Bulk and Surface Properties of Dipolar Fluids

Abstract

Based on density-functional theory we analyze the full phase diagram, the occurrence of long-ranged orientational order, and the structural properties of dipolar fluids. As a model system we consider the Stockmayer fluid that consists of spherical particles interacting via a Lennard-Jones potential plus dipolar forces. For sufficiently strong dipole moments one finds a region where a fluid phase with long-ranged orientational order is stable. For all sample shapes with the exception of a long thin needle this phase exhibits a spatially inhomogeneous magnetization which depends on the actual shape. We determine the details of the magnetization structure in a cubic sample in the absence and in the presence of an external magnetic field. One obtains a vortexlike structure with an escape of the magnetization into the axis direction near the vortex axis and two point defects where the absolute value of the magnetization is strongly reduced. If the spherical cores of the particles are replaced by elongated or oblate shapes a nematic phase without spontaneous magnetization is also possible due to the anisotropic steric interactions. We study the interplay of this nematic ordering with ferromagnetism in fluids of dipolar hard ellipsoids. Orientational order arises locally in the isotropic fluid phases near the liquid-gas interface of the Stockmayer fluid. Density-functional theory allows us to determine density and orientational order profiles as well as the surface tension of this interface.

The structure of strongly dipolar hard sphere fluids with extended dipoles by Monte Carlo simulations

“…Both simulation and theoretical [8,9] methods prove that high density pDHS and pDSS fluids undergo a phase transition when the temperature is decreased. In the early 1990s, computer simulations of Wei and Patey [10][11][12] for the pDSS fluid and Weis and Levesque [13][14][15] for the pDHS fluid revealed the following phenomena.…”

Global phase diagrams of binary dipolar fluid mixtures

“…This is an indispensable prerequisite for studying the interfacial properties in a second step. Moreover, in view of the numerous interesting features even of bulk properties of dipolar fluids [1, 2,3], the analysis of dipolar mixtures is also important in its own right.…”

“…[1] and [2] and references therein). It considers spherical particles interacting with Lennard-Jones (LJ) potentials plus pointlike permanent dipoles at the center.…”

“…(For freezing in one-component dipolar fluids see Ref. [2] and references therein. For quasicrystalline order and glasslike structure formation in two-dimensional binary dipolar systems see Refs.…”

Accelerated inertial regime in the spinodal decomposition of magnetic fluids

“…Many groups have studied the variation of and η with respect to μ , ρ and T . 49–52 Fig. 6(a) shows the variation of with respect to μ for specified values of the reduced temperature τ = (1 − T / T c ) from ref.…”