Non-contact Measurements of Size and Charge Distributions of Submicron Particles using an ESPART Analyzer

Abstract

Characterization of size and electrostatic charge distributions of submicron particles with an instrument capable of in-situ and non-contact measurements is often necessary for many industrial and medical applications. These applications are related to thin film coatings, nanostructural assembly particles for energy conversion research and processing pharmaceutical fine powders, for example. The ESPART analyzer, which is used widely in the electro-photography industries for quality control of toner particles and, recently, in the lung deposition studies of inhaled particles for respiratory drug delivery, operates well in the size range of 1.0 to 20 mum in aerodynamic diameter and for an electrostatic charge range from zero to the saturation charge limit of individual particles with either positive or negative polarity. For measurement of submicron particles, however, several design changes in the instrument are necessary since both optical scattering and electrodynamic properties are significantly different with respect to those of larger particles. Advancement of the ESPART Analyzer with (1) a new optical geometry of Laser Doppler Velocimeter (LDV) for an efficient collection of scattered light from submicron particles, (2) a high frequency simultaneous excitation of the particles, as they cross the sensing volume of the LDV, with acoustic and electric drives and (3) an electronic signal processing system capable of analyzing LDV signals for determining relative phase shift and amplitude of the individual particle motion with respect to the excitation drives is reported. A description of the experimental design is presented. The instrumentation development is supported by a grant from the National Science Foundation.