72 research outputs found
Is internal order in 2D nematic systems destroyed by boundary disorder?
No full textComputer simulations of 2D nematic systems with quenched disorder placed on the oriented boundary have been performed to test the Feldman-Vinokur hypothesis which suggests that the long-range order is destroyed in that case. Our results for various system sizes and different percentages of disorder at the boundary do not necessarily confirm this hypothesis
Elastic anisotropy and anchoring effects on the textures of nematic films with random planar surface alignment
No full textWe present aMonte Carlo study of topological defects in nematic films with random planar boundary conditions. The polarized microscopy images and their evolution are analysed in uniaxial systems for different anchoring strengths and film thicknesses
A microscopic lattice model for liquid crystal elastomers
No full textWe propose a simple coarse-grained lattice model for liquid crystal elastomers and show, through large scale Monte Carlo simulations,
that it can reproduce stress–strain, order, light transmission, and other experiments, including temperature effects. We
focus both on homogeneously and inhomogeneously crosslinked materials
Monte Carlo Simulations of a Composite Liquid Crystal-Polymer Model System
No full textWe present a Monte Carlo study of a simple model of a liquid crystal-polymer system under the effect of an external applied field. A lattice spin model, based on the Lebwhol-Lasher Hamiltonian and generalized with suitable boundary conditions, has been employed to investigate the molecular organization and to predict the ordering across a sample cell
Lattice spin simulations of low power photonic liquid-crystal devices
No full textWe have performed a detailed Monte Carlo study of photonic devices based on nematic liquid crystal infiltrated in polydimethylsiloxane (PDMS) and in Silicon-Organic Hybrid (SOH) channels, to be used as waveguides. The simulations of a simple model of these slot waveguide shifters have shown the effect of an applied electric external field in two cases with different surface alignments, i.e. planar SOH and homeotropic PDMS. We have investigated the effect of the external field on the optical transmission and the ordering across the cell
Nematics with dispersed polymer networks: from lattice spin models to experimental observables
No full textWe report our Monte Carlo studies of molecular ordering in nematic liquid crystals with dispersed polymer networks. Starting from the aligning effect of a single fiber, we study different network topographies and investigate regular and random arrays of straight and distorted polymer fibrils. We analyze the aligning ability of rough fibrils, external field-induced switching, and pretransitional ordering. The simulation output is used to calculate selected experimental observables: 2H NMR spectra, capacitance, and intensity of transmitted polarized light
A distributed computing approach to the simulation of liquid crystal lattice models
No full textWe have studied a lattice spin model of nematic liquid crystal-polymer composite films by means of extensive Monte Carlo simulations over a distributed computing network. The Condor processing system installed on the Italian Nuclear Physics Institute computer network was used. The use of several geometries and boundary conditions allowed us to investigate a wide number of different realistic or speculative models. Many of the simulations differ only by a small number of parameters and they can be effectively performed in parallel. The results of the simulations can be analyzed globally when all the computations are completed and then for example, employed to extrapolate Phase Diagrams or other complex physical quantities, They provide an effective example of wide area distributed computing applications which could be also implemented in future GRID approaches
Computer simulations of liquid crystals and polymers
No full textLiquid crystals, polymers and polymer liquid crystals are soft condensed matter systems of major technological and scientific interest. An understanding of the macroscopic properties of these complex systems and of their many and interesting peculiarities at the molecular level can nowadays only be attained using computer simulations and statistical mechanical theories. Both in the Liquid Crystal and Polymer fields a considerable amount of simulation work has been done in the last few years with various classes of models at different special resolutions, ranging from atomistic to molecular and coarse-grained lattice models. Each of the two fields has developed its own set of tools and specialized procedures and the book aims to provide a state of the art review of the computer simulation studies of polymers and liquid crystals. This is of great importance in view of a potential cross-fertilization between these connected areas which is particularly apparent for a number of experimental systems like, e.g. polymer liquid crystals and anisotropic gels where the different fields necessarily merge. An effort has been made to assess the possibilities of a coherent description of the themes that have developed independently, and to compare and extend the theoretical and computational techniques put forward in the different areas
Lattice spin models of polymer-dispersed liquid crystals
No full textMonte Carlo simulations of lattice spin models are a powerful method for the investigation of confined nematic liquid crystals and allow for a study of the molecular organization and thermodynamics of these systems.
Investigations of models of polymer-dispersed liquid crystals are
reviewed devoting particular attention to the calculation of deuterium NMR spectra from the simulation data
Computer Simulations and experimental dynamical characterization of a composite liquid crystal-polymer system
No full textWe present a Monte Carlo study of a simple model of a liquid crystal-polymer system under the effect of an external applied field. A lattice spin model, based on the Lebwhol-Lasher Hamiltonian and generalized with suitable boundary conditions, has been employed to investigate the molecular organization and to predict the ordering across a sample cel
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