Magnetizable colloids on strongly polar carriers – preparation and manifold characterization

Abstract

The aim of this paper is to present methods applied to obtain and to investigate the properties of magnetic fluids on strongly polar carrier liquids, such as short-chain-length alcohols and water. The high degree of colloidal stability of these colloids is achieved by double-layer sterical stabilization of Fe₂O₃ and CoFe₂O₄nanoparticles dispersed in the carrier liquid, the adequate choice and efficient adsorption of the surfactant(s) used being one of the key problems to be solved in each particular case, in order to obtain high-quality magnetic fluids. The samples were investigated using a vibrating-sample magnetometer, a rheo/magnetorheometer with various measuring cells, as well as by small-angle neutron scattering, in order to detect magnetic-field-induced changes at the nanometric level and qualitative differences in the macroscopic behaviour of various samples. The conclusions refer to the dependence of the colloidal stability on the composition and volumic concentration of the magnetic fluid samples, as well as on the applied magnetic field.

Acknowledgements. The permanent support of Prof. Ioan Anton, a member of the Romanian Academy, was of great help to develop and to perform the many investigations on the structure and flow properties of magnetic fluids presented in this paper. The financial support received through grant no. 87/2001–2002 of the Romanian Academy and through Project no. 37/2001 of the Romanian Space Agency, as well as through grant KFKI-CMRC ICA1-CT-2000–70029 and grant HAS-JINR,SANS Project 2002 of the Hungarian Academy of Sciences, is gratefully acknowledged. The opportunities offered by the scientific exchanges between the Romanian Academy and the Hungarian Academy of Sciences are also acknowledged. The authors are indebted to M. Rasa for careful reading of the manuscript.