Interfacial tension of magnetic fluids in the mean spherical approximation

The interfacial tension coefficient for a plane and spherical interface between weakly and highly concentrate phases of magnetic fluid was evaluated in square-gradient expansion for the mean spherical approximation of dipole–dipole interaction. The method based on the minimization of free energy functional was used for solution. The density profile in the interface layer, the influence factor, Tolman length and the interfacial tension coefficient were calculated as functions of temperature and concentration using the tail of pair correlation function. The anisotropy of interfacial tension for a plane interface was calculated far from critical point in weak magnetic field. The estimations for arbitrary angles between magnetic field and interface normal were made for interfacial tension. It was shown that dependence of the interfacial tension on radius of macrodrop is negligible. Giving the expression for interfacial tension coefficient is possible and can be presented as functions of physical measured parameters: magnetic susceptibility, density and compressibility. That opens up the possibility of using these expressions for description of polydisperse magnetic fluids. The theoretical results agree well with experimental estimations.