Transport properties of an ionic magnetic colloid: experimental study of increasing the ionic strength

The phase separation of an ionic magnetic colloid in zero magnetic field by increasing the ionic strength is well known [Universite Paris VI, France, 1987; J. Colloid Interface Sci. 132 (1989) 1]. The present work deals with investigation of an ionic ferrofluid by increasing the ionic strength in the range of 0-0.14 mol/l, being safely below the threshold value at which the effect of phase separation occurs. By the optical grid setup [Fourth International conference PAMIR, France, 2000], the main transport properties of a ferrofluid, i.e. translational mass diffusion and thermal diffusion (Soret) coefficients, are measured. The obtained results show a strong dependence of mass diffusion coefficient and no dependence of the Soret coefficient upon increasing the ionic strength. It is possible to explain both these effects theoretically; nevertheless, there is the lack of an exact theoretical model due to its complexity