Landau theory

About: Landau theory is a research topic. Over the lifetime, 2882 publications have been published within this topic receiving 57078 citations.

Global phase diagrams of binary dipolar fluid mixtures

Abstract: We apply a modified mean-field density functional theory to determine the phase behaviour of binary mixtures of Stockmayer fluids whose spherical constituents interact according to Lennard-Jones (LJ) pair potentials with embedded pointlike dipole moments. On the basis of systematic numerical calculations we construct the global phase diagrams of these systems in the three-dimensional thermodynamic space of temperature, pressure and chemical potential difference of the two components. The vapour–liquid, isotropic liquid–isotropic liquid, isotropic liquid–ferromagnetic liquid and ferromagnetic liquid–ferromagnetic liquid first-order phase separations are investigated. The loci of the second-order isotropic fluid–ferromagnetic fluid transition are calculated from Landau theory. Liquid–vapour and liquid–liquid critical lines, tricritical lines, triple lines and lines of critical end points of the binary Stockmayer mixtures are also determined. We discuss how the topology of the phase diagrams changes upon var...

Critical behavior in anchoring transitions of nematic liquid crystals.

Abstract: The adsorption of water onto a crystal surface can result in a first-order transition in the orientation of the director of a nematic liquid crystal spread on top of the surface. Here, we show that coadsorption of two or three chemicals can lead to a phase diagram having first-order transition boundaries, critical lines, and critical points. A simple Landau theory accounts for most of the phenomena we observe. This experiment gives the first direct optical visualization of a two-dimensional system near its critical point.

Defect-induced incompatibility of elastic strains: Dislocations within the Landau theory of martensitic phase transformations

Abstract: In dislocation-free martensites the components of the elastic strain tensor are constrained by the Saint-Venant compatibility condition which guarantees continuity of the body during external loading However, in dislocated materials the plastic part of the distortion tensor introduces a displacement mismatch that is removed by elastic relaxation The elastic strains are then no longer compatible in the sense of the Saint-Venant law and the ensuing incompatibility tensor is shown to be proportional to the gradients of the Nye dislocation density tensor We demonstrate that the presence of this incompatibility gives rise to an additional long-range contribution in the inhomogeneous part of the Landau energy functional and to the corresponding stress fields Competition among the local and long-range interactions results in frustration in the evolving order parameter (elastic) texture We show how the Peach-Koehler forces and stress fields for any distribution of dislocations in arbitrarily anisotropic media can be calculated and employed in a Fokker-Planck dynamics for the dislocation density This approach represents a self-consistent scheme that yields the evolutions of both the order parameter field and the continuous dislocation density We illustrate our method by studying the effects of dislocations on microstructure, particularly twinned domain walls, in an Fe-Pd alloy more » undergoing a martensitic transformation « less