the boundary between the aggregate and its environment, The microstructure of kerosene-based magnetite colloids, stabithere exists the surface tension and so in zero field the aggrelized by oleic acid, has been studied using rheological, diffusion, gates are of spherical shape. Under the applied field they and magnetic measurements. It is shown that more than half of extend along the field and transform into thin fibers. Alall the particles are associated in quasi-spherical microaggregates though the drop-like aggregates of such a form already rewith Neel's relaxation mechanism of the magnetic moment. These semble long chains, we will distinguish between these two aggregates, containing up to several tens of particles, are formed kinds of aggregates. Being relatively large macroscopic obdue to molecular forces and are stable with respect to temperature jects, the drop-like aggregates do not take part in Brownian alteration. Another type of aggregate is represented by short stiff chains. They have been observed in colloids which contain at a motion, unlike the microscopic chain aggregates, the crossleast small number of large (Γ20 nm) particles. These aggregates, size of which is equal to the colloid particle diameter. With comprising up to 4-5 particles, are formed in a reversible way the magnetic field off, the drop-like aggregates (unlike the under temperature variation and are characterized by a Brownian chain aggregates) again take spherical shape.
relaxation mechanism of the magnetic moment. α§ 1996 Academic
The appearance of drop-like aggregates breaks up the uni-Press, Inc.
formity of the colloid solution, which is separated into phases