Effect of surface change by vacuum drying on the sedimentation stability of iron nanoparticles in volatile organic solvents

Sedimentation stability of iron nanoparticles (FeNPs) in low viscosity, volatile organic solvents such as ethanol and MEK is crucial for the high-quality production of FeNP-based electronics. Adding dispersants represents nowadays the common strategy to improve the sedimentation stability of FeNPs, but suffers from toxicity and high costs. Here, we present a simple vacuum drying process for enhancing the sedimentation stability of FeNPs in ethanol without using dispersants. In-situ light transmission and scattering detection showed that vacuum-dried FeNPs in ethanol and MEK sedimented much slower than those of non-treated FeNPs. The cause for the enhanced sedimentation stability was explained by Stoke's law and inter-particle attraction force change due to the reduced hydroxyl groups by the vacuum annealing. A systematic analysis of the FeNP surfaces before and after annealing provided a detailed picture of the advantages to carry out a simple vacuum annealing process to improve sedimentation stability.