Production of monodispersed particles by using effective size selection

Abstract

In this article we report the results of two size selection methods that are based on interfacial interaction between nanosize particles, magnetite in this case, anionic surfactants, and nonpolar solvents. It is proposed that by selecting a suitable surfactant type and/or conditions to modify the particle–particle separation distance, only smaller particles can be stabilized against aggregation and settling making a size sensitive separation possible. Using this phenomenon, an effective size selection at the nanosize level has been achieved and the preliminary results are presented here. Depending on the conditions, stable suspensions of nearly monodispersed nanoparticles of magnetite (diameter less than 10 nm and standard deviation, σ, below 0.2) were obtained from polydispersed powders (less than 40 nm in diameter and σ around 0.6) synthesized from aqueous solutions at 25 °C. Magnetization measurements of the fractions confirmed the effectiveness of the developed size selection methods.

Enhanced Chemical Ordering and Coercivity in FePt Alloy Nanoparticles by Sb‐Doping

“…Asprepared 8.5 nm FePt nanoparticles with high Sb content (e.g., X Sb~0 .23) contain partially L1 0 -ordered structure yielding a room-temperature value of H c~1 20 mT. Though the as-synthesized nanoparticles have a relatively broad size distribution, we envision that combining Sb-doping with appropriate size-selection techniques [25] may help realize more-ordered nanoparticle assemblies. The ordering temperature bears an inverse correlation with Sb activity, and can be lowered by~50±100 C more than the lowest reported for Ag-or Au-doped FePt nanoparticles.…”

“…[17,18] However, we find that assembly ordering can be improved by narrowing the particle size distribution by adopting appropriate size-selection methods. [25] For example, diluting the nanoparticle solution and then taking the supernatant after a suitable settling time [25] leads to lower variation in size and enhances particle packing (Figs. 1b,c).…”

Tuning of magnetic properties in cobalt ferrite nanocrystals

“…3 It is known that the crystal size is related to the relative interdependence between the nucleation and growth steps, which, in turn, can strongly be affected by the solution chemistry and precipitation conditions. [4][5][6] Several synthesis methods have been employed to control particle size and shape, ion distribution, structure and hence, the magnetic properties of ferrites. [7][8][9][10] Related literature was focused on the synthesis of cobalt ferrite in the superparamagnetic region ͑where no significant enhancement of coercivity is possible͒ 3,8,[10][11][12] or polycrystalline multidomain particles, 13,14 in which case coercivity is expected to decrease.…”

Synthesis and Magnetic Properties of Cobalt Ferrite With Different Morphologies

“…[1][2][3][4][5] Amongst the several ferrite materials, cobalt ferrite (CoFe 2 O 4 ) has been widely considered because it retains excellent chemical stability and good mechanical hardness [6] . In addition to the detailed control on the composition and structure of CoFe 2 O 4 , the achievement of its practical application depends on the ability of controlling surface morphology with crystallite size within nanometer range [7][8][9] . The morphology and crystallite size are related to the relative interdependence among the nucleation and growth steps, which in turn can intensely be affected by the solution chemistry and precipitation conditions [10][11][12] .…”