Hollow magnetic microspheres obtained by nanoparticle adsorption on surfactant stabilized microbubbles

Abstract

We report on the stabilization of nanoparticle-decorated microbubbles for long periods of time using a synergism between a soluble surfactant and nanoparticles. The soluble surfactant is the perfluoroalkyl phosphate C₈F₁₇(CH₂)₂OP(O)(OH)₂ (labeled F8H2Phos) and the nanoparticles (NPs) are 20–25 nm cobalt ferrite (CoFe₂O₄). The NP–F8H2Phos system has been studied by dynamic light scattering, dynamic magnetic susceptibility measurements and thermal gravimetric analysis. Microbubbles with diameters in the 1–20 μm range have been stabilized in 0.1 M NaCl brine. Its presence is crucial for the long-term stabilization. The surfactant adsorbs rapidly on bubbles and slows down the bubble shrinkage. Thus, the NPs can attach to the bubble and form a hollow sphere with a rigid shell. The charge screening by NaCl favors the attachment of NPs to the bubble surface. The coverage of the bubbles by the CoFe₂O₄ nanoparticle layer is confirmed by thermally induced inflation–deflation experiments and the control of bubbles with a magnetic field.