Planar nematic liquid crystal cells doped with nanoparticles and methods of inducing a freedericksz transition (original) (raw)

Inhomogeneous Fréedericksz transition in nematic liquid crystals

Physical review. E, Statistical, nonlinear, and soft matter physics, 2002

A theoretical and experimental analysis of a spatial instability developing in a homeotropically aligned nematic liquid crystal film is presented. The explanation for the existence of this instability is supplied through an amplitude equation. This model, which is valid in the vicinity of the Fréedericksz transition, assumes a strong difference between the nematic elastic constants. The first report of such an instability observed in the conditions accounted for by our model, was provided by Cladis and Torza [J. Appl. Phys. 6, 584 (1975)]. We repeated these experiments in order to confirm the validity of the model. Although carried out far from the Fréedericksz transition, these latter show a good qualitative agreement with the theoretical predictions. The nonlinear analysis allows to understand the dynamical behavior of an interface separating domains of stripes through the occurrence of a zigzag instability.

Periodic saddle-splay Freedericksz transition in nematic liquid crystals

The European Physical Journal E, 2005

By use of a local stability criterion recently introduced, we predict the existence of a periodic saddle-splay Freedericksz (PSSF) transition that adds to the existing class of classical Freedericksz transitions driven in a nematic cell by an external field. Occurrence of the PSSF transition requires a saddle-splay elastic constant with a large enough magnitude and different anchoring strengths at the plates confining the nematic cell. Otherwise, either the PSSF transition does not occur at all, or it requires a field higher than that associated with the classical aperiodic splay Freedericksz (ASF) transition, in which case it is not observable. Here, we determine the threshold field for which the PSSF precedes the ASF transition, as well as the structure of the destabilizing mode.

Temperature Dependence of Freedericksz Transition in Nematic Liquid Crystals with Quantum Dots

2018

Nematic liquid crystals (NLC), widely used in many devices due to the low power consumption of LCD are more often used as a host medium for different kinds of nanoparticles such as carbon nanotubes [1, 2, 3] ferromagnetic nanoparticles [4, 5], ferroelectric nanoparticles [6] or recently discovered quantum dots [7, 8, 9]. Thus, the mechanic, electric, magnetic or optic properties of the nanoparticles can be studied, and new nanotechnologies can be developed. Thermotropic nematic liquid crystals consist of rod like molecules presenting a crystalline order in liquid phase on a certain temperature range. They present dielectric anisotropy so, when an external electric field is applied the molecule’s long axis changes its orientation. Due to elastic interactions between the molecules, this reorientation appears only if a critical value of the field is reached (Freedericksz transition threshold). This threshold field depends on LC’s elastic properties but also on molecular orientation ins...

Periodic Splay-Twist Fréedericksz Transition in Nematic Liquid Crystals

Physical Review Letters, 1986

This paper derives theoretical results for the periodic splay-twist Fréedericksz transition in nematic liquid crystals confined between two infinite concentric cylinders. The calculation of Lonberg and Meyer ͓Phys. Rev. Lett. 55, 718 ͑1985͔͒, for nematics sandwiched between two infinite planes, is extended to annular domains. The phase transition is triggered by an applied voltage between the outer and the inner delimiting walls. The critical threshold behavior is analyzed via the linearized Euler-Lagrange equations related to the Frank's free energy. It is found that, the threshold depends on both the ratio between the twist and the splay elastic constants, and the sample radii ratio. Results for planar samples are recovered in the thin cell limit. With respect to the planar geometry, our analysis predicts that for annular geometries the periodic Fréedericksz transition is also allowed for elastic anisotropies K 2 / K 1 Ͼ 0.303.

Light-induced Freedericksz transition in turbid layers of nematic liquid crystal

Optics and Spectroscopy, 1985

This paper describes the implementation of a web-based application for the student registration system using Java Server Faces (JSF). JSF is a standardized specification for building User Interfaces (UI) for a client and server-side based applications. We all know the struts framework which is popular for building JSP web-based application framework and Swing framework for desktop applications. JSF is a mixture of the two frameworks. The lifecycle of a web application is managed by JSF through a controller servlet. JSF provides an enhanced mechanism to handle events and to render the components. This paper describes briefly about introduction to JSF and what it means and how we use that to create several applications using JSF UI components.

Comment on “Colloidal Interactions and Transport in Nematic Liquid Crystals”

Physical Review Letters, 2008

We describe a new nematic liquid-crystal colloid system which is characterized by both charge stabilization of the particles and an interaction force. We estimate the effective charge of the particles by electrophoretic measurements and find that in such systems the director anchoring energy W is very low and the particles have little director distortion around them. The interaction force is created by producing a radial distribution of the nematic order parameter around a locally isotropic region created by ir laser heating. We theoretically describe this as being due to the induced flexoelectric polarization, the quadrupolar symmetry of which provides the required long-range force acting on charged particles.

Microparticles confined to a nematic liquid crystal shell

Soft Matter, 2013

A seminal paper [D. R. Nelson, Nano Lett., 2002 has proposed that a nematic coating could be used to create a valency for spherical colloidal particles through the functionalization of nematic topological defects. Experimental realizations however question the complex behaviour of solid particles and defects embedded in such a nematic spherical shell. In order to address the related topological and geometrical issues, we have studied micrometer-sized silica beads trapped in nematic shells. We underline the mechanisms that strongly modify the texture of the simple (particle-free) shells when colloidal particles are embedded. Finally, we show how the coupling between capillarity and nematic elasticity offers new ways to control the valence and directionality of shells.

Expulsion of disclinations in nematic liquid crystals

European Journal of Applied Mathematics, 2003

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, we show how 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, we show that the nematic may expel the disclination if the anchoring strength is below a critical value.