Ferrofluid field induced flow for microfluidic applications

Exposing a column of ferrofluid to coincident magnetic and thermal fields produces a pressure gradient in the magnetic fluid. As the column of ferrofluid heats up, it loses its attraction to the magnetic field and is displaced by cooler fluid. Subsequently, it is possible to generate a ferrofluid pump with no moving mechanical parts. Until recently, limitations in the magnetic and thermal properties of conventional materials severely limited operating pressures. Advancements in the design and synthesis of metal substituted magnetite enable fine control over both the magnetic and thermal properties of magnetic nanoparticles, a key element in ferrofluids. This manuscript covers three recent contributions to the design of ferrofluid pumps. First, we introduce a new approach to the synthesis of metal substituted magnetite nanoparticles based on thermophilic metal-reducing bacteria. Next, we extend the previous work in the modeling of the ferrofluid pumps to include the coupling between each of the three fundamental domains: magnetic, thermal and fluid dynamic. We validate these models with a comparison between experimental results and a multidomain finite element model. Our results show a good match between the model and experiment as well as approximately an order of magnitude increase in the fluid flow rate over conventional magnetite based ferrofluids operating below 80°C. Finally, as a practical demonstration, we describe a novel application of this technology: pumping fluids at the microfluidic scale.