Direct Imaging of Zero-Field Dipolar Structures in Colloidal Dispersions of Synthetic Magnetite

Abstract

Magnetite (Fe3O4) forms the basis of most dispersions studied in the field of magnetic fluids and magnetic colloids. Despite extensive theory and simulations on chain formation in dipolar fluids in zero field, such structures have not yet been imaged in laboratory-made magnetite dispersions. Here, we present the first direct observation of dipolar chain formation in zero field in a ferrofluid containing the largest synthetic single-domain magnetite particles studied so far. To our knowledge, this is the only ferrofluid system available at present that allows quantifying chain length and ring-size distributions of dipolar structures as a function of concentration and particle size.

Surface analysis of magnetite nanoparticles in cyclohexane solutions of oleic acid and oleylamine

“…1). Line broadening in X-ray diffraction patterns agrees with the particle diameter obtained from TEM, indicating that the particles are single crystals [5]. The magnetic diameter (6.0 nm) calculated from magnetization curves agrees with the physical diameter [14], indicating that the particles have a single magnetic domain [5].…”

“…A sterically stabilized colloidal dispersion of magnetite nanoparticles in cyclohexane was prepared according to a procedure previously described [4,5]. In this procedure, magnetite nanoparticles are synthesized in 20 mL phenyl ether by reduction of iron(III) acetylacetonate using 1,2-hexadecanediol.…”

“…Subsequently, the supernatant is removed and the particles are again dispersed in 20 mL phenyl ether to repeat the above www.elsevier.com/locate/vibspec Vibrational Spectroscopy 43 (2007) [243][244][245][246][247][248] described synthesis procedure twice. In this way, the average particle size is increased by the seeded growth of the particles prepared in the first step and the polydispersity is reduced from 33% to 11% [5]. After the last growth step, the supernatant is removed and the precipitated magnetite is dissolved in 5 mL cyclohexane.…”

“…A much-used surfactant for magnetic nanoparticles in non-aqueous ferrofluids is oleic acid [1], but recently the equimolar combination of oleic acid with oleylamine has been advocated [2][3][4]. Oleylamine affects the synthesis of nanoparticles of various materials, including FePt [2], FeMo [3], and magnetite (Fe 3 O 4 ) [3,5], although the mechanism remains unclear. Moreover, surfactant desorption is expected to take place during the chemical purification steps at the end of the synthesis, but few studies mention quantitative information about this problem [6,7].…”

Dipolar Structures in Colloidal Dispersions of PbSe and CdSe Quantum Dots

“…The imaged structures strongly resemble the magnetic dipolar structures that have been observed recently in colloidal iron and magnetite dispersions. 13,14 As a first quantification of the imaged dipolar structures, we calculated the radial distribution function g(r), defined as:…”