Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userQuantum-Dots Dispersed Bent-core Nematic Liquid Crystals and Cybotactic Clusters: Experimental and Theoretical Insights
108
0
0.0
(
0
)
Added by
Sourav Patranabish Mr.
Publication date
2020
fields
Physics
and research's language is
English
Ask ChatGPT about the research
No Arabic abstract
We study a quantum-dots (QDs) dispersed bent core liquid crystalline system in planar geometry and present experimental measurements of the order parameter, dielectric dispersion and absorption spectra, optical textures, with attention to variations with temperature. A bent core liquid crystal (LC) 14-2M-CH$_3$ is used as the host material and CdSe/ZnS core-shell type QDs are used as the dopant. The nematic (N) phase exhibited by the pristine (undoped) LC 14-2M-CH$_3$ contains cybotactic clusters, which are retained by its QDs incorporated LC nanocomposite. Our notable findings concern the reduction of the orientational order parameter of the QDs dispersed LC system compared to its pristine counterpart, at fixed temperatures, and a reduction of the size of the cybotactic clusters due to the incorporation of QDs. The reduced order parameter for the doped system is accompanied by reduced birefringence, increased activation energy and a qualitative reduction in the dielectric anisotropy. We complement the experiments with a novel Landau-de Gennes type free energy for a doped bent core LC system, that qualitatively captures the doping-induced reduced order parameter and its variation with temperature. The dependency of the mean order parameter on several other factors (e.g. cluster size, coupling parameter) are also analyzed.
rate research
Read More
The bent-core liquid crystals (LCs) are highly regarded as the next-generation materials for electro-optic devices. The nematic (N) phase of these LCs possesses highly ordered smectic-like cybotactic clusters which are promising in terms of ferroelectric-like behaviour in the N phase itself. We have studied a one-dimensional (1D) Landau-deGennes model of spatially inhomogeneous order parameters for the N phase of bent-core LCs. We investigate the effects of spatial confinement and coupling (between these clusters and the surrounding LC molecules) on the order parameters to model cluster formation in recently reported experiments. The coupling is found to increase the cluster order parameter significantly, suggesting an enhancement in the cluster formation and could also predict a possible transition to a phase with weak nematic-like ordering in the vicinity of nematic-isotropic transition upon appreciable increase of the coupling parameter {gamma}.
We present in this paper a detailed analysis of the flexoelectric instability of a planar nematic layer in the presence of an alternating electric field (frequency $omega$), which leads to stripe patterns (flexodomains) in the plane of the layer. This equilibrium transition is governed by the free energy of the nematic which describes the elasticity with respects to the orientational degrees of freedom supplemented by an electric part. Surprisingly the limit $omega to 0$ is highly singular. In distinct contrast to the dc-case, where the patterns are stationary and time-independent, they appear at finite, small $omega$ periodically in time as sudden bursts. Flexodomains are in competition with the intensively studied electro-hydrodynamic instability in nematics, which presents a non-equilibrium dissipative transition. It will be demonstrated that $omega$ is a very convenient control parameter to tune between flexodomains and convection patterns, which are clearly distinguished by the orientation of their stripes.
We analyze the interaction with uniform external fields of nematic liquid crystals within a recent generalized free-energy posited by Virga and falling in the class of quartic functionals in the spatial gradients of the nematic director. We review some known interesting solutions, i. e., uniform heliconical structures, which correspond to the so-called twist-bend nematic phase and we also study the transition between this phase and the standard uniform nematic one. Moreover, we find liquid crystal configurations, which closely resemble some novel, experimentally detected, structures called Skyrmion Tubes. Skyrmion Tubes are characterized by a localized cylindrically-symmetric pattern surrounded by either twist-bend or uniform nematic phase. We study the equilibrium differential equations and find numerical solutions and analytical approximations.
In 3D nematic liquid crystals, disclination lines have a range of geometric structures. Locally, they may resemble $+1/2$ or $-1/2$ defects in 2D nematic phases, or they may have 3D twist. Here, we analyze the structure in terms of the director deformation modes around the disclination, as well as the nematic order tensor inside the disclination core. Based on this analysis, we construct a vector to represent the orientation of the disclination, as well as tensors to represent higher-order structure. We apply this method to simulations of a 3D disclination arch, and determine how the structure changes along the contour length. We then use this geometric analysis to investigate three types of forces acting on a disclination: Peach-Koehler forces due to external stress, interaction forces between disclination lines, and active forces. These results apply to the motion of disclination lines in both conventional and active liquid crystals.
Investigations of the phase diagram of biaxial liquid crystal systems through analyses of general Hamiltonian models within the simplifications of mean-field theory (MFT), as well as by computer simulations based on microscopic models, are directed towards an appreciation of the role of the underlying molecular-level interactions to facilitate its spontaneous condensation into a nematic phase with biaxial symmetry. Continuing experimental challenges in realising such a system unambiguously, despite encouraging predictions from MFT for example, are requiring more versatile simulational methodologies capable of providing insights into possible hindering barriers within the system, typically gleaned through its free energy dependences on relevant observables as the system is driven through the transitions. The recent brief report from this group [B. Kamala Latha, et. al., Phys. Rev. E 89, 050501 (R), 2014] summarizing the outcome of detailed Monte Carlo simulations carried out employing entropic sampling technique, suggested a qualitative modification of the MFT phase diagram as the Hamiltonian is asymptotically driven towards the so-called partly-repulsive regions. It was argued that the degree of the (cross) coupling between the uniaxial and biaxial tensor components of neighbouring molecules plays a crucial role in facilitating, or otherwise, a ready condensation of the biaxial phase, suggesting that this could be a plausible f actor in explaining the experimental difficulties. In this paper, we elaborate this point further, providing additional evidences from curious variations of free-energy profiles with respect to the relevant orientational order parameters, at different temperatures bracketing the phase transitions.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
