Details

Autor(en) / Beteiligte

• Vasilescu, Corina
• Latikka, M
• Knudsen, K. D
• Garamus, V. M
• Socoliuc, V
• Turcu, Rodica
• Tombácz, Etelka
• Susan-Resiga, Daniela
• Ras, R. H. A
• Vékás, L

Titel

High concentration aqueous magnetic fluids: structure, colloidal stability, magnetic and flow propertiesElectronic supplementary information (ESI) available: Fig. S1. ATR-FTIR spectra measured from dried solutions of the electrostatically stabilized magnetic fluid, uncoated iron oxide nanoparticles and citric acid. The pH of the MF/CA sample was ∼7 and that of the reference samples was adjusted to ∼7. Fig. S2. ATR-FTIR spectra measured from dried solutions of the electro-sterically stabilized ma

Erscheinungsjahr

2018-08

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• This paper is an in-depth analysis devoted to two basic types of water based magnetic fluids (MFs), containing magnetite nanoparticles with electrostatic and with electro-steric stabilization, both obtained by chemical coprecipitation synthesis under atmospheric conditions. The two sets of magnetic fluid samples, one with citric acid (MF/CA) and the other with oleic acid (MF/OA) coated magnetic nanoparticles, respectively, achieved saturation magnetization values of 78.20 kA m −1 for the electrostatically and 48.73 kA m −1 for the electro-sterically stabilized aqueous ferrofluids which are among the highest reported to date. A comprehensive comparative analysis combining electron microscopy, X-ray photoelectron spectroscopy, attenuated total reflectance Fourier transform infrared spectroscopy, vibrating sample magnetometry, small-angle X-ray and neutron scattering, dynamic light scattering and magneto-rheometry revealed similarities and essential differences on the microscopic and macroscopic level between the two kinds of water-based ferrofluids. While the saturation magnetization values are quite different, the hydrodynamic volume fractions of the highest concentration MF/CA and MF/OA samples are practically the same, due to the significantly different thicknesses of the particles' coating layers. The results of volume fraction dependent structure analyses over a large concentration range by small-angle X-ray and neutron scattering, correlated with magneto-rheological investigations for the electrostatically stabilized MFs, demonstrate formation of short chains of magnetic nanoparticles which are relatively stable against coagulation with increasing concentration, while for MFs with electro-steric stabilization, magnetic field and shear rate dependent loosely bound structures are observed. These particle structures in MF/OA samples manifest themselves already at low volume fraction values, which can be attributed mainly to magnetic interactions of larger size particles, besides non-magnetic interactions mediated by excess surfactant. This paper is an in-depth analysis devoted to two basic types of water-based magnetic fluids (MFs), containing magnetite nanoparticles with electrostatic (a) and with electro-steric (b) stabilization, both obtained by chemical coprecipitation synthesis under atmospheric conditions.