Observation of Magnetic-Field—Induced First-Order Optical Fréedericksz Transition in a Nematic Film

1986 ◽  
Vol 57 (4) ◽  
pp. 448-451 ◽  
Author(s):  
A. J. Karn ◽  
S. M. Arakelian ◽  
Y. R. Shen ◽  
H. L. Ong
Keyword(s):  
Magnetic Field ◽  
Freedericksz Transition ◽  
First Order ◽  
Fréedericksz Transition

scholarly journals Fréedericksz transition in a periodic magnetic field

1988 ◽  
Vol 38 (5) ◽  
pp. 2641-2649 ◽  
Author(s):  
M. C. Torrent ◽  
F. Sagués ◽  
F. Arias ◽  
M. San Miguel
Keyword(s):  
Magnetic Field ◽  
Freedericksz Transition ◽  
Periodic Magnetic Field ◽  
Fréedericksz Transition

Quanta Energy Level Structure and the First-Order Freedericksz Transition of Weak Anchoring NLC Cells

2010 ◽  
Vol 428-429 ◽  
pp. 402-405
Author(s):  
Rong Hua Guan
Keyword(s):  
Liquid Crystal ◽  
Energy Level ◽  
Energy Levels ◽  
Level Structure ◽  
Stable State ◽  
Freedericksz Transition ◽  
Energy Level Structure ◽  
First Order ◽  
Liquid Crystal System ◽  
Fréedericksz Transition

The energy problem of weak anchoring nematic liquid crystal (NLC) cell is investigated. For given system, there are four solutions satisfying mechanical equilibrium conditions simultaneity under certain condition. Liquid crystal system exist quanta energy level. The values and sequence of energy levels related to the change of external field and anchoring parameters. The state with the smallest energy is the stable state and the others are metastable states, which are separated by the energy barriers. The Freedericksz transition can be considered as the director slippage through these barriers to the lowest energy level and the first order transition and bistable state result from the existence of the multiple disturbed solutions.

scholarly journals Bifurcation analysis of the twist-Fréedericksz transition in a nematic liquid-crystal cell with pre-twist boundary conditions

2009 ◽  
Vol 20 (3) ◽  
pp. 269-287 ◽  
Author(s):  
FERNANDO P. DA COSTA ◽  
EUGENE C. GARTLAND ◽  
MICHAEL GRINFELD ◽  
JOÃO T. PINTO
Keyword(s):  
Magnetic Field ◽  
Liquid Crystal ◽  
Boundary Conditions ◽  
Nematic Liquid Crystal ◽  
Pitchfork Bifurcation ◽  
Critical Magnetic Field ◽  
Twist Boundary ◽  
Freedericksz Transition ◽  
Diamagnetic Anisotropy ◽  
Fréedericksz Transition

Motivated by a recent investigation of Millar and McKay [Director orientation of a twisted nematic under the influence of an in-plane magnetic field. Mol. Cryst. Liq. Cryst435, 277/[937]–286/[946] (2005)], we study the magnetic field twist-Fréedericksz transition for a nematic liquid crystal of positive diamagnetic anisotropy with strong anchoring and pre-twist boundary conditions. Despite the pre-twist, the system still possesses ℤ2 symmetry and a symmetry-breaking pitchfork bifurcation, which occurs at a critical magnetic-field strength that, as we prove, is above the threshold for the classical twist-Fréedericksz transition (which has no pre-twist). It was observed numerically by Millar and McKay that this instability occurs precisely at the point at which the ground-state solution loses its monotonicity (with respect to the position coordinate across the cell gap). We explain this surprising observation using a rigorous phase-space analysis.

scholarly journals The Beauty of Twist-Bend Nematic Phase: Fast Switching Domains, First Order Fréedericksz Transition and a Hierarchy of Structures

Crystals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 621
Author(s):  
Vitaly P. Panov ◽  
Jang-Kun Song ◽  
Georg H. Mehl ◽  
Jagdish K. Vij
Keyword(s):  
Nematic Phase ◽  
Liquid Crystalline ◽  
Hierarchical Structures ◽  
Freedericksz Transition ◽  
First Order ◽  
Polymer Templating ◽  
Optical Retardation ◽  
Second Order Transition ◽  
Fréedericksz Transition ◽  
Hierarchy Of Structures

The twist-bend nematic phase (NTB) exhibits a complicated hierarchy of structures responsible for several intriguing properties presented here. These are: the observation of a fast electrooptic response, the exhibition of a large electroclinic effect, and the observation of an unusual pattern of the temperature dependence of birefringence of bent-shaped bimesogens in parallel-rubbed planar-aligned cells. These unusual effects inspired the use of highly sophisticated techniques that led to the discovery of the twist-bend nematic phase. Results of the optical retardation of a parallel-rubbed planar-aligned cell show that the ‘heliconical angle’ (the angle the local director makes with the optical axis) starts increasing in the high temperature N phase, it exhibits a jump at the N–NTB transition temperature and continues to increase in magnitude with a further reduction in temperature. The liquid crystalline parallel-rubbed planar-aligned and twist-aligned cells in this phase exhibit fascinating phenomena such as a demonstration of the beautiful stripes and dependence of their periodicity on temperature. The Fréedericksz transition in the NTB phase is found to be of the first order both in rubbed planar and homeotropic-aligned cells, in contrast to the second order transition exhibited by a conventional nematic phase. This transition shows a significant hysteresis as well as an abrupt change in the orientation of the director as a function of the applied electric field. Hierarchical structures are revealed using the technique of polymer templating the structure of the liquid crystalline phase of interest, and imaging of the resulting structure by scanning electron microscopy.

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