Dipolar magnetism and electrostatic repulsion of colloidal interacting nanoparticle system

Abstract

Thermally activated Brownian kinetics of magnetic nanoparticles in water potentially results in particle aggregation, owing to magnetic and electrostatic interparticle interactions. To determine the significance of those competing interactions in changing the equilibrium hydrodynamic particle volume, we examined the mean distance between polydispersed particles as an important factor for initiating a secondary particle clustering among individually dispersed particles or their primary cluster structures. We particularly characterized the magnetic properties of a superparamagnetic ferrofluid in different ionic environments and at different particle (mass) concentrations. Regarding the concentration of ionic components added to dense ferrofluid samples, the spectral relaxation shift and the reduction in magnetic susceptibility were attributed to different hydrodynamic polydispersities of aggregates. However, no substantial changes in complex susceptibility with increasing ion concentration in dilute ferrofluid samples were confirmed, which indicates relatively stable dipolar-interactions. Regarding the adjustment of particle concentration, we found that the changes in the effective relaxation time constant are proportionally associated with the magnetopotential energy of a given oscillatory magnetic field.

Distributive Activation Volumes of Magnetically Interacting Nanostructures

“…32 Moreover, dispersing the nanoparticles in a liquid medium technically requires surfactants to stabilize the suspension; thus, the coexisting repulsive and attractive interparticle interactions are responsible for defining the equilibrium hydrodynamic polydispersity. 33 To this concern, photon correlation spectroscopy, which has a wide size measurability regardless of magnetic properties, is an effective strategy to quantify the secondary particle size. 34 However, this method may read inaccurate values due to multiple light scattering in the highly concentrated sample.…”

“…In most practices, a nonuniform primary size distribution is an issue in the chemical nanoparticle synthesis, for example, thermal decomposition, coprecipitation, polyol, or solvothermal methods . Moreover, dispersing the nanoparticles in a liquid medium technically requires surfactants to stabilize the suspension; thus, the coexisting repulsive and attractive interparticle interactions are responsible for defining the equilibrium hydrodynamic polydispersity . To this concern, photon correlation spectroscopy, which has a wide size measurability regardless of magnetic properties, is an effective strategy to quantify the secondary particle size .…”

Modelling of the interactions between magnetic nanoparticles in aqueous solutions

“…In this paper, assuming pairwise additivity of interatomic dispersion energies, we will focus on magnetic colloidal particles. Since the model presented here applies to iron oxide nanoparticles with a diameter smaller than 30 nm, it can be assumed that they are uniformly magnetized and single-domain [2,3]. However, due to the magnetic dipole-dipole attractions, aqueous suspensions of magnetic nanoparticles are often not stable and agglomerate quickly [4].…”

Applying SAXS to study the structuring of Fe3O4 magnetic nanoparticles in colloidal suspensions

“…In microscopy techniques, the sample is diluted and dropped in a sample-holder and dried to evaporate the liquid matrix, inducing particle aggregation in a different way than that expected in concentrated suspensions. A better alternative could be Cryo-TEM, in which the sample is quickly frozen using liquid nitrogen, keeping the MNP structuring [5], nevertheless, as with TEM, the sample must be diluted, diminishing the influence of the distancedependent interactions among particles [6][7][8].…”