323,122 research outputs found
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
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
Annihilation of edge dislocations in smectic A liquid crystals
No full textThis paper presents a theoretical study of the annihilation of edge dislocations in the same smectic plane in a bulk smectic-A phase. We use a time-dependent Landau-Ginzburg approach where the smectic ordering is described by the complex order parameter psi( r--> ,t) =eta e(iphi) . This quantity allows both the degree of layering and the position of the layers to be monitored. We are able to follow both precollision and postcollision regimes, and distinguish different early and late behaviors within these regimes. The early precollision regime is driven by changes in the phi ( r--> ) configuration. The relative velocity of the defects is approximately inversely proportional to the interdefect separation distance. In the late precollision regime the symmetry changes within the cores of defects also become influential. Following the defect collision, in the early postcollision stage, bulk layer order is approached exponentially in time. At very late times, however, there seems to be a long-time power-law tail in the order parameter fluctuation relaxation
Dimerization in trans-4-butylcyclohexanecarboxylic acid and in its mixture with 12% cis-isomer observed via H- and D- NMR
No full textSurface depinning of smectic-A dislocations
No full textUsing a Landau–de Gennes approach, we model the formation of an edge dislocation in a smectic-A cell initially in the bookshelf structure. The driving force is the mismatch between the layer thickness in a bulk smectic-A liquid crystal and that imposed by confining plates. The core structure of the dislocation is calculated taking into account spatial variations of the smectic translational order parameter. We numerically determine the critical condition for the surface-driven formation and depinning of the dislocation. By exploiting this phenomenon, we show how the value of the positional anchoring strength at the surface can be determined
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
Screen cues to flatness do affect 3d percepts
No full textWatt SJ, Banks MS, Ernst MO, Zumer JM. Screen cues to flatness do affect 3d percepts. Journal of Vision. 2002;2(7):297
Surface induced nematic ordering and localization of twisted distortion in a nematic cell
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