(189al) Agglomerate Formation with Polydisperse Primary Particles in the Transition Regime

During flame synthesis of nanoparticles, polydisperse primary particles (PPs) are formed by surface growth¹ and/or coalescence.² At high temperatures, PPs coagulate in the free molecular regime producing fractal-like agglomerates.³ When these agglomerates exit the high-temperature region of flame reactors or enter high-pressure environments (e.g. in combustion engines), they coagulate in the transition regime as their mean free path becomes comparable to their size.⁴ Agglomeration dynamics at these conditions depend on the spread of the PP size distribution.

Here, an Event-Driven (ED) model for agglomeration of polydisperse PPs is employed to investigate the evolution of agglomerate structure and size distribution from free molecular to transition regime. The broad agglomerate size distributions formed in the free molecular regime narrow by coagulation in the transition regime, attaining their quasi-Self-Preserving Size Distribution (SPSD) with gyration- and mobility-based geometric standard deviations of 1.62 ± 0.03 and 1.48 ± 0.03, respectively, regardless of PP polydispersity. Agglomeration results in a self-preserving scaling law between the mobility diameter, d_m, and the number of constituent PPs within an agglomerate, n_p. The ED-derived quasi-SPSD of the agglomerate d_m and its self-preserving scaling to n_p are in excellent agreement with mass-mobility measurements of soot and zirconia agglomerates and can be interfaced with method of moments or population balance models to assist the design of aerosol flame reactors and combustion engines.

References:

[1] Kelesidis, G. A.; Goudeli, E.; Pratsinis, S. E., Flame synthesis of functional nanostructured materials and devices: Surface growth and aggregation. Proc Combust Inst 2017, 36, 29-50.

[2] Eggersdorfer, M.L.; Kadau, D.; Herrmann, H.J.; Pratsinis, S.E., Multiparticle Sintering Dynamics: From Fractal-Like Aggregates to Compact Structures. Langmuir 2011, 27, 6358-6367.

[3] Goudeli, E.; Eggersdorfer, M.L.; Pratsinis, S.E., Coagulation of Agglomerates Consisting of Polydisperse Primary Particles. Langmuir 2016, 32, 9276-9285.

[4] Kelesidis, G. A.; Goudeli, E.; Pratsinis, S. E., Morphology and mobility diameter of carbonaceous aerosols during agglomeration and surface growth. Carbon 2017, 121, 527-535.