temperature gradient, in the initially uniformly heated a hybrid-oriented liquid crystal (HOLC) channel, may set up under action of a shear stress (SS). The cases of complete and partial thermal insulation of one of the boundary surfaces of the HOLC are analyzed under the condition that a constant temperature is kept on the rest boundaries. It also has been shown how to heat up the planarly oriented upper boundary of the HOLC channel under the influence of the SS and, thereby, to form the temperature gradient across the HOLC channel.

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Modeling Static Electric Field Effect on Nematic Liquid Crystal Director Orientation in Side-Electrode Cell

EPJ Web of Conferences ◽

10.1051/epjconf/201817303002 ◽

2018 ◽

Vol 173 ◽

pp. 03002 ◽

Cited By ~ 2

Author(s):

Alexander Ayriyan ◽

Edik Ayryan ◽

Alexandre Egorov ◽

Maria Dencheva-Zarkova ◽

Georgi Hadjichristov ◽

...

Keyword(s):

Liquid Crystal ◽

Electric Field ◽

Nematic Liquid Crystal ◽

Finite Difference Methods ◽

Electric Field Effect ◽

Dimensional Model ◽

Static Electric Field ◽

Electrode Cell ◽

Field Influence ◽

Director Orientation

A two-dimensional model of Fredericks effect was used for the investigation of the static electric field influence on nematic liquid crystal director orientation in the side-electrode cell. The solutions of the equations describing the model were obtained by finite-difference methods. Fredericks transition threshold for the central part of the cell, as well as dependencies of the distribution of the director orientation patterns on the electric field and location, were obtained. The numerical results are found to agree qualitatively with the experiment. Further investigations are needed to elucidate completely the Fredericks effect.

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On the Dynamics of the Weak Fréedericksz Transition for Nematic Liquid Crystals

Communications in Computational Physics ◽

10.4208/cicp.190615.090516a ◽

2016 ◽

Vol 20 (5) ◽

pp. 1359-1380 ◽

Cited By ~ 1

Author(s):

Peder Aursand ◽

Gaetano Napoli ◽

Johanna Ridder

Keyword(s):

Liquid Crystal ◽

Finite Difference ◽

Finite Difference Method ◽

Electric Field ◽

Excited States ◽

Difference Method ◽

Static Case ◽

Director Field ◽

Implicit Finite Difference ◽

Anchoring Strength

AbstractWe propose an implicit finite-difference method to study the time evolution of the director field of a nematic liquid crystal under the influence of an electric field with weak anchoring at the boundary. The scheme allows us to study the dynamics of transitions between different director equilibrium states under varying electric field and anchoring strength. In particular, we are able to simulate the transition to excited states of odd parity, which have previously been observed in experiments, but so far only analyzed in the static case.

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The Role of Inertia and Dissipation in the Dynamics of the Director for a Nematic Liquid Crystal Coupled with an Electric Field

Communications in Computational Physics ◽

10.4208/cicp.220414.231214a ◽

2015 ◽

Vol 18 (1) ◽

pp. 147-166 ◽

Cited By ~ 1

Author(s):

Peder Aursand ◽

Johanna Ridder

Keyword(s):

Liquid Crystal ◽

Electric Field ◽

Nematic Liquid Crystal ◽

Relative Strength ◽

Inertial Forces ◽

Director Field ◽

Voltage Difference ◽

Electrostatic Equilibrium ◽

Variational Wave

AbstractWe consider the dynamics of the director in a nematic liquid crystal when under the influence of an applied electric field. Using an energy variational approach we derive a dynamic model for the director including both dissipative and inertial forces.A numerical scheme for the model is proposed by extending a scheme for a related variational wave equation. Numerical experiments are performed studying the realignment of the director field when applying a voltage difference over the liquid crystal cell. In particular, we study how the relative strength of dissipative versus inertial forces influence the time scales of the transition between the initial configuration and the electrostatic equilibrium state.

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Direct laser writing of liquid crystal elastomers oriented by a horizontal electric field

Open Research Europe ◽

10.12688/openreseurope.14135.2 ◽

2021 ◽

Vol 1 ◽

pp. 129

Author(s):

Marco Carlotti ◽

Omar Tricinci ◽

Frank den Hoed ◽

Stefano Palagi ◽

Virgilio Mattoli

Keyword(s):

Liquid Crystal ◽

Electric Field ◽

Microelectromechanical Systems ◽

Functional Materials ◽

Direct Laser Writing ◽

Static Electric Field ◽

Laser Writing ◽

Printing Process ◽

Direct Laser ◽

Liquid Crystal Elastomers

Background: The ability to fabricate components capable of performing actuation in a reliable and controlled manner is one of the main research topics in the field of microelectromechanical systems (MEMS). However, the development of these technologies can be limited in many cases by 2D lithographic techniques employed in the fabrication process. Direct Laser Writing (DLW), a 3D microprinting technique based on two-photon polymerization, can offer novel solutions to prepare, both rapidly and reliably, 3D nano- and microstructures of arbitrary complexity. In addition, the use of functional materials in the printing process can result in the fabrication of smart and responsive devices. Methods: In this study, we present a novel methodology for the printing of 3D actuating microelements comprising Liquid Crystal Elastomers (LCEs) obtained by DLW. The alignment of the mesogens was performed using a static electric field (1.7 V/µm) generated by indium-tin oxide (ITO) electrodes patterned directly on the printing substrates. Results: When exposed to a temperature higher than 50°C, the printed microstructures actuated rapidly and reversibly of about 8% in the direction perpendicular to the director. Conclusions: A novel methodology was developed that allows the printing of directional actuators comprising LCEs via DLW. To impart the necessary alignment of the mesogens, a static electric field was applied before the printing process by making use of flat ITO electrodes present on the printing substrates. The resulting microelements showed a reversible change in shape when heated higher than 50 °C.

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Формирование вихревых течений в жидкокристаллических фазах инкапсулированных в микролитровые объемы под действием сфокусированного лазерного излучения

Физика твердого тела ◽

10.21883/ftt.2018.07.46135.011 ◽

2018 ◽

Vol 60 (7) ◽

pp. 1431

Author(s):

А.В. Захаров

Keyword(s):

Free Surface ◽

Liquid Crystal ◽

Laser Radiation ◽

Unit Volume ◽

Vortex Formation ◽

Theoretical Description ◽

Vortex Flows ◽

Hydrodynamic Modes ◽

Director Field ◽

Nonlinear Generalization

AbstractA theoretical description of the process of formation of vortex flows v ( t , r ) and the evolution of the director field $$\hat n$$ n ^ in microliter liquid crystal (LC) volumes with a free surface under the influence of a temperature gradient ∇ T ( t , r ), which is initiated by focused laser radiation, has been proposed. Thermomechanical contributions to both the stress tensor and viscous moment which are acting per unit volume of the LC phase were taken into account in the framework of the nonlinear generalization of the classical Ericksen−Leslie theory, which allowed describing the origin and formation of vortex flows in nematics formed by 4-n-pentyl- 4'-cyanobiphenyl molecules. Various hydrodynamic modes of vortex formation in microsized LC volumes under the action of focused laser radiation have been investigated by numerical methods.

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Гидродинамические течения в микроразмерных жидкокристаллических ячейках с ориентационными дефектами

Физика твердого тела ◽

10.21883/ftt.2018.09.46407.068 ◽

2018 ◽

Vol 60 (9) ◽

pp. 1834

Author(s):

А.В. Захаров

Keyword(s):

Liquid Crystal ◽

Laser Radiation ◽

Numerical Methods ◽

Unit Volume ◽

Rotational Velocity ◽

Vortical Flow ◽

Liquid Crystal Phase ◽

Lower Bounding ◽

Nonlinear Generalization ◽

Viscous Torque

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.

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