scholarly journals Molecular biaxiality determines the helical structure – infrared measurements of the molecular order in the nematic twist-bend phase of difluoro terphenyl dimer

2021 ◽  
Vol 23 (7) ◽  
pp. 4151-4160
Author(s):  
Katarzyna Merkel ◽  
Barbara Loska ◽  
Chris Welch ◽  
Georg H. Mehl ◽  
Antoni Kocot
Keyword(s):  
Order Parameter ◽  
Nematic Phase ◽  
Helical Structure ◽  
Molecular Order ◽  
Infrared Measurements

The biaxial order parameter is found to be negligible in the nematic phase, then starts increasing on entering the nematic twist-bend phase. The local director deformation was found to be determined by the molecular biaxiality parameter D.

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.

Dielectric Studies of 4-w-Hexyloxy-4’-Cyanobiphenyl (60CB) at Elevated Pressure

1999 ◽  
Vol 54 (6-7) ◽  
pp. 365-369 ◽  
Author(s):  
S. Urban ◽  
M. Smoluchowski
Keyword(s):  
Dielectric Permittivity ◽  
Order Parameter ◽  
Nematic Phase ◽  
Activation Volume ◽  
Activation Enthalpy ◽  
Ambient Pressure ◽  
Relaxation Times ◽  
Elevated Pressure ◽  
Dielectric Anisotropy ◽  
Dielectric Studies

Abstract The principal dielectric permittivity components in the nematic phase of 4-rc-hexyloxy-4’-cyanobiph-enyl (60CB) were measured as functions of temperature at ambient pressure and as functions of pres-sure up to 100 MPa at several constant temperatures. The dielectric anisotropy is analized in the frame of the Maier-Meier equations. The pressure dependence of the order parameter is deduced. Preliminary results for the activation volume and activation enthalpy from the pressure and temperature dependenc-es of the longitudinal relaxation times are obtained.

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 Phospholipase C activation by ethanol in rat hepatocytes is unaffected by chronic ethanol feeding

1990 ◽  
Vol 272 (1) ◽  
pp. 59-64 ◽  
Author(s):  
J B Hoek ◽  
T F Taraschi ◽  
K Higashi ◽  
E Rubin ◽  
A P Thomas
Keyword(s):  
Phospholipase C ◽  
Order Parameter ◽  
Plasma Membranes ◽  
Structural Changes ◽  
Rat Hepatocytes ◽  
Maximal Response ◽  
Molecular Order ◽  
Transient Activation ◽  
Ethanol Feeding

The activation of phosphoinositide-specific phospholipase C by ethanol was compared in hepatocytes isolated from ethanol-fed rats and from pair-fed control animals. Ethanol (100-300 mM) caused a dose-dependent transient increase in cytosolic free Ca2+ levels in indo-1-loaded hepatocytes from both groups of animals. The rate of Ca2+ increase was similar in hepatocytes from control and ethanol-fed rats, but the decay of the Ca2+ increase was somewhat slower in the latter preparation. The ethanol-induced Ca2+ increase caused activation of glycogen phosphorylase, with 50% response at 50 mM-ethanol and a maximal response at 150-200 mM-ethanol, not significantly different in hepatocytes from control and ethanol-fed animals. Ins(1,4,5)P3 formation in response to ethanol (300 mM) or vasopressin (2 nM or 40 nM) was also similar in the two preparations. It is concluded that long-term ethanol feeding does not lead to an adaptive response with respect to the ethanol-induced phospholipase C activation in rat hepatocytes. The ability of ethanol in vitro to decrease membrane molecular order in liver plasma membranes from ethanol-fed and control rats was measured by e.s.r. Membranes from ethanol-fed animals had a significantly lower baseline order parameter compared with control preparations (0.313 and 0.327 respectively), indicative of decreased membrane molecular order. Addition of 100 mM-ethanol significantly decreased the order parameter in control preparations by 2.1%, but had no effect on the order parameter of plasma membranes from ethanol-fed rats, indicating that the plasma membranes had developed tolerance to ethanol, similar to other membranes in the liver. Thus the membrane structural changes associated with this membrane tolerance do not modify the ethanol-induced activation of phospholipase C. The transient activation of phospholipase C by ethanol in hepatocytes may play a role in maintaining an adaptive phenotype in rat liver.

Deuterium NMR study of molecular order and conformation in the nematic phase of p‐azoxyanisole

1981 ◽  
Vol 74 (1) ◽  
pp. 633-636 ◽  
Author(s):  
Ronald Y. Dong ◽  
J. Lewis ◽  
E. Tomchuk ◽  
Chas. G. Wade ◽  
E. Bock
Keyword(s):  
Nematic Phase ◽  
Deuterium Nmr ◽  
Molecular Order ◽  
Nmr Study

scholarly journals A Bidimensional Gay-Berne Calamitic Fluid: Structure and Phase Behavior in Bulk and Strongly Confined Systems

2021 ◽  
Vol 8 ◽  
Author(s):  
A. Calderón-Alcaraz ◽  
J. Munguía-Valadez ◽  
S. I. Hernández ◽  
A. Ramírez-Hernández ◽  
E. J. Sambriski ◽  
...  
Keyword(s):  
Order Parameter ◽  
Nematic Phase ◽  
Orientational Order ◽  
Topological Defects ◽  
Md Simulations ◽  
Structural Behavior ◽  
Nematic Order ◽  
Lower Temperature ◽  
Geometry Characteristic ◽  
Strong Confinement

A bidimensional (2D) thermotropic liquid crystal (LC) is investigated with Molecular Dynamics (MD) simulations. The Gay-Berne mesogen with parameterization GB(3, 5, 2, 1) is used to model a calamitic system. Spatial orientation of the LC samples is probed with the nematic order parameter: a sharp isotropic-smectic (I-Sm) transition is observed at lower pressures. At higher pressures, the I-Sm transition involves an intermediate nematic phase. Topology of the orthobaric phase diagram for the 2D case differs from the 3D case in two important respects: 1) the nematic region appears at lower temperatures and slightly lower densities, and 2) the critical point occurs at lower temperature and slightly higher density. The 2D calamitic model is used to probe the structural behavior of LC samples under strong confinement when either planar or homeotropic anchoring prevails. Samples subjected to circular, square, and triangular boundaries are gradually cooled to study how orientational order emerges. Depending on anchoring mode and confining geometry, characteristic topological defects emerge. Textures in these systems are similar to those observed in experiments and simulations of lyotropic LCs.

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