Abstract View
On-the-fly Directed Assembly of Metal Nanoparticles from Electromagnetically Levitated Metal Droplets
PANKAJ GHILDIYAL, Prithwish Biswas, Steven Herrera, Reza Abbaschian, Michael Zachariah, University of California, Riverside
Abstract Number: 555
Working Group: Nanoparticles and Materials Synthesis
Abstract
Aerosol-synthesis techniques offer a scalable approach to production of metal nanoparticles and their assembly into well-defined structures. Fast particle diffusion rates in gaseous media typically cause rapid and uncontrollable, random aggregation, thus limiting controlled, directed assembly of nanoparticles in the aerosol phase. One approach to achieve directionality and control of nanoparticle assembly in the gas phase would be to employ an external magnetic field during particle formation and aggregation such that the directional interactions of the nanoparticles with the field compete with random, Brownian coagulation.
In this work, we explore an electromagnetic levitation technique to generate metal nanoparticles and tune their aggregate structure and morphology. This technique employs an electromagnetic levitation coil that levitates and inductively heat bulk metal pieces (~1cm) beyond their melting points. High temperatures (up to 2500K) and large evaporative flux achieved at the droplet surface result in a large supersaturation of metal atoms around the droplet, leading to nucleation and growth of metal nanoparticles that are transported and collected downstream by an inert carrier gas. Levitation allows the reactor to be wall-less and crucible-free and prevents crucible contamination at elevated temperatures. In addition, the magnetic field arising from the induction coil may also have a directional effect on the assembly and aggregate structure, particularly for magnetic metal nanoparticles. Morphologically distinct aggregates are obtained depending on the magnetic properties of the metal used. Aggregates from ferromagnetic metals such as Fe and Ni appear to be ‘stringier’ and chain-like (lower fractal dimension, Df), while for paramagnetic Cu, a more compact structure with a higher Df value is obtained. Thus, this technique offers a scalable, aerosol-phase approach to generate structurally distinct aggregate assemblies of metal nanoparticles.