Phase behavior of bidisperse ferrocolloids

Abstract

The phase behavior of bidisperse ferrocolloids consisting of binary mixtures of dipolar hard spheres (DHS's) with different particle diameters and different dipole moments is investigated using density-functional theory in a modified mean-field approximation. We focus on the fluid phase regime, where we consider both isotropic and anisotropic states. Depending on the parameter Gamma -measuring the asymmetry of the dipolar couplings-the systems display complex fluid-fluid phase behavior involving demixing transitions, as well as first- and second-order isotropic-to-ferromagnetic phase transitions. The topology of the resulting phase diagrams turns out to be similar to those corresponding to monodisperse DHS mixtures investigated previously by us [Phys. Rev. E 69, 041201 (2004)]]. However, additional size asymmetry has a strong impact on the relative importance of the various types of phase transitions. In particular, the demixing transition of bidisperse ferrocolloids is strongly destabilized compared to that of monodisperse DHS's in the sense that demixing critical points are significantly shifted towards lower temperatures.

Phase transitions and ordering of confined dipolar fluids

“…The phase diagrams exhibit the usual liquid-gas critical point, a triple point, a tricritical point, and a line of critical points corresponding to second-order phase transitions between the isotropic and the ferromagnetic liquid. For bulk dipolar fluids these phase transitions and critical points and lines have been detected in various theoretical studies [12][13][14][15][16].…”

Magnetization and susceptibility of ferrofluids

“…Within this approach the LJ interaction parameters are considered to be effective ones, incorporating the effects of the solvent. (In a more refined approach one would model the suspension as a binary mixture of a nonpolar solvent and a polar solute component [5,6]. )…”

The magneto-optical behaviors modulated by unaggregated system for γ-Fe2O3–ZnFe2O4 binary ferrofluids

“…36 In the absence of a magnetic field, the chained γ -Fe 2 O 3 particles (A particles) and unchained ZnFe 2 O 4 particles (B particles) are likely to be uniformly mixed, because their sizes show an overlapping distribution. When a magnetic field is applied, a demixing phase transition may be induced, since the mean moment <m A > is larger than the mean moment <m B > ( = (<m B 2 > / <m A 2 >) < 1).…”