AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Prediction of the Alignment, Preferred Orientation and Electrical Mobility of Nanoparticle Agglomerates during Electrical Mobility Classification
RANGANATHAN GOPALAKRISHNAN, University of Iowa
Abstract Number: 536 Working Group: Aerosol Physics
Abstract Non-spherical Nanoparticles (NPs) such as agglomerates experience an electrical force as well as a net torque about their center of rotation when they move in electric fields. To separate such particles by their size and shape, Differential Mobility Analyzers (DMAs) are operated at field strengths that are high enough to induce various degrees of alignment with the electric lines of force due to the competition between random thermal rotational motion (Brownian diffusion) and dielectrophoresis induced by polarization forces. By using exact relationships between particle shape and the potential energy of polarization, Fuchs has predicted the average orientation of prolate and oblate spheroids in electric fields. Following Fuchs’ approach and by using accurate computations of the polarization energy of agglomerates of arbitrary shape (number, position and size of primary spheres), the propensity of such particles to align in the presence of electric fields is predicted here. Further, the orientation averaged mobility is computed for each shape by combining the mobility of a particle at a specific orientation and the orientation probability distribution. Calculations are presented for dimers, linear chains of tangential spheres as well as fractal aggregates of practical importance. The results presented here enable reconciliation of observed electrical mobilities with shape parameters of agglomerated particles at various operating field strengths used in DMAs.