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 Order Parameters, Orientational Distribution Functions and Heliconical Tilt Angles of Oligomeric Liquid Crystals

2019 ◽  
Author(s):  
Richard Mandle ◽  
John W. Goodby
Keyword(s):  
Phase Transition ◽  
Liquid Crystals ◽  
Tilt Angle ◽  
Order Parameter ◽  
Nematic Phase ◽  
Liquid Crystalline ◽  
Thermal Evolution ◽  
Order Parameters ◽  
Distribution Functions ◽  
Orientational Distribution

We compare the order parameters, orientational distribution functions (ODF) and heliconical tilt angles of the TB phase exhibited by a liquid-crystalline dimer (CB7CB) to a tetramer (O47) and hexamer (O67) by SAXS/WAXS. Following the N-TB phase transition we find that all order parameters decrease, and while 〈P2 〉 remains positive 〈P4 〉 becomes negative. For all three materials the order parameter 〈P6 〉 is near zero in both phases. The ODF is sugarloaf-like in the nematic phase and volcano-like in the TB phase, allowing us to estimate the heliconical tilt angle of each material and its thermal evolution. The heliconical tilt angle appears to be largely independent of the material studied despite the differing number of mesogenic units.

ESR Study of Molecular Ordering in PEBAB and PMBAB

1984 ◽  
Vol 39 (7) ◽  
pp. 700-702 ◽  
Author(s):  
N. V. S. Rao ◽  
V. G. K. M. Pisipati ◽  
P. V. Datta Prasad ◽  
D. Saran
Keyword(s):  
Liquid Crystals ◽  
Order Parameter ◽  
Close Agreement ◽  
Nematic Liquid Crystals ◽  
Nitroxide Radical ◽  
Molecular Ordering ◽  
Paramagnetic Probe

An ESR study of the nematic liquid crystals PEBAB and PMBAB has been carried out using a nitroxide radical as paramagnetic probe. The order parameter (5) determined this way are in close agreement with those determined by NMR. For EBAB our S values differ from those determined by ESR with a different probe (VAAC).

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 Notizen: Specific Volume Studies on Some Nematic Liquid Crystals

1975 ◽  
Vol 30 (8) ◽  
pp. 1094-1096 ◽  
Author(s):  
Birendra Bahadur
Keyword(s):  
Phase Transition ◽  
Liquid Crystals ◽  
Order Phase Transition ◽  
Specific Volume ◽  
Nematic Liquid Crystals ◽  
Adiabatic Compressibility ◽  
First Order ◽  
First Order Phase Transition ◽  
First Order Phase ◽  
Sudden Jump

Abstract The temperature variation of the specific volume of two nematic liquid crystals (HBT and OBT) has been observed in both the nematic and isotropic regions. A sudden jump is observed in the vicinity of the nematic-isotropic transition indicating a first order phase transition. Pretransitional effects are found to occur only on the nematic side of the transition. This accords with the Maier-Saupe theory. Some parameters such as SK , A, the adiabatic compressibility, the Rao number, and the van der Waals constant are also determined.

scholarly journals Order Parameters, Orientational Distribution Functions and Heliconical Tilt Angles of Oligomeric Liquid Crystals

2019 ◽  
Author(s):  
Richard Mandle ◽  
John W. Goodby
Keyword(s):  
Phase Transition ◽  
Liquid Crystals ◽  
Tilt Angle ◽  
Order Parameter ◽  
Nematic Phase ◽  
Liquid Crystalline ◽  
Thermal Evolution ◽  
Order Parameters ◽  
Distribution Functions ◽  
Orientational Distribution

We compare the order parameters, orientational distribution functions (ODF) and heliconical tilt angles of the TB phase exhibited by a liquid-crystalline dimer (CB7CB) to a tetramer (O47) and hexamer (O67) by SAXS/WAXS. Following the N-TB phase transition we find that all order parameters decrease, and while 〈P2 〉 remains positive 〈P4 〉 becomes negative. For all three materials the order parameter 〈P6 〉 is near zero in both phases. The ODF is sugarloaf-like in the nematic phase and volcano-like in the TB phase, allowing us to estimate the heliconical tilt angle of each material and its thermal evolution. The heliconical tilt angle appears to be largely independent of the material studied despite the differing number of mesogenic units.

scholarly journals Phase transitions in nematics: textures with tactoids and disclinations

2020 ◽  
Vol 15 ◽  
pp. 8 ◽  
Author(s):  
Dmitry Golovaty ◽  
Young-Ki Kim ◽  
Oleg D. Lavrentovich ◽  
Michael Novack ◽  
Peter Sternberg
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Liquid Crystals ◽  
Numerical Simulations ◽  
Elastic Constants ◽  
Nematic Phase ◽  
Topological Defects ◽  
First Order ◽  
Gennes Theory

We demonstrate that a first order isotropic-to-nematic phase transition in liquid crystals can be succesfully modeled within the generalized Landau-de Gennes theory by selecting an appropriate combination of elastic constants. The numerical simulations of the model established in this paper qualitatively reproduce the experimentally observed configurations that include interfaces and topological defects in the nematic phase.

scholarly journals Static and Dynamic Properties of Ferroelectric Liquid Crystals in the Vicinity of a First-Order SmA-SmC* Phase Transition

1992 ◽  
Vol 47 (3) ◽  
pp. 536-542 ◽  
Author(s):  
Roland R. Netz ◽  
Siegfried Hess
Keyword(s):  
Phase Transition ◽  
Liquid Crystals ◽  
Order Parameter ◽  
Dynamic Properties ◽  
Theoretical Description ◽  
Deformation Tensor ◽  
Stationary Case ◽  
Angle Variation ◽  
Ferroelectric Liquid Crystals ◽  
First Order

AbstractA unified theoretical description of static and dynamic properties of ferroelectric liquid crystals in terms of a Landau free energy is presented. The shear deformation tensor is used as principal order parameter. Results for the stationary case for tilt angle variation and dielectric properties are compared with experiments on a compound with a pronounced first-order SmA-SmC* phase transition for various strengths of the applied electric field

scholarly journals INFLUENCE OF PRESSURE ON SMECTIC A-NEMATIC PHASE TRANSITION

1999 ◽  
Vol 13 (09n10) ◽  
pp. 275-283 ◽  
Author(s):  
KISOR MUKHOPADHYAY ◽  
PRABIR K. MUKHERJEE
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Phenomenological Model ◽  
Order Parameter ◽  
Nematic Phase ◽  
Tricritical Point ◽  
Second Order ◽  
Experimental Results ◽  
First Order ◽  
Smectic A

We propose a Landau-de Gennes phenomenological model to describe the pressure induced smectic A-nematic phase transition. The influence of pressure on smectic A-nematic phase transitions are discussed for varying coupling between orientational and translational order parameter with pressure. Increasing the pressure, the first order nematic-smectic A transition becomes second order at a tricritical point which agrees fairly well with available experimental results.

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