Authors: M.L. Eggersdorfer, S.E. Pratsinis
Affilation: ETH Zurich, Switzerland
Pages: 693 - 696
Keywords: nanoparticle agglomerate, fractal dimension, polydispersity, collision mechanism
Agglomeration is encountered in many natural or industrial processes, like growth of aerosol particles in the atmosphere, material synthesis by aerosol processes or even colloidal particles. These particles collide by different mechanisms and stick together forming irregular or fractal-like agglomerates. Typically, the structure of these agglomerates is characterized with the fractal dimension, Df, and pre-exponential factor, kn, of simulated agglomerates of monodisperse primary particles (PP) for ballistic or diffusion-limited particle-cluster and cluster-cluster collision mechanisms. This concept has served well a wide spectrum of aerosol-made particles, in particular by coagulation. In fact, process design concepts have been developed capitalizing on these Df values to extract other particle properties and design reactors for manufacturing such particles. What might have been overlooked in characterization and simulations of such particles is that the above Df values have been developed for agglomerates of monodisperse primary particles. Here, the effect of PP polydispersity on Df and kn is investigated with agglomerates consisting of 16 – 1024 PP with closely controlled size distribution. Broadening the PP size distribution of agglomerates decreases monotonically their Df. So Df can be an indication for PP polydispersity in mass–mobility and light scattering measurements.