Volume Measurement and Processing of Metal Nanoparticles in the Aerosol Phase

CYPRIEN JOURDAIN, Jonathan Symonds, Adam M Boies, University of Cambridge

     Abstract Number: 479
     Working Group: Instrumentation and Methods

Abstract
Particles in the aerosol phase are largely non spherical and can exhibit complex morphologies such as agglomerates of multiple primary particles or powders with significant porosity. Determining the volume of such nanoparticles remains challenging. Volume is a crucial property as it impacts the ability of particles to conduct heat, to shape their internal electric field, and because it relates the particle true mass to its effective density. Traditionally, mass-mobility measurements are used to determine particle effective density and allow to indirectly infer the volume from a mass measurement. An alternative methodology is proposed in this work to measure the volume of nanoparticles in near real time.

The operation principle is to force electrostatic particle-droplet interaction/coagulation and to measure the changes in volume associated with the particle encapsulation. Solid particles are synthesized at high temperature (soot, metal) or dispersed (PSL, powders) and positively charged, while simultaneously, oil droplets are atomized and negatively charged. Both populations are then mobility selected and mixed in a chamber. Following the removal of charged particles, the mobility and aerodynamic diameters of the encapsulated (neutral) particles are measured, allowing the determination of the volume and the effective density.

The preliminary results show that for silver aggregates encapsulated in DEHS, linear relationships exist between the aerodynamic diameter shift and the initial mobility diameter of the silver particle (d_mp), given a known droplet size. The mass of the combined droplet had a 6-fold increase for the largest d_mp (90 nm). Aggregate volumes in the order of 10⁵ nm³ were found using a single droplet size (d_md = 150 nm) and aggregates with d_mp ranging from 30 to 90 nm. Building on these promising results, a range of particle-droplet size combinations will be tested, along with different liquid and solid materials, the latter likely to exhibit internal structures.