Chain-like aggregates in magnetic fluids

Experimental investigation was carried out to detect in magnetic fluids the hypothetical aggregates analogous to polymer chains. The emphasis was placed on the method of studying low-frequency behavior of the magnetic fluids in crossed magnetic fields because this method is highly sensitive to the presence of chains in colloidal solutions. The theory of the method was improved in such a way that in the analysis of the results one can take into account the natural polydispersity of particles, interparticle interaction and demagnetization factor of the sample. The colloidal solutions of magnetite in decane with oleic acid used as a surfactant were investigated in a wide range of magnetic bias fields and magnetic phase concentration. In highly concentrated solutions no chains were detected whereas in diluted solutions the existence of short chains is the fact beyond question. The chains consist of three particles at the average and accumulate up to several percents of colloidal particles. The results of experiments were compared with predictions of the theoretical models.