Abstract
We present a Discrete Element study of the behavior of magnetic core-shell particles in which the properties of the core and the shell are explicitly defined. Particle cores were considered to be made of pure iron and thus possessed ferromagnetic properties, while particle shells were considered to be made of silica. Core sizes ranged between 0.5 and 4.0 μm with the actual particle size of the core-shell particles in the range between 0.6 and 21 μm. The magnetic cores were considered to have a magnetization of one tenth of the saturation magnetization of iron. This study aimed to understand how the thickness of the shell hinders the formation of particle chains. Chain formation was studied with different shell thicknesses and particle sizes in the presence and absence of an electrical double layer force in order to investigate the effect of surface charge density on the magnetic core-shell particle interactions. For core sizes of 0.5 and 4.0 μm the relative shell thicknesses needed to hinder the aggregation process were approximately 0.4 and 0.6 respectively, indicating that larger core sizes are detrimental to be used in applications in which no flocculation is needed. In addition, the presence of an electrical double layer, for values of surface charge density of less than 20 mC/m2, could stop the contact between particles without hindering their vertical alignment. Only when the shell thickness was considerably larger, was the electrical double layer able to contribute to the full disruption of the magnetic flocculation process.
Highlights
Core-shell particles are particles whose cores are made of different component materials to those of the shell surrounding them (Cao et al, 2009; Mora-Huertas et al, 2010)
The focus of this paper was to investigate the influence of the shell thickness of magnetic core-silica shell particles on their colloidal stability, for different values of surface charge density
Computer simulations based on the Discrete Element Method have been carried out to study the influence of shell thickness of magnetic core-silica shell particles
Summary
Core-shell particles are particles whose cores are made of different component materials to those of the shell surrounding them (Cao et al, 2009; Mora-Huertas et al, 2010). There is an inorganic or organic particle core which is surrounded by a layer or multilayer of a different inorganic or organic material These core-shell particles have the advantage of possessing properties of both the core and its surrounding shell. This gives benefits in terms of improving the stability and surface chemistry of the core particle and gives unique physical and chemical properties that are impossible to have if only one type of material is used (Caruso et al, 1999; Cao et al, 2009). The shell could be a soft layer of attached molecules, such as functional polymers which can be used to tune the specific surface interactions
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