Measurement of the Effective Density of Both Spherical Aggregated and Ordered Porous Aerosol Particles Using Mobility- and Mass-Analyzers

Online measurement of the effective density of both spherical aggregated and ordered porous particles was systematically investigated using differential mobility analyzer-aerosol particle mass analyzer (DMA-APM). Effective density was determined based on the relationship between electric mobility and mass; mobility and mass were measured using DMA and APM, respectively. The particles were prepared using a spray-drying method; a colloidal suspension of silica nanoparticles was used as the precursor, and both nanoparticles and polystyrene latex (PSL) particles were used to generate the aggregated and ordered porous particles. The effective density of aggregated particles decreased from 1916.0 to 1565.2 kg/m3 when the primary particle size was increased from 6 to 100 nm. The effects of pore size and fraction, which were controlled by PSL particle concentration and size, on the effective density of ordered porous particles were also investigated. The effective density of the ordered porous particles decreased from 922.2 to 682.3 kg/m3 with increasing the porosity from 58.1 to 69.0%, and negligibly affected by individual pore size in a particle. The accuracy of the effective density measurement based on the DMA-APM was greater than 97%. In addition, this method effectively determined particle porosity, as compared by the light-scattering method, with a difference of less than 5% between methods.