No Aging Phenomena in Ferrofluids: The Influence of Coating on Interparticle Interactions of Maghemite Nanoparticles

Abstract

The influence of coating on interparticle interactions in ferrofluids has been investigated using various techniques such as Mossbauer spectroscopy, magnetometry, transmission electron microscopy, photon correlation spectroscopy, X-ray diffraction, X-ray photoelectron, and resonance micro-Raman spectroscopy. Aging and spin-glass-like behavior was investigated in frozen ferrofluids of various concentrations from dense, initial value of 40 mg of coated nanoparticles per 1 mL of water, to dilute 1:10 (4 mg/mL). The as-prepared nanoparticles, core size 7-8 nm, were subsequently coated with a gummic acid corona of 20 nm thickness, which was observed to prevent agglomeration and to delay aggregation even in dense ferrofluids. The resulting separation of magnetic cores due to the coating eliminated all magnetic interparticle interaction mechanisms, such as exchange and dipoledipole, thus ensuring no aging effects of the magnetic particle system, as manifested in particle agglomeration and precipitation.

Synthesis and characterization of core–shell type Fe3O4 nanoparticles in poly(organosilsesquioxane)

“…In Fig. 7B, their magnetization curves at 3 K shows a hysteresis curve, 'S'-shaped with non-zero remanence and coercivity, indicating a ferromagnetic behavior It is well known that the magnetic interparticle interactions of magnetic nanoparticles was reduced upon a surface modification [4,5]. The temperature-dependent magnetization of coated nanoparticles in Fig.…”

“…Magnetic nanoparticles (Co, FePt, Gd 2 O 3 , γ -Fe 2 O 3 , Fe 3 O 4 ) consisting of a single magnetic domain in the matrix have shown the superior property in superparamagnetic behavior [1][2][3][4][5], because, there is no magnetization interference between domain wall as in a case of bulk materials. Magnetite nanoparticles (Fe 3 O 4 ) dispersed in solvents are commonly used as ferrofluids and usually prepared by chemical co-precipitation method under aqueous basic condition [6,7].…”

Gummic acid stabilized γ-Fe2O3 aqueous suspensions for biomedical applications

“…The ferrofluids were prepared at high pH and were constantly stirred during this fast one step reaction to avoid the appearance of larger particles. The pH of the final ferrofluid was decreased by carefully numbered titrations of 0.01 M HCl to achieve neutrality followed by dispersion via continuous sonication for 10 min and repetitive filtering of the final colloid though a 0.2 μm porous membrane [5].…”

TEM and Associated Techniques

“…The dispersion is then used to transfer the nanoparticles onto a suitable electrontransparent support grid, and the dispersed specimen must be thoroughly dried before being examined in the TEM [23,24]. Routine specimen analysis typically yields a number of TEM images accompanied by the analytical spectra and/or electron diffraction patterns, as exemplified in Figure 14.1 [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43]. In most cases, the data would suffice for gauging the particle size distribution and uniformity, although it might be difficult to distinguish between the individual nanoparticles in the areas with the overlapping features of interest ( Figure 14.1a).…”