The Centrifugal Differential Mobility Analyser – A new device for determination of two-dimensional property distributions

Abstract. Usually, for the characterisation of nanoparticles an equivalent property is measured, e.g. the mobility equivalent diameter. In the case of non-spherical, complex shaped nanoparticles, one equivalent particle size is not sufficient for a complete characterisation. Most of the methods utilised to gain deeper insight into the morphology of nanoparticles are very time consuming and costly or have bad statistics (such as tandem-setups or SEM/TEM images). To overcome these disadvantages, a prototype of a new compact device, the Centrifugal Differential Mobility Analyser, the CDMA, was built, which can measure the full two-dimensional distribution of mobility and stokes equivalent diameters by classification in a cylinder gap, through electrical and centrifugal forces. An evaluation method to determine the transfer probabilities is developed and used in this work to compare the measurement results with the theory for the pure rotational behaviour (like the Aerodynamic Aerosol Classifier) and the pure electrical behaviour (like the Dynamic Mobility Analyser). In addition, the ideal two-dimensional transfer function was derived using a particle trajectory approach. This two-dimensional transfer function is a prerequisite for obtaining the full two-dimensional particle size distribution from measurements by inversion.