P. Pasini

Advances in the Computer Simulations of Liquid Crystals

Preface. 1. Introduction to simulations and statistical mechanics M.P. Allen. 2. Liquid crystal observables: static and dynamic properties C. Zannoni. 3. Phase behavior of lyotropic liquid crystals D. Frenkel. 4. Modelling liquid crystal structure, phase behaviour and large-scale phenomena M.P. Allen. 5. Liquid crystal lattice models I. Bulk systems P. Pasini, et al. 6. Liquid crystal lattice models II. Confined systems P. Pasini, et al. 7. Computer simulation of lyotropic liquid crystals as models of biological membranes O.G. Mouritsen. 8. Flow properties and structure of anisotropic fluids studied by non-equilibrium molecular dynamics, and flow properties of other complex fluids: polymeric liquids, ferro-fluids and magneto-rheological fluids S. Hess. 9. Self atom-atom empirical potentials for the static and dynamic simulation of condensed phases A. Gavezzotti, G. Filippini. 10. Atomistic modelling of liquid crystal phases M.R. Wilson, et al. 11. Atomistic simulation and modeling of smectic liquid crystals M.A. Glaser. 12. Multiple time steps algorithms for the atomistic simulations of complex molecular systems P. Procacci, M. Marchi. 13. Parallel molecular dynamics techniques for the simulation of anisotropic systems M.R. Wilson. Index.

Defects in liquid crystals : computer simulations, theory, and experiments

Preface. 1. Classification of defects in liquid crystals H.-R. Trebin. 2. Alignment tensor versus director description in nematic liquid crystals A.M. Sonnet, S. Hess. 3. Liquid crystal colloidal dispersions H. Stark, et al. 4. Computer simulations and defects in confined liquid crystal lattice models C. Chiccoli, et al. 5. Molecular simulations and theory of planar interfaces and defects in nematic liquid crystals M.P. Allen. 6. Topological defect behavior in a quenched nematic liquid crystal R.A. Pelcovits, et al. 7. Restoring forces on nematic disclinations R. Rosso, E.G. Virga. 8. Challenges in the dynamics of point defects A.M. Sonnet, E.G. Virga. 9. Numerical simulation of elastic anisotropy in nematic liquid crystalline polymers H. Tu, et al. 10. Computer Simulations and Fluorescence Confocal Polarizing Microscopy of Structures in Cholesteric Liquid Crystals S.V. Shiyanovskii, et al. 11. Defects and Undulation in Layered Liquid Crystals T. Ishikawa, O.D. Lavrentovich. 12. Liquid crystals under shear: role of defects M. Kleman, C. Meyer. 13. Numerical simulation of defects in quasicrystals H.-R. Trebin. Index.

The P4 model and its orientational phase transition

A simple generalization of the Lebwohl-Lasher model, where fourth rank, rather than second rank, interactions are involved is investigated. This model was first put forward and studied some years ago using molecular field theory (Zannoni, C., 1979, Molec. Crystals liq. Crystals Lett., 49, 247). There it was found that there should be a temperature interval where the fourth rank order parameter is higher than the second rank one. This unusual behaviour has been found by various groups to be consistent with fluorescence depolarization data for diphenylhexatriene in DPPC and DMPC membrane vesicles. In this paper we investigate more thoroughly the P 4 model using Monte Carlo simulations with periodic boundary conditions on a 10 × 10 × 10 lattice and with the recently proposed Cluster Monte Carlo method on a 6 × 6 × 6 and a 10 × 10 × 10 lattice. Our results are consistent with a first order transition. We find that the results for the transition temperature and for the second and fourth rank order parameters a...

Head-tail asymmetry and ferroelectricity in uniaxial liquid crystals : model calculations

We have studied in detail a simple model system with first- and second-rank interactions first examined many years ago by Krieger and James with mean field theory and used more recently as a prototype for bowlic and ferroelectric liquid crystals. We have investigated the model applying Monte Carlo simulations and two-site cluster theory and obtained its phase diagram. The existence of a ferroelectric liquid crystal phase region in this non-chiral system is confirmed also going beyond mean field theory. We also report short and long-range order parameters of first- and second-rank as a function of temperature for various ratios of the discriminating to non-discriminating interaction.

Computer simulations of liquid crystals and polymers

1. Lattice spin Models of polymer-dispersed liquid crystals C.Chiccoli et al.Introduction, 1.Polymer-dispersed liquid crystals, 2.The simulation method, 2.1The PDLC simulation model, 2.2 Molecular ordering, 3.2H NMR, 3.1 Orientational fluctuations, 3.2 Translational diffusion.4External field effects, 4.1 Radial droplet, 4.2 Bipolar droplet. 5 Many-droplet sample.6.Conclusions 2.Nematics with dispersed polymer networks: from lattice spin models to experimental observables C.Chiccoli et al. Introduction.1.Aligning ability of the network.1.1 Planar anchoring.1.2 Homeotropic anchoring: topological defects.1.3 2 H NMR spectra. 2 External field-induced switching.2.1 Regular fiber array. 2.2 Irregular fiber array. 2.3 Experimental observables and network irregularity. 3.Pretransitional ordering in the isotropic phase.4 Conclusions. 3. Computer simulations of liquid crystal polymers and dendrimers M.R..Wilson et al. Introduction. 1.Simulation Models. 1.1 Atomistic Models, 1.2 Simplified models for polymers and liquid crystals, 2.Hybrid Models, 3.Side chain liquid crystalline polymers, 4.Main chain liquid crystalline polymer, 5.Carbosilane liquid crystalline dendrimers, 5.1 Hybrid Gay-Berne/Lennard-Jones model, 5.2 Coarse-grained model, 6.Summary. 4.Monte Carlo simulations of liquids of mesogenic oligomers Michelle and Manuela Vacatello. Introduction. 1.Trimers with polymethylene spacers, 1.1 Models and methods, 1.2 Thermal behaviour, 1.3 Orientational order in the nematic liquids,1.4 Conformational changes at the nematic/isotropic transition, 2. Dimers of series I, 3. Conclusions. 5. Molecular arrangements in polymer-nanofiller systems Michelle and Manuela Vacatello.Introduction. 1.Simulations of dense systems,1.1 Models and methods,1.2 The filler/polymer interface, 1.3 Chain conformation, 1.4Molecular arrangements, 1.5 Predicting the molecular arrangements,2.Simulations of phantom chains, 3. Conclusions. 6. Dissipative particle dynamics approach to nematic polymers A.Polimeno et al. Introduction. 1.Dissipative Particle Dynamics, 2. Methodology, 3.Standard semi-rigid segments, 4.An alternative approach, 5.Summary. 7. Some things we can learn from chemically realistic polymer melt simulations W. Paul et al. Introduction, 1.Quantitative Comparison to Experiment, 1.1 NMR Experiments, 1.2 Neutron Scattering Experiments,1.3 Dielectric Relaxation Experiments, 2. Changing the model Hamiltonian, 3. Summary 8. Monte Carlo simulations of semi-flexible polymers W. Paul et al .Introduction. 1.State Diagram of a Semi-flexible Chain, 1.1 Mean Field Scaling Theory 1.2 State Diagram, 2.Solutions of Semi-flexible Chains, 3.Summary 9.Macromolecular mobility and internal viscosity. The role of stereoregularity G. Allegra and S. Bruckner. Introduction 1.Internal viscosity, 2.Recent experimental investigations, 3.Steric hindrance to rotational propagation, 3.1 Isotactic Polystyrene (i-PS), 3.2 Syndiotactic Polystyrene (s-PS), 4.Some concluding remarks on internal viscosity and steric rotational hindrance, 10. Protein adsorption on a hydrophobic graphite surface G. Raffaini and F. Ganazzoli. Introduction. 1.Short background of theoretical and simulation methods, 2. Simulations details, 3. Initial adsorption stage in the dielectric medium, 4.Final adsorption stage by molecular dynamics in the dielectric medium, 5.Kinetics of surface spreading, 6.Hydration of the adsorbed protein fragments, 7. Conclusions and outlook to future work. 11. Multiscale simulation of liquid crystals O.Guzman et al. Introduction, 1.A multiscale model for LC-based sensors,1.1 Molecular simulations, 1.2 Dynamic Field Theory, 2.Clusters of particles, 2.1 Mapping of simulation and field theory length scales, 2.2 Sphere/substrate interactions, 2.3Two particle systems,3.Ordering kinetics in a LC-based biosensor, 4.Conclusion 12. Polymer chains and networks in narrow slits G. Allegra et al. Introduction 1. Compressed polymer networks,1.1A Gaussian chain in a harmonic potential, 1.2 The two-dimensional network, 1.3 Numerical results, 2. Polymer-mediated adhesion, 2.1 The model, 2.2 The transfer matrix, 2.3 Statistical population of loops and bridges, 2.4 Free energy, elastic forces and moduli, 3 Conclusions. 13. Rotation and deformation of polymer molecules in solutions subjected to a shear flow S. Hess and G.P. Morriss. Introduction, 1.Angular Velocity and Deformation, 2.A Simple Model, 3.Rotation and Deformation, 4.Shear-Induced Chaotic Behavior and Periodic Orbits, 5.Other Thermostats, 6.Concluding Remarks. 14. Regular and chaotic rheological behavior of tumbling polymeric liquid crystals S. Hess and G. P. Morriss Introduction, 1.The model equations, 1.1 Relaxation equation for the alignment tensor, 1.2 Constitutive relation for the pressure tensor, 1.3 Scaled variables: alignment tensor and relevant parameters, 1.4Scaled variables: stress tensor, 1.5 Basis tensors and component notation, 1.6 Characteristic solutions for the orientational dynamics, 2.Rheological behaviour, 2.1 Solutions for imposed shear rate and shear stress, 2.2 Isotropic phase and flow aligned nematic, 2.3 Tumbling nematic, 2.4 Nonzero 3. Orbits, 3.1 General remarks, flow aligned state 3.2 Kayaking-tumbling, 3.3 Tumbling, 3.4 Kayaking-wagging 3.5 Chaotic behaviour 4.Conclusions, 15. Parallel computer simulation techniques for the study of macromolecules M.R. Wilson and J.M. Ilnytskyi. Introduction. 1. Parallelisation: the basic concepts, 2. Parallel molecular dynamics: the replicated data approach, 3.Parallel molecular dynamics: the domain decomposition approach, 4. Parallel Monte Carlo, 5.Summary, Index

A computer simulation of nematic droplets with radial boundary conditions

Abstract We present Monte Carlo simulations of nematic droplets with radial boundary conditions and we investigate the orientational order and the molecular organizations in these systems that mimic polymer dispersed liquid crystals (PDLC).

A DETAILED MONTE CARLO INVESTIGATION OF THE TRICRITICAL REGION OF A BIAXIAL LIQUID CRYSTAL SYSTEM

We study a lattice system of biaxial particles interacting with a second-rank anisotropic potential. We have performed detailed Monte Carlo calculations in the vicinity of the prolate–oblate dual value of molecular biaxiality. Our results confirm the second-order character of the transition in this limiting case.

A Monte Carlo investigation of the planar Lebwohl-Lasher lattice model

A Monte Carlo computer simulation of a planar version of the Lebwohl-Lasher model is presented. The model consists of a set of interaction centres forming a simple square lattice. The pair potential is nearest-neighbours, attractive, and varies as a second Legendre polynomial of the relative orientation between the two particles. Five lattice sizes, 5 × 5, 10 × 10, 20 × 20, 60 × 60 and 80 × 80, of this two-dimensional system have been simulated with Monte Carlo and periodic boundary conditions. A study of the orientational pair correlation function indicates a power law decay in the ordered phase and an exponential decay above the pseudo-transition temperature. Our results are consistent with the absence of a true phase transition but also indicate a low-temperature phase with long short-range order. Comparisons are made with one existing simulation and with the mean field theory results.

Computer Simulations of Nematic Droplets with Toroidal Boundary Conditions

Abstract We present Monte Carlo simulations of nematic droplets with toroidal boundary conditions (TBC) and various anchoring strengths and we investigate the orientational order and the molecular organizations in these systems that mimic polymer dispersed liquid crystals (PDLC). PACS: 02.50 Monte Carlo studies PACS: 61.30.Jf Defects in liquid crystals PACS: 61.30.Gd Orientational order of liquid crystals PACS: 64.70.M Liquid Crystals phase transitions.

Monte Carlo simulations of model nematic droplets

Abstract We present Monte Carlo computer simulations of model nematic droplets with radial boundary conditions and various anchoring strengths and we investigate the orientational order and the molecular organizations in these systems that mimic polymer dispersed liquid crystals (PDLC). We find a hedgehog organization at high anchoring strengths and that an ordered domain is created in the droplet center at lower strengths.