Mass-production of water-based ferrofluids capable of developing spike-like structures

Abstract

Ferrofluids are among the most popular and engaging materials related to the nanotechnology field, with applications ranging from studies of basic science phenomena to educational and outreach activities. Therefore, there is a continuous interest in the synthesis strategies used to fabricate these systems, especially those that can lead to simple procedures able to be reproduced under a wide spectrum of laboratory conditions. The ferrofluids described in this work are systems composed of iron oxide nanoparticles synthesized by the coprecipitation method and functionalized with citrate molecules to ensure the dispersion in an aqueous medium. During the experimental work we evaluated different operations and synthesis conditions, in order to arrive to a unique procedure that optimizes the functionalization results and the scaling potential. The optimized synthesis route has two main features that are worth to highlight. The first is the possibility of using readily available commercial products as chemical precursors; the second is the overall reduction of the procedure difficulties, as we show that several operations that are usually used in similar reports can be avoided, such as sonication, centrifugation, dialysis, inert atmospheres of Ar/N2 or heating of large volumes of liquid. Both features can be included in the synthesis route without compromising the ferrofluid quality. The procedure can be used to successfully prepare nearly 30 g of functionalized nanoparticles per synthesis batch. Furthermore, this production has the potential to increase due to the absence of significant limitations in the scaling process. We show that the synthesized nanoparticles can produce a stable colloid even at extremely high concentrations (above 50% wt), leading to the formation of ferrofluids that can develop static peak patterns, known as Rosensweig instabilities, when exposed to an external magnetic field. In turn, we show that the extent of these disturbances can be modified both with the concentration of nanoparticles and with the surface tension of the ferrofluid, as expected for this type of system.