NMR studies into colloidal stability and magnetic order in fatty acid stabilised aqueous magnetic fluids

Abstract

We report the physico-chemical characterisation of fatty acid stabilised aqueous magnetic fluids, which are ideal systems for studying the influence of nanoparticle aggregation on the emergent magnetic resonance properties of the suspensions. Stable colloids of superparamagnetic magnetite, Fe(3)O(4), nanoparticle clusters in the 80 to 100 nm size range were produced by in situ nanoparticle growth and stabilisation, and by suspending pre-formed nanoparticles. NMR relaxation analysis shows that the magnetic resonance properties of the two types of suspension differ substantially and provides new insights into how the relaxation mechanisms are determined by the organisation of the nanoparticles within the clusters.

Epoxy Ring Opening Phase Transfer as a General Route to Water Dispersible Superparamagnetic Fe3O4 Nanoparticles and Their Application as Positive MRI Contrast Agents

“…This technique involves measurement of r 1 as a function of field strength, and hence 1 H Larmor frequency. NMRD is well established for the analysis of MNP suspensions 14, 28, 29. Its advantage over fixed‐field measurements is that it provides insights into the dynamics of the magnetic moments and into the magnetic order of the particles (as sensed by the solvent molecules) 30.…”

“…Phase transfer by encapsulation has been demonstrated using amphiphilic molecules such as fatty acids,10 DTAB,11 and PMAO‐PEG12 polymer producing bilayer‐stabilized MNPs. The surface chemistry is such that the resulting layers are not always stable, e.g., to dilution,13, 14 or in the presence of phosphate buffer. Encapsulation of MNPs with a range of polymers, both without15, 16 and with17, 18 subsequent cross‐linking (to promote stability of the outer layer) has also been noted.…”

Magnetic, X-ray and Mössbauer studies on magnetite/maghemite core–shell nanostructures fabricated through an aqueous route

“…Néel relaxation of superparamagnetic Fe 3 O 4 is an effective way to heat up the nanocrystals and the surrounding tissue by transferring energy from the external magnetic eld in therapeutic hyperthermia and, more recently, in the development of theranostic technologies. 1,17 Large surface area to volume ratio for nanoparticles provides enormous driving force for diffusion, especially at elevated temperatures. 18 Colombo et al calculated the activation energy for the reduction of iron oxides (hematite, maghemite and magnetite) at 150 to 400 C under reductive atmosphere.…”

Monodisperse magnetic nanoparticle assemblies prepared at scale by competitive stabiliser desorption

“…Methods used to produce magnetic NPCs usually rely on the use of expensive, high molecular weight polymers. This is the case for the in situ NP synthesis/assembly [5,6], for micellar approaches [7][8][9] and for polymer mediated phase transfer/encapsulation [10,11]. Alternative approaches based on low molecular weight surface active materials typically result in little control over the cluster size and often of moderate colloidal stability [12].…”