Sharif Digital Repository

We present an exact treatment of the pairwise surface interactions of biaxial ellipsoidal bodies and derive the exact explicit expressions for the attractive-repulsive Lennard-Jones(6-12) ellipsoid-substrate interactions. The applicability of the results at nanoscale as a coarse-grained description of molecule-substrate interactions has been studied through presenting parameterizations for a number of small biaxial molecules. The study concludes that the anisotropic coarse-grained potential reproduces the atomistic interactions of ellipsoid-like rigid molecules perfectly, with a negligible error of less than 3%. Copyright © EPLA, 2007  

The electrohydrodynamic (EHD) vortices produced by an electric current in freely suspended liquid crystal (LC) films of N-(4-methoxybenzylidene)-4- butylaniline (MBBA), convert to a pure rotation in the presence of external electric field (E ext) perpendicular to the current direction. Here, the direction and strength of the rotation are precisely under control by our self-made device called "liquid-film motor". In this paper, we present experimental observations of the EHD fluid flow when external electric field varies from zero to a value in which pure rotation on the liquid crystal (LC) film is observed. We also show experimentally that the presence of external electric field causes a... 

This study presents a new method to develop a thin controllable retarder/modulator with spatial axial symmetry by rotating a freely suspended of 4-Cyano-4-n-pentylbiphenyl (5CB) and N-(4-methoxybenzylidene)-4-butylaniline (MBBA) liquid crystal films using mechanical method or as a liquid film motor  

The influence of Fe3O4 nanoparticles (NPs) on dielectric properties of planar and homeotropic oriented nematic liquid crystals (NLCs) were studied during the temperature interval of 298–322 °K. It was found that the dielectric permittivity was considerably increased by adding NPs mass percentages. The structural characterization of the synthesized NPs with the scale 14–18 nm has been analyzed by the X-ray diffraction and field-emission scanning electron microscopy results. The obtained dielectric anisotropy ((Formula presented.)) and mean dielectric ((Formula presented.)) have shown an immense increment in the value of 1% and 10% wt. NPs doped NLCs, respectively. These results were assigned... 

A continuum theory is employed to numerically study the equilibrium orientation and defect structures of a circular cylindrical particle with flat ends under a homeotropic anchoring condition in a uniform nematic medium. Different aspect ratios of this colloidal geometry from thin discotic to long rodlike shapes and several colloidal length scales ranging from mesoscale to nanoscale are investigated. We show that the equilibrium state of this colloidal geometry is sensitive to the two geometrical parameters: aspect ratio and length scale of the particle. For a large enough mesoscopic particle, there is a specific asymptotic equilibrium angle associated to each aspect ratio. Upon reducing the... 

Active plasmonics combined with liquid crystal (LC) has found many applications in nanophotonics. In this Letter, we propose a fast response active plasmonic device based on the interplay of the plasmonic spectrum and Fabry–Perot (FP) modes. The plasmonic spectrum and FP modes are excited in a layer of gold nanoparticle (NP) islands and an LC microcavity, respectively. The FP mode splits the extinction spectrum of the NP to narrow bands, which are named hybrid modes (HMs). Due to multiple reflections of photons inside the cavity, the extinction coefficient is enhanced compared to a bare NP layer. An external electric field shifts the HM leading to a significant increase in the figure of... 

Liquid crystal colloids have been proposed as suitable candidates for responsive photonic crystals. Large scale growth of such colloidal systems is, however, a challenge and recently template-assisted assembly has been proposed to guide the growth of colloidal crystals, with controlled symmetries, in nematic liquid crystals. Known for their long-range anisotropic interactions, these colloidal systems are stabilized typically at the center of the cells due to strong particle-wall repulsion from the confining substrates. This behaviour is dramatically changed in the presence of topographic patterning. Here we propose the use of topographic modulation of surfaces to select and localize... 

Injection locked frequency dividers (ILFD) are used for frequency division to reduce the overall power consumption. By injecting a high frequency signal to an LC oscillator, injecting signal gets synchronous with oscillator output. All ILFDs analysis reports are based on steady state solution when locking is reached. At the same time, it is important to consider transient analysis too. In this paper a simple model is developed to study phase transient analysis when injecting signal is small in amplitude. This model can be used for large signal injection as a good approximation  

The influence of Fe3O4 nanoparticles (NPs) on dielectric properties of planar and homeotropic oriented nematic liquid crystals (NLCs) were studied during the temperature interval of 298–322 °K. It was found that the dielectric permittivity was considerably increased by adding NPs mass percentages. The structural characterization of the synthesized NPs with the scale 14–18 nm has been analyzed by the X-ray diffraction and field-emission scanning electron microscopy results. The obtained dielectric anisotropy (Δε) and mean dielectric (Formula presented.) have shown an immense increment in the value of 1% and 10% wt. NPs doped NLCs, respectively. These results were assigned to the strong... 

We investigate bonded boojum-colloids in nematic liquid crystals, configurations where two colloids with planar degenerate anchoring are double-bonded through line defects connecting their surfaces. This bonded structure promotes the formation of linear chains aligned with the nematic director. We show that the bonded configuration is the global minimum in systems that favor twist deformations. In addition, we investigate the influence of confinement on the stability of bonded boojum-colloids. Although the unbonded colloid configuration, where the colloids bundle at oblique angles, is favored by confinement, the bonded configuration is again the global minimum for liquid crystals with... 

The effective interaction between spherical colloids in nematic liquid crystals is investigated in the framework of the Landau-de Gennes theory. The colloids differ in their surface interaction with the nematic liquid crystal. The particles induce quadrupolar far-field distortions in the nematic matrix, favouring homeotropic and the other degenerate planar anchoring of the nematic director. In the strong anchoring regime the colloids with homeotropic anchoring are accompanied by an equatorial disclination line defect, known as "Saturn-ring", while the colloids with degenerate planar anchoring nucleate a pair of antipodal surface defects, called "boojums". In the linear (large-distance)... 

This paper proposes an artificial pheromone communication system inspired by social insects. The proposed model is an extension of the previously developed pheromone communication system, COS-Φ. The new model increases COS-Φ flexibility by adding two new features, namely, diffusion and advection. The proposed system consists of an LCD flat screen that is placed horizontally, overhead digital camera to track mobile robots, which move on the screen, and a computer, which simulates the pheromone behaviour and visualises its spatial distribution on the LCD. To investigate the feasibility of the proposed pheromone system, real micro-robots, Colias, were deployed which mimicked insects' role in... 

Topological defects are interesting phenomena which can be observed in ordered phases such as oriented active fluids or nematic liquid crystals. Topological defects are determined by the overall structure of the director field in an active fluid in nematic phase and by exerting force to the units of the active particles they can interact or cause motion in the environment. Studying them as particles with dynamical equations, instead of studying the director field of the nematic environment, would provide us the power to study the characteristics of their motion. The equations of motion for multi-defect systems have been previously studied and in this work we focus on the chaotic properties...