Orientational order of near D(3h) solutes in nematic liquid crystals. II. Description via Gay-Berne model with embedded quadrupoles.

We perform Monte Carlo simulations of a mixture of soft ellipsoids with embedded quadrupoles as a model of various chloro- and methyl-substituted benzenes dissolved in nematic liquid crystals. We find that oblate Gay-Berne ellipsoids with multiple embedded quadrupoles qualitatively reproduce the trend in the order parameter asymmetry experimentally observed in NMR spectra. The trend is opposite to what is expected on the basis of the interaction of the solute's quadrupole with the solvent's average electric field gradient "felt" by dissolved dihydrogen molecules.

Bridging the gap between phenomenology and microscopic theory: asymptotes in nematic colloids.

The Ornstein-Zernike equation is applied to nematic colloids with up-down symmetry to determine how the electrostatic analogy and other phenomenological results appear in molecular theory. In contrast to phenomenological approaches, the molecular theory does not assume particular boundary conditions (anchoring) at colloidal surfaces. For our molecular parameters the resulting anchoring appears to be realistic, neither rigid nor infinitely weak.

Tracer diffusion in hard sphere fluids from molecular to hydrodynamic regimes.

Molecular dynamics is employed to investigate tracer diffusion in hard sphere fluids. Reduced densities (rho*=rhosigma(3), sigma is the diameter of bath fluid particles) ranging from 0.02 to 0.

Nematic-fluid structure in wall-field geometry. II. The direct correlation function.

An explicit expression for the wall-nematic direct correlation function (DCF) is obtained for any orientation of the wall with respect to an external orienting field. It is found that inside the surface of the wall, the DCF rapidly tends to a function of the nematogen orientation and depends only on parameters of the bulk fluid. We suggest that the wall-nematic DCF can be used as an ansatz for the colloid-nematic DCF in dilute nematic colloids.

Colloidal interactions in nematic fluids.

Microscopic theory is used to obtain effective interactions between colloidal particles in nematic fluids subjected to an external orienting field. It is shown that the field can dramatically change the effective intercolloidal interactions without altering the symmetry of the director configuration around a single particle. Our calculations suggest that a rich variety of colloidal structures can be promoted by varying the external field.

Colloid-induced structure in liquid crystal media.

The structural perturbations induced by colloidal particles immersed in a model nematic subjected to an external field are calculated employing integral equation methods. Maps of the density-orientational distribution about a colloidal particle are obtained, and these provide a microscopic picture of the colloid's nematic coat. We focus on colloidal particles that favor homeotropic anchoring, but planar anchoring cases are also considered.

Nematic fluid structure in wall-field geometry.

We describe an integral equation method for obtaining the distribution of a nematic fluid near a wall and interacting with a uniform orienting field. Complete density-orientational profiles are calculated for a model nematic with different wall-particle interactions and different orientations of the wall with respect to the field. For orienting walls we identify particular long-range correlations that are responsible for reorientation of the bulk nematic at zero external field.

Surface-induced ordering of nematics in an external field: the strong influence of tilted walls.

Microscopic theory is used to investigate surface-induced order in a model nematic subjected to an external orienting field. The wall-particle interaction tends to orient particles perpendicular to the surface. It is shown that if the wall is tilted at approximately 45 degrees to the field, the reorientational effects can be an order of magnitude larger than those observed for perpendicular or parallel orientations.

Model fluid in a porous medium: results for a Bethe lattice.

We consider a lattice gas with quenched impurities or "quenched-annealed binary mixture" on the Bethe lattice. The quenched part represents a porous matrix in which the (annealed) lattice gas resides. This model features the three main factors of fluids in random porous media: wetting, randomness, and confinement.

Possible new phase of antagonistic nematogens in a disorienting field.

A simple model is proposed for nematogenic molecules that favor perpendicular orientations as well as parallel ones. (Charged rods, for example, show this antagonistic tendency.) When a small disorienting field is applied along z, a low-density phase N- of nematic order parameter S(z)<0 coexists with a dense biaxial nematic N(b).

Nematic model in the presence of a finite disorienting field: integral equation approach.

A fluid of uniaxial particles in a disorienting field is considered as a simple model of biaxial nematics. The model stability with respect to the spontaneous formation of a biaxial phase is investigated by means of the integral equation method. The orientational instability condition is obtained explicitly and turns into known results for the limiting cases of zero and of infinite fields.

Orientational ordering in fluids with partially constrained molecule orientations.

Molecular orientations in anisotropic fluids can be partially constrained as a result of electric or magnetic fields or interface influences. A statistical approach for the investigation of the orientational ordering in such systems is proposed. The long-range correlations are taken into account consistently.

[Criteria of radical sector resection in mastopathy].

Statistical investigations of morphological structure in 2 groups of patients with localized forms of fibroadenomatosis (93 observations) have been carried out. Histological findings of the morphological picture have been received both within the localized fibroadenomatosis sites and beyond them. The character of the distribution of morphological forms has been shown to remain the same in all the sites of a single and in both mammary glands.