(285g) Impact of Humidity on Silica Nanoparticle Agglomerate Morphology and Size Distribution

Fractal-like agglomerates of physically-bonded single primary particles (PPs) and/or chemically-bonded ones (aggregates) are typically formed by agglomeration during flame synthesis.¹ This ramified agglomerate morphology changes drastically during atmospheric aging,² storage or industrial processing by spray granulation³ or fluidization⁴ in the presence of humidity.

Here, flame-made agglomerates of silica nanoparticles are humidified at various saturation ratios and dried before characterization with an aerosol diagnostic set up.⁵ These agglomerates collapse into compact structures and follow a fractal scaling law after humidification followed by drying. The hydrophilic surface of silica delays water evaporation and results in a critical saturation ratio larger than that of hydrophobic particles (e.g. soot²). Online diagnostics using a scaling law derived here from first principles are employed to monitor for the first time the aggregate size and its impact on agglomerate morphology after condensation-evaporation. The humidified-dried silica agglomerates are more porous compared to those of soot² due to their larger aggregate size. The method developed here can facilitate handling, storage, processing and eventual performance of spray-dried³ and fluidized nanoparticle granules⁴ in different applications, such as batteries and fuel cells.

References:

[1] 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.

[2] Ma, X. F.; Zangmeister, C. D.; Gigault, J.; Mulholland, G. W.; Zachariah, M. R., Soot aggregate restructuring during water processing. J Aerosol Sci 2013, 66, 209-219.

[3] Kim, J.; Wilhelm, O.; Pratsinis, S. E., Nanoparticle packaging. Adv Eng Mater 2002, 4, 494-496.

[4] Fabre, A.; Steur, T.; Bouwman, W. G.; Kreutzer, M. T.; van Ommen, J. R., Characterization of the Stratified Morphology of Nanoparticle Agglomerates. J Phys Chem C 2016, 120, 20446-20453.

[5] Goudeli, E.; Gröhn, A. J.; Pratsinis, S. E., Sampling and dilution of nanoparticles at high temperature. Aerosol Sci Technol 2016, 50, 591-604.