scholarly journals Early Career Stars of the Decade

Crystals ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 52
Author(s):  
Charles Rosenblatt ◽  
Helen F. Gleeson
Keyword(s):  
Liquid Crystals ◽  
Elastic Constants ◽  
Topological Defects ◽  
Early Career ◽  
Smart Sensors ◽  
Nanoparticle Inclusions

The field of liquid crystals is constantly reinventing itself, evolving from measurements of elastic constants and devices such as the simple nematic twist cell in the 1970s to topological defects, nanoparticle inclusions, and smart sensors today [...]

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 Properties of twisted topological defects in 2D nematic liquid crystals

Soft Matter ◽  
2021 ◽  
Author(s):  
Daniel Pearce ◽  
Karsten Kruse
Keyword(s):  
Liquid Crystals ◽  
Nematic Liquid Crystals ◽  
Topological Defects ◽  
Two Dimensional

Topological defects are one of the most conspicuous features of liquid crystals. In two dimensional nematics, they have been shown to behave effectively as particles with both, charge and orientation,...

scholarly journals Extremely small twist elastic constants in lyotropic nematic liquid crystals

2020 ◽  
Vol 117 (44) ◽  
pp. 27238-27244 ◽  
Author(s):  
Clarissa F. Dietrich ◽  
Peter J. Collings ◽  
Thomas Sottmann ◽  
Per Rudquist ◽  
Frank Giesselmann
Keyword(s):  
Liquid Crystals ◽  
Elastic Constant ◽  
Elastic Constants ◽  
Nematic Phase ◽  
Elastic Moduli ◽  
Building Blocks ◽  
Lyotropic Liquid Crystals ◽  
Order Of Magnitude ◽  
Typical Range ◽  
Special Case

Recent measurements of the elastic constants in lyotropic chromonic liquid crystals (LCLCs) have revealed an anomalously small twist elastic constant compared to the splay and bend constants. Interestingly, measurements of the elastic constants in the micellar lyotropic liquid crystals (LLCs) that are formed by surfactants, by far the most ubiquitous and studied class of LLCs, are extremely rare and report only the ratios of elastic constants and do not include the twist elastic constant. By means of light scattering, this study presents absolute values of the elastic constants and their corresponding viscosities for the nematic phase of a standard LLC composed of disk-shaped micelles. Very different elastic moduli are found. While the splay elastic constant is in the typical range of 1.5 pN as is true in general for thermotropic nematics, the twist elastic constant is found to be one order of magnitude smaller (0.30 pN) and almost two orders of magnitude smaller than the bend elastic constant (21 pN). These results demonstrate that a small twist elastic constant is not restricted to the special case of LCLCs, but is true for LLCs in general. The reason for this extremely small twist elastic constant very likely originates with the flexibility of the assemblies that are the building blocks of both micellar and chromonic lyotropic liquid crystals.

Elastic Constants of Nematic Phenylpyrimidines Determined by Two Different Methods

1990 ◽  
Vol 45 (1) ◽  
pp. 37-42 ◽  
Author(s):  
A. Scharkowski ◽  
H. Schmiedel ◽  
R. Stannarius ◽  
E. Weißhuhn
Keyword(s):  
Liquid Crystals ◽  
Temperature Dependence ◽  
Elastic Constants ◽  
Optical Method ◽  
Order Parameter ◽  
Diamagnetic Susceptibility ◽  
Orientational Order ◽  
Orientational Order Parameter ◽  
H Nmr ◽  
Electric And Magnetic Fields

AbstractA survey of various methods to measure the elastic constants Ki of nematic liquid crystals is given. To determine K1, K3 and the anisotropy of the diamagnetic susceptibility Δx of two members of the 5n-hexyl-2-[4n-alkyloxy-phenyl]-pyrimidines and a mixture of both, we used a combined electromagneto- optical method, consisting in independent measurements of the optical phase difference in electric and magnetic fields acting on the same cell. The temperature dependence of the K1- and K3-values for these phenylpyrimidines can be explained by common theories. The Δx data show the same temperature dependence as the values of the orientational order parameter S obtained by 1H-NMR.

Defect Nucleation and Annihilation in Sheared Polymeric Liquid Crystals

2002 ◽  
Vol 734 ◽  
Author(s):  
Dana Grecov ◽  
Alejandro D. Rey
Keyword(s):  
Liquid Crystals ◽  
Shear Rate ◽  
Long Range ◽  
Short Range ◽  
Practical Importance ◽  
Topological Defects ◽  
Annihilation Rate ◽  
Shear Rates ◽  
Parallel Array ◽  
Defect Nucleation

ABSTRACTShear–induced nucleation and annihilation of topological defects due to hydrodynamic instability in nematic liquid crystals is a phenomenon of both scientific interest and practical importance. We use a complete generalized non-linear second order tensor Landau-de Gennes model that takes into account short range order elasticity, long-range elasticity and viscous effects, to simulate the nucleation and annihilation of twist inversion walls in flow-aligning nematic polymers subjected to shear flow. Shearing a homogeneous nematic sample perpendicular to the director results in an linear instability that maybe symmetric at low shear rates, and antisymmetric at higher shear rates. At even higher shear rates the onset of nonlinearities results in the nucleation of a parallel array of twist inversion walls, such that asymmetry prevails. By increasing the shear rate the following director symmetry transition cascade is observed: symmetric → antisymmetric → asymmetric → symmetric. The nucleation of the parallel array of twist inversion walls in the asymmetric mode is due to the degeneracy in reorientation towards the shear plane. The annihilation of twist walls is mediated by twist waves along the velocity gradient direction. Twist walls annihilate by three mechanisms: wall-wall annihilations, wall-wall coalescence, and wall-bounding surface coalescence. The annihilation rate increases with increasing shear rate and at sufficiently high rates the layered structure is replaced by a homogeneously aligned system. The role of short range and long range elasticity on defect nucleation and annihilation is characterized in terms of the Deborah and Ericksen numbers. Close form solutions to approximated equations are used to explain the numerical results of the full Landau-de Gennes equations of nematodynamics.

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