Electric and Magnetic Field Investigations of the Periodic Gridlike Deformation of a Cholesteric Liquid Crystal

1972 ◽  
Vol 28 (10) ◽  
pp. 593-596 ◽  
Author(s):  
T. J. Scheffer
Keyword(s):  
Magnetic Field ◽  
Liquid Crystal ◽  
Cholesteric Liquid Crystal ◽  
Field Investigations ◽  
Electric And Magnetic Field

Magnetic‐Field Effects on a Compensated Cholesteric Liquid Crystal

1969 ◽  
Vol 51 (10) ◽  
pp. 4186-4188 ◽  
Author(s):  
Thomas M. Laronge ◽  
H. Baessler ◽  
M. M. Labes
Keyword(s):  
Magnetic Field ◽  
Liquid Crystal ◽  
Cholesteric Liquid Crystal ◽  
Magnetic Field Effects ◽  
Field Effects

Effect of static magnetic field on the helical flow of incompressible cholesteric liquid crystal between two coxial circular cylinders having rotational and axial velocities

1976 ◽  
Vol 19 (3) ◽  
pp. 371-380
Author(s):  
G. Paria ◽  
A. K. Sharma
Keyword(s):  
Magnetic Field ◽  
Liquid Crystal ◽  
Angular Velocity ◽  
Static Magnetic Field ◽  
Axial Velocity ◽  
Cholesteric Liquid Crystal ◽  
Helical Flow ◽  
Circular Cylinders ◽  
The Magnetic Field ◽  
Orientation Of Molecules

AbstractThe paper investigates the effect of a static magnetic field on the helical flow of an incompressible cholestenc liquid crystal with director of unit magnitude between two coaxial circular cylinders rotating with different angular velocities about their common axis and moving with different axial velocities. At low shear rates with a weak magnetic field in the axial direction, the axial velocity, the angular velocity and the orientation of molecules between the two cylinders have been obtained. It is found that the magnetic field has influenced the orientation of molecules while the axial velocity and the angular velocity remain uneffected by the magnetic field.

Uniqueness of director configuration states for liquid crystals in the case of weak anchoring

2019 ◽  
Vol 84 (4) ◽  
pp. 748-762
Author(s):  
Carlo Greco
Keyword(s):  
Magnetic Field ◽  
Liquid Crystal ◽  
External Field ◽  
Thin Layer ◽  
Elastic Constants ◽  
Cholesteric Liquid Crystal ◽  
Stable Configuration ◽  
Director Field ◽  
Critical Thresholds ◽  
Bounding Surfaces

Abstract In a thin layer of liquid crystal the configuration of the director field depends on the interaction between the elastic properties of the material, the thickness $d$ of the layer, the boundary conditions and the external fields that may have been applied. Suitable combinations of these factors can give rise to distorted configurations (Freedericksz transitions). In this paper we assume the Oseen-Frank model for the energy and that the director field depends only on the direction orthogonal to the layer; we assume also weak anchoring conditions at the two bounding surfaces, and we mainly study the problem of uniqueness of such distorted configurations. More precisely, we first consider the nematic case in the presence of a magnetic field $\mathbf H$, and we prove the uniqueness of the stable configuration provided the magnitude of $\mathbf H$ is between two critical thresholds, simplifying some results already known in the literature, and calculating explicitly the critical thresholds. Then we study the case of a cholesteric liquid crystal without external field. In this case the director field tends to form a right-angle helicoid around a twist axis orthogonal to the layer, and we have distorted configurations (namely oblique helicoid) for suitable value of $d$. Also in this case, with suitable restrictions on the elastic constants in the Oseen-Frank energy, we find two critical thresholds for $d$, and we prove the existence of only one stable director configuration if $d$ is between them.

Cholesteric pitch-transitions induced by a magnetic field in a sample containing incomplete number of pitches

Open Physics ◽  
2012 ◽  
Vol 10 (3) ◽  
Author(s):  
Ioannis Lelidis ◽  
Giovanni Barbero ◽  
Antonio Scarfone
Keyword(s):  
Magnetic Field ◽  
Liquid Crystal ◽  
Boundary Conditions ◽  
Elastic Energy ◽  
Twist Angle ◽  
Cholesteric Liquid Crystal ◽  
Finite Thickness ◽  
Helical Axis ◽  
Rigid Boundary

AbstractWe investigate the pitch transitions induced by an external bulk field in a Cholesteric Liquid Crystal slab of finite thickness ℓ that contains an incomplete number of π-twists. The analysis is performed for a magnetic field that is (i) perpendicular to the helical axis, and (ii) tilted with respect to one of the easy directions imposed by planar and rigid boundary conditions. For finite ℓ we obtain a cascade of transitions, where the bulk expels a half-pitch at a time with increasing field to avoid divergences in the elastic energy. The dependence of the threshold magnetic field inducing the expulsion on the easy axes twist angle δ is investigated for all the cascade of pitch transitions and in particular for the final one, corresponding to the Cholesteric-Nematic transition. In the ℓ → ∞ limit this dependence disappears and we reobtain the results of de Gennes for an infinite sample.

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