Agnieszka Chrzanowska

Ordering of hard particles between hard walls

The structure of a fluid of hard Gaussian overlap particles of elongation κ = 5, confined between two hard walls, has been calculated from density-functional theory and Monte Carlo simulations. By using the exact expression for the excluded volume kernel (Velasco E and Mederos L 1998 J. Chem. Phys. 109 2361) and solving the appropriate Euler-Lagrange equation entirely numerically, we have been able to extend our theoretical predictions into the nematic phase, which had up till now remained relatively unexplored due to the high computational cost. Simulation reveals a rich adsorption behaviour with increasing bulk density, which is described semi-quantitatively by the theory without any adjustable parameters.

Density functional theory of a Gay—Berne film between aligning walls

It is shown that the simple Onsager second-virial approximation of density functional theory can successfully describe the orientational structure of a Gay-Berne film confined between aligning plates. The theory takes as input the density profile as determined by computer simulation and semi-quantitatively reproduces the variation in the nematic order parameter throughout the film, at different temperatures and for different surface potential strengths, without any adjustable parameters. In this context the validity of an earlier analytical approach is discussed where the density, order parameter and tilt angle profiles were assumed to be step functions.

Induced Anisotropy in Rapid Flows of Nonspherical Granular Materials

Flow induced formation of internal order is one of the mechanisms which are responsible for changes in the effective constitutive properties of granular materials. Especially, if the grain shapes differ significantly from a sphere the possibility of flow alignment exists and it takes not much imagination to visualize that a sliding motion of the particles is affected by their mutual alignment. The approach we are taking here is based on a continuum mechanical description of a Cosserat medium with additional internal variables describing the local order of the grain orientations. An analytical description of the problem will be presented, the validity of the Savage-Hutter theory for anisotropic granular media will be discussed, and experimental findings are compared to the theoretical results.

Kinetic-contact-driven gigantic energy transfer in a two-dimensional Lennard-Jones fluid confined to a rotating pore

A two-dimensional Lennard-Jones system in a circular and rotating container has been studied by means of molecular dynamics technique. A nonequilibrium transition to the rotating stage has been detected in a delayed time since an instant switching of the frame rotation. This transition is attributed to the increase of the density at the wall because of the centrifugal force. At the same time the phase transition occurs, the inner system changes its configuration of the solid-state type into the liquid type. Impact of angular frequency and molecular roughness on the transport properties of the nonrotating and rotating systems is analyzed.

Computational aspects of the smectization process in liquid crystals: An example study of a perfectly aligned two-dimensional hard-boomerang system

A replica method for calculation of smectic liquid crystal properties within the Onsager theory has been presented and applied to an exemplary case of two-dimensional perfectly aligned needlelike boomerangs. The method allows one to consider the complete influence of the interaction terms in contrast to the Fourier expansion method which uses mostly first or second order terms of expansion. The program based on the replica algorithm is able to calculate a single representative layer as an equivalent set of layers, depending on the size of the considered width of the sample integration interval. It predicts successfully smectic density distributions, energies, and layer thicknesses for different types of layer arrangement-of the antiferroelectric or of the smectic A order type. Specific features of the algorithm performance and influence of the numerical accuracy on the physical properties are presented. Future applications of the replica method to freely rotating molecules are discussed.

Surface Pattern Formation in 2D System of Liquid Crystalline Molecules

Two-dimensional liquid crystal systems attract recently great attention due to their potential applications in photoelectronic industry. Typically they are formed by the molecules of mesogenic character confined to a surface. They can form then a thin film whose optical properties strongly depend on the type and degree of ordering. This ordering is determined by the state parameters such as density or temperature as well as by the shape of the constituent particles. In order to study these ordering properties a model of two-dimensional hard discorectangles has been considered. Using the Onsager type of the density functional theory the ordering of discorectangles on surfaces has been here presented with the focus on the lamellar formation.

Dissipation influence on cooling of 2-dimensional hard needle systems.

We discuss the occurrence of orientational clusters (bundles) which are formed in a freely cooling two-dimensional system of granular hard needles. This phenomenon can be present in the isotropic as well as in the nematic phase. In the nematic phase, bundles are the reason for the global decrease of the order parameter with a simultaneous decrease of the system temperature. Such a feature stands in sharp contrast to genuine liquid crystals where a decrease of temperature is always associated with an increase of the order parameter. Properties of hard needles confined in a pipe are presented for elastic and dissipative walls. It has been observed that even small dissipation at the walls leads to significant density and orientation instabilities. We also detect micro-flows that depend on the distance from the wall.