Abstract View
Tuning Nanoparticle Aggregation with Externally Applied Magnetic Field Strength
PRITHWISH BISWAS, Pankaj Ghildiyal, George Mulholland, Michael Zachariah, University of California, Riverside
Abstract Number: 558
Working Group: Aerosol Physics
Abstract
Assemblies of metal nanoparticles occurring during aerosol routes of synthesis often limits their applications. Due to weak inter particle Hamaker type interaction forces, fast Brownian motion limits the aggregation of metal nanoparticles, a phenomenon, popularly known as diffusion limited cluster aggregation (DLCA). Nanoparticle aggregates formed by DLCA has a universal fractal dimension of ~1.8, which is undesirable, as this type of aggregation greatly reduce the effective surface area. However, in the case of magnetic nanoparticles, an external magnetic field can be used to tune the fractal dimension of the aggregates formed. The presence of a magnetic field induces attractive interaction forces between two magnetic particles only along the direction of the magnetic field, whereas repulsive interaction forces are induced along all other directions. A canonical ensemble Monte Carlo simulation has been performed for a system of spherical particles interacting with each other through a directional magnetic potential, to study the effect of the directional magnetic field in tuning the aggregate shape. The pair distribution function between the particles and the radius of gyration of the aggregates have been evaluated to estimate the fractal dimensions, both of which follow a scaling law with the aggregate size. It has been observed that the fractal dimensions of the aggregates decreases with the increase in the strength of potential and reaches a saturation at ~1.17. The particles also show a tendency to get aligned along the direction of the magnetic field forming linear chain aggregates, as the strength of the magnetic field is increased. These linear aggregates are desirable in making high density composites for various applications and the strength of the magnetic field required for this transition in the shape of the aggregates is practically achievable. Hence, this study will be useful in designing nanoparticle synthesis procedures with controlled aggregation.