AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
Online Particle Separation and Shape Measurement Using Pulsed-Field DMA
MINGDONG LI, George Mulholland, Michael Zachariah, University of Maryland
Abstract Number: 154 Working Group: Instrumentation and Methods
Abstract One of the major challenges in particle measurement is to extend the dimensionality measurement beyond the assumption of spherical symmetry. For a nonspherical particle, a standard differential mobility analyzer (DMA) measurement yields a mobility-equivalent spherical diameter, but provides no information about the degree of sphericity. However, given that the electrical mobility for nonspheres is orientation-dependent, and that orientation can be manipulated using electric fields of varying strength, one can, in principle, extract shape information through a systematic measurement of mobility as a function of particle orientation. Here, we describe the development of a pulsed-field differential mobility analyzer (PFDMA) which enables one to change the peak E-field experienced by the particle to induce orientation, while still maintaining the same particle transit time. The instrument is validated with polystyrene latex (PSL) spheres with accurately known size, and gold rods with dimensions accurately determined by transmission electron microscopy (TEM). We demonstrate how the instrument can be used for particle separation and extraction of shape information. In particular, we show how one can extract both length and diameter information for rod-like particles.
The most important class of non-spherical particles are aggregates. Recently, we have demonstrated how this instrument can be applied to aggregates, and demonstrate that the mobility size of soot non-spherical aggregates showed a clear alignment effect. Since the mobility size of spheres is constant, the experimental results demonstrate that PFDMA could be used to separate spherical particles from non-spherical aggregates. This generic approach can be used to obtain shape information for nonsphercial particles and separate particles based on their shape.