TRICRITICAL POINT IN ORDER-DISORDER PHASE TRANSITIONS FOR NEMATICS

1992 ◽  
Vol 06 (14) ◽  
pp. 2521-2530 ◽  
Author(s):  
G. BARBERO ◽  
L. R. EVANGELISTA ◽  
A. P. KREKHOV
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Liquid Crystals ◽  
External Field ◽  
Tricritical Point ◽  
Nematic Liquid Crystals ◽  
Complete Analysis ◽  
Disorder Phase Transition ◽  
Anchoring Strength ◽  
Strong Anchoring

A complete analysis of the order-disorder phase transition in nematic liquid crystals induced by an external field is presented. The case of nearly compensated nematics in weak anchoring situation is discussed. The investigation shows that the parameter controlling the order of the phase transition is a decreasing function of the anchoring strength. The important limiting cases of very weak and very strong anchoring are considered too.

scholarly journals Gradient theory of domain walls in thin, nematic liquid crystals films

2019 ◽  
Vol 22 (07) ◽  
pp. 1950063
Author(s):  
Marcel G. Clerc ◽  
Michał Kowalczyk ◽  
Panayotis Smyrnelis
Keyword(s):  
Phase Transition ◽  
Liquid Crystal ◽  
Liquid Crystals ◽  
External Field ◽  
Nematic Liquid Crystal ◽  
Domain Walls ◽  
Nematic Liquid Crystals ◽  
Gradient Theory ◽  
Crystal Sample ◽  
Bistable Region

In this paper, we describe domain walls appearing in a thin, nematic liquid crystal sample subject to an external field with intensity close to the Fréedericksz transition threshold. Using the gradient theory of the phase transition adapted to this situation, we show that depending on the parameters of the system, domain walls occur in the bistable region or at the border between the bistable and the monostable region.

FREEDERICKSZ-LIKE TRANSITIONS IN COMPENSATED NEMATIC LIQUID CRYSTALS

1991 ◽  
Vol 05 (04) ◽  
pp. 697-707
Author(s):  
G. BARBERO ◽  
L.R. EVANGELISTA ◽  
Z. GABBASOVA
Keyword(s):  
Phase Transition ◽  
Phase Diagram ◽  
Liquid Crystals ◽  
Relative Phase ◽  
Nematic Liquid Crystals ◽  
Dielectric Anisotropy ◽  
Critical Fields ◽  
Inversion Point ◽  
Disorder Phase Transition ◽  
First Order

The occurrence of the Freedericksz transitions at the inversion point of the main dielectric anisotropy in nematic liquid crystals is discussed. It is shown that, if this kind of order-disorder phase transition can take place, they are always of the first order. The critical fields are evaluated, and the relative phase diagram is discussed.

scholarly journals Expulsion of disclinations in nematic liquid crystals

2003 ◽  
Vol 14 (1) ◽  
pp. 39-59 ◽  
Author(s):  
PAOLO BISCARI ◽  
TIMOTHY J. SLUCKIN
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Boundary Conditions ◽  
Half Space ◽  
Nematic Liquid Crystal ◽  
Nematic Liquid Crystals ◽  
Critical Value ◽  
Repulsive Force ◽  
Anchoring Strength ◽  
Strong Anchoring

We study the interactions between a nematic liquid crystal disclination and the surface of the half-space which bounds it. When strong anchoring conditions are applied on the boundary, the biaxial core of the disclination affects the repulsive force that tends to drive the disclination away from the surface. If we replace the strong boundary conditions with an anchoring potential, the surface-disclination interaction depends on the surface extrapolation length. In particular, the nematic may expel the disclination if the anchoring strength is below a critical value.

scholarly journals Emergence and stabilization of transient twisted defect structures in confined achiral liquid crystals at a phase transition.

Soft Matter ◽  
2021 ◽  
Author(s):  
Jose X Velez ◽  
Zhaofei Zheng ◽  
Daniel A. Beller ◽  
Francesca Serra
Keyword(s):  
Phase Transition ◽  
Liquid Crystals ◽  
Soft Matter ◽  
Capillary Tube ◽  
Nematic Liquid Crystals ◽  
Defect Structures

Spontaneous emergence of chirality is a pervasive theme in soft matter. We report a transient twist forming in achiral nematic liquid crystals confined to a capillary tube with square cross...

Molecular Ordering in Nematic MBCA and EPAPU

1990 ◽  
Vol 45 (1) ◽  
pp. 29-32
Author(s):  
S. Sreehari Sastry ◽  
V. Venkata Rao ◽  
P. Narayana Murty ◽  
G. Satyanandam ◽  
T. F. Sundar Raj
Keyword(s):  
Phase Transition ◽  
Liquid Crystals ◽  
Order Parameter ◽  
Nematic Phase ◽  
Spin Probe ◽  
Nematic Liquid Crystals ◽  
Experimental Techniques ◽  
First Order ◽  
Molecular Ordering

AbstractBy EPR, two nematic liquid crystals (MBCA and EPAPU) were investigated using a steroidal nitroxide spin probe. In both liquid crystals the isotropic-nematic phase transition is of first order. The observed variation of the order parameter with temperature is compared with predictions from the Maier-Saupe and Humphries-James-Luckhurst models and with results obtained by several other experimental techniques.

scholarly journals Phase transitions and critical phenomena of ice under high pressure

2014 ◽  
Vol 70 (a1) ◽  
pp. C894-C894
Author(s):  
Masakazu Matsumoto ◽  
Kazuhiro Himoto ◽  
Kenji Mochizuki ◽  
Hideki Tanaka
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Phase Transitions ◽  
Phase Boundary ◽  
Liquid Water ◽  
Tricritical Point ◽  
Melting Curve ◽  
Md Simulations ◽  
Free Energy Calculations ◽  
Lattice Points

Water distributes ubiquitously among the solar system and outer space in a wide variety of solid forms, i.e. more than ten kinds of crystalline ice, two types of amorphous ice, and clathrate hydrates. These polymorphs often play crucial roles in the planetary geology. Diversity of the stable ices and hydrates also suggests the existence of the various kinds of stable and metastable phases yet to be discovered [1]. Computer simulations and the theoretical treatments are useful to explore them. In this talk, we introduce the phase transitions of ice VII, which is one of the highest-pressure ice phases. The melting curve of ice VII to high-pressure liquid water has not been settled by experiments. We have proposed the intervention of a plastic phase of ice (plastic ice) between ice VII and liquid water, based on molecular dynamics (MD) simulations and the free energy calculations [2], which enables to account for large gaps among the various experimental curves of ice VII. In plastic ice, the water molecules are fixed at the lattice points, while they rotate freely. Interestingly, our additional survey by large-scale MD simulations elucidates that the phase transition between ice VII and plastic ice is first-order at low pressure as it was already predicted, while it is found to be second-order at higher pressures, where a tricritical point joins these phase boundaries together [3]. The critical fluctuations may give a clue for determining the phase boundary experimentally. We also argue about the phase transition dynamics of liquid water to ice VII at their direct phase boundary where metastable plastic ice phase plays an important role.

Ultra-fast Time-Resolved Electron Diffraction of Strongly Driven Phase Transitions on Silicon Surfaces

2009 ◽  
Vol 1230 ◽  
Author(s):  
Simone Möllenbeck ◽  
Anja Hanisch-Blicharski ◽  
Paul Schneider ◽  
Manuel Ligges ◽  
Ping Zhou ◽  
...  
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Electron Diffraction ◽  
Structural Phase ◽  
High Energy ◽  
Silicon Surfaces ◽  
Fast Time ◽  
Time Resolved ◽  
Disorder Phase Transition ◽  
Pulse Pump

AbstractThe dynamics of strongly driven phase transitions at surfaces are studied by ultra-fast time-resolved reflection high energy electron diffraction. The surfaces are excited by an intense fs-laser pulse (pump) and probed by an ultra-short electron pulse with variable time delay. The order-disorder phase transition from a c(4×2) to a (2×1) of the bare Si(001) surface shows a transient decrease of the intensity of the c(4×2) spots which recovers on a time scale of a few hundred picoseconds indicating the excitation of the phase transition. On Si(111) a monolayer of Indium induces a (4×1) reconstruction which undergoes a Peierls like phase transition to a (8ד2”) reconstruction below 100 K. Upon laser excitation at a temperature of 40 K the phase transition was strongly driven. The (8ד2”)-diffraction spots instantaneously disappears, while the intensity of the (4×1)-spots increases. This increase of the (4×1) spot intensity excludes an explanation by the Debye-Waller-Effect and is evidence for a true structural phase transition at a surface.

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