Self-Assembly of Polymer-Magnetite Nanoparticles under the Influence of an External Magnetic Field
F. Marco, L. Marco, M. Massimo
ETH Zurich, CH
Keywords: magnetic nanoparticles, self-assembly, gels, porour materials, controlled structure
Abstract:For this work, magnetic nanoparticles, composed of magnetite nanocrystals dispersed into a polymer matrix, have been prepared via miniemulsion polymerization. Due to the superparamagnetic behavior of the nanocrystals embedded in the polymer matrix, the nanoparticles prepared in this manner, which have an average size below 100nm, develop strong and reversible dipolar interactions only in the presence of an external magnetic field. We have then studied the self-assembly and gelation behavior of dispersions of these nanoparticles in presence and absence of an external magnetic field. The nanoparticels, which are stabilized by means of electrostatic interactions, are partially destabilized by adding controlled amount of electrolytes. In the absence of magnetic fields, the particles self-assemble into random fractal clusters, which eventually percolated to form a gel, if the volume fraction of the particles is sufficiently high. Instead, when an external magnetic field is applied, the particles align themselves in columnar structure. If the external magnetic field is applied when the gelation process has already begun, both particles and clusters are aligned in the direction of the magnetic field. By tuning the time at which the field is applied, different structures and characteristic pore sizes in the gel are obtained.