C. Chiccoli

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.

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.

Computer Simulations of Cylindrically Confined Nematics

Abstract A Monte Carlo simulation of a nematic Lebwohl-Lasher liquid crystal confined to a cylindrical pore is presented. We have calculated the ordering and the molecular organisation inside the cavity for cylinders of different size when homeotropic radial boundary conditions and different anchoring strengths are employed. We have not observed escaped radial configurations in the organisations obtained.

Monte Carlo study of the molecular organization in model nematic droplets. Field effects

Abstract The Monte Carlo technique is used to investigate the orientational order and the molecular organization of model nematic droplets with radial boundary conditions subject to an external field. The effect of varying field strength on these model systems of polymer dispersed liquid crystals (PDLC) is also investigated.

Biaxial Nematic Droplets and their Optical Textures: A Lattice Model Computer Simulation Study

ABSTRACT Monte Carlo simulations of polarizing microscope textures for confined nematic droplets are presented. We consider uniaxial and biaxial cases with various boundary conditions and different values of the molecular biaxiality. The analysis of these optical textures should be of interest in assigning and characterizing biaxial nematic system, an issue of great current interest.