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CPP: Chemische Physik und Polymerphysik

CPP 30: POSTER: Chemical physics

CPP 30.29: Poster

Dienstag, 8. März 2005, 16:30–18:30, Poster TU D

Density functional study of the phase behavior of bidisperse ferrocolloids in external fields — •Gabriel M. Range and Sabine H. L. Klapp — Stranski-Laboratorium für Physikalische und Theoretische Chemie, Sekretariat TC 7, Fakultät II für Mathematik und Naturwissenschaften, Technische Universität Berlin, Straße des 17. Juni 124, D-10623 Berlin, Germany

The phase behavior of bidisperse ferrocolloids, consisting of binary mixtures of dipolar hard spheres (DHS), is investigated using density functional theory in the modified mean-field approximation. We focus on the fluid phase regime, where we consider both isotropic and anisotropic phases.
In the absence of external magnetic fields our results reveal complex fluid-fluid phase behavior involving demixing and first- and second-order isotropic-to-ferroelectric phase transitions. Dependent on the asymmetry of the mixture, measured by a parameter Γ, we encounter three different types of phase behavior, differing in the degree to which demixing dominates the system.
In strong magnetic fields we observe only two such types distinguished by the behavior of the line of triple points. External fields have negligible effect on the demixing transitions of weakly asymmetric mixtures, while gas-liquid transitions are influenced similarly to the one-component case. Strongly asymmetric mixtures, however, show a strong destabilization of the high-temperature coexistences which are the result of an interplay of demixing and ordering transitions.