Field induced phase segregation in ferrofluids

We study the phase segregation in magnetite ferrofluids under the influence of an external magnetic field. A phase with lower nanoparticle density and corresponding higher optical transmission is formed in the bottom of a glass cell in the presence of only a very modest magnetic field gradient (smaller than 25 T/m25 T/m). The flux density in our magnetic configuration is simulated using finite element methods. Upon switching off the external magnetic field, the low-density phase develops into a ‘bubble’-like feature. The kinetics of this ‘bubble’ in the absence and presence of a magnetic field are described and analyzed in terms of a simple model, which takes into account buoyancy and drag forces.

Graphical abstractField-induced phase segregation in magnetite ferrofluid, as observed by video imaging, showing the formation of a low density ‘bubble’. The ‘bubble’ height increases continuously with time due to buoyancy.Figure optionsDownload full-size imageDownload as PowerPoint slide