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

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.

Download Full-text

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.

Download Full-text

Лазерная нанофлюидика жидких кристаллов

Физика твердого тела ◽

10.21883/ftt.2020.06.49359.002 ◽

2020 ◽

Vol 62 (6) ◽

pp. 965

Author(s):

Izabela Sliwa ◽

А.В. Захаров

Keyword(s):

Shear Stress ◽

Liquid Crystal ◽

Numerical Methods ◽

Temperature Gradient ◽

Electric Field ◽

Vortex Flow ◽

Static Electric Field ◽

Director Field ◽

Nonlinear Generalization ◽

Natural Way

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 $$\nabla {\mathbf{\hat {n}}}$$ .

Download Full-text

Термомеханический режим формирования вихревых течений в гибридно ориентированном нематическом канале

Физика твердого тела ◽

10.21883/ftt.2019.06.47699.358 ◽

2019 ◽

Vol 61 (6) ◽

pp. 1197

Author(s):

А.В. Захаров

Keyword(s):

Shear Stress ◽

Liquid Crystal ◽

Balance Equation ◽

Numerical Results ◽

Vortical Flow ◽

Vortex Flows ◽

Entropy Balance ◽

Initial Stage ◽

Nonlinear Generalization

AbstractIn this paper, we described numerically several scenarios of formation of vortex flows (VF) in microsized hybrid-oriented liquid crystal (HOLC) channels with orientation defects using a nonlinear generalization of the classical Ericksen–Leslie theory that allows taking into account termomechanical contribution, both in the expression for the shear stress and in the entropy balance equation. An analysis of the numerical results showed that there are two or one vortices in the HOLC channel although two vortices directed towards each other are generated at the initial stage of the VT formation Thermomechanically Excited Vortical Flow.

Download Full-text

Динамика деформации нематика под действием сильных скрещенных электрического и магнитного полей

Физика твердого тела ◽

10.21883/ftt.2018.03.45568.246 ◽

2018 ◽

Vol 60 (3) ◽

pp. 603

Author(s):

А.В. Захаров

Keyword(s):

Liquid Crystal ◽

Nematic Liquid Crystal ◽

Unit Volume ◽

Periodic Structures ◽

Numerical Calculations ◽

Director Field ◽

Rectangular Cell ◽

Rotational Viscosity ◽

Reorientation Time

AbstractA new mode of reorientation of the field of director $$\hat n$$ n ^ of a nematic liquid crystal (LC) encapsulated into a rectangular cell under strong crossed electric ( E ) and magnetic ( B ) fields has been proposed. Numerical calculations performed within the linear generalization of the classical Ericksen–Leslie theory show that transition periodic structures facilitating a decrease in the effective rotational viscosity of a nematic, formed by 4- n -pentyl-4'-cyanobiphenyl (5CB) molecules, may arise during reorientation of $$\hat n$$ n ^ at certain ratios of the moments and momenta per unit volume of the LC phase and when E ≫ E _th. The calculations conducted for 5CB also indicate that the periodic structures formed in a LC cell facilitate a decrease in reorientation time τ_on of the director field.

Download Full-text

Formation of Vortex Flows in Liquid Crystal Phases Encapsulated in Microliter Volumes under the Action of Focused Laser Radiation

Physics of the Solid State ◽

10.1134/s1063783418070326 ◽

2018 ◽

Vol 60 (7) ◽

pp. 1447-1457

Author(s):

A. V. Zakharov

Keyword(s):

Liquid Crystal ◽

Laser Radiation ◽

Vortex Flows ◽

Crystal Phases ◽

Liquid Crystal Phases

Download Full-text

Elastocapillary interactions on nematic films

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1504817112 ◽

2015 ◽

Vol 112 (20) ◽

pp. 6336-6340 ◽

Cited By ~ 16

Author(s):

Iris B. Liu ◽

Mohamed A. Gharbi ◽

Victor L. Ngo ◽

Randall D. Kamien ◽

Shu Yang ◽

...

Keyword(s):

Surface Tension ◽

Free Surface ◽

Liquid Crystal ◽

Easy Axis ◽

Particle Migration ◽

Fluid Interfaces ◽

Particle Assembly ◽

Director Field ◽

Liquid Crystal Films ◽

Crystal Films

Rod-like colloids distort fluid interfaces and interact by capillarity. We explore this interaction at the free surface of aligned nematic liquid crystal films. Naive comparison of capillary and elastic energies suggests that particle assembly would be determined solely by surface tension. Here, we demonstrate that, under certain circumstances, the capillary and elastic effects are complementary and each plays an important role. Particles assemble end-to-end, as dictated by capillarity, and align along the easy axis of the director field, as dictated by elasticity. On curved fluid interfaces, however, curvature capillary energies can overcome the elastic orientations and drive particle migration along curvature gradients. Domains of dominant interaction and their transition are investigated.

Download Full-text