Agglomerate settling impacts nanotoxicology and nanomedicine as well as the stability of engineered nanofluids. Here, the mobility of nanostructured fractal-like SiO2 agglomerates in water is investigated and their settling rate in infinitely dilute suspensions is calculated by a Brownian dynamics algorithm tracking the agglomerate translational and rotational motion. The corresponding friction matrices are obtained using the HYDRO++ algorithm [J. G. de la Torre, G. del Rio Echenique, and A. Ortega, J. Phys. Chem. B 111, 955 (2007)] from the Kirkwood-Riseman theory accounting for hydrodynamic interactions of primary particles (PPs) through the Rotne-Prager-Yamakawa tensor, properly modified for polydisperse PPs. Agglomerates are generated by an event-driven method and have constant mass fractal dimension but varying PP size distribution, mass, and relative shape anisotropy. The calculated diffusion coefficient from HYDRO++ is used to obtain the agglomerate mobility diameter dm and is compared with that from scaling laws for fractal-like agglomerates. The ratio dm/dg of the mobility diameter to the gyration diameter of the agglomerate decreases with increasing relative shape anisotropy. For constant dm and mean dp, the agglomerate settling rate, us, increases with increasing PP geometric standard deviation σp,g (polydispersity). A linear relationship between us and agglomerate mass to dm ratio, m/dm, is revealed and attributed to the fast Brownian rotation of such small and light nanoparticle agglomerates. An analytical expression for the us of agglomerates consisting of polydisperse PPs is then derived, (ρf is the density of the fluid, ρp is the density of PPs, μ is the viscosity of the fluid, and g is the acceleration of gravity), valid for agglomerates for which the characteristic rotational time is considerably shorter than their settling time. Our calculations demonstrate that the commonly made assumption of monodisperse PPs underestimates us by a fraction depending on σp,g and agglomerate mass mobility exponent. Simulations are in excellent agreement with deposition rate measurements of fumed SiO2 agglomerates in water.
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14 February 2018
Research Article|
February 09 2018
Mobility and settling rate of agglomerates of polydisperse nanoparticles
Anastasia Spyrogianni;
Anastasia Spyrogianni
a)
1
Department of Mechanical and Process Engineering, ETH Zurich
, Zurich 8092, Switzerland
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Katerina S. Karadima
;
Katerina S. Karadima
a)
2
Department of Chemical Engineering, University of Patras
, Patras 26504, Greece
3
Institute of Chemical Engineering Sciences, FORTH/ICE-HT
, Patras 26504, Greece
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Eirini Goudeli;
Eirini Goudeli
4
Department of Mechanical Engineering, University of Minnesota
, Minneapolis, Minnesota 55455, USA
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Vlasis G. Mavrantzas
;
Vlasis G. Mavrantzas
b)
1
Department of Mechanical and Process Engineering, ETH Zurich
, Zurich 8092, Switzerland
2
Department of Chemical Engineering, University of Patras
, Patras 26504, Greece
3
Institute of Chemical Engineering Sciences, FORTH/ICE-HT
, Patras 26504, Greece
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Sotiris E. Pratsinis
Sotiris E. Pratsinis
b)
1
Department of Mechanical and Process Engineering, ETH Zurich
, Zurich 8092, Switzerland
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a)
A. Spyrogianni and K. S. Karadima contributed equally to this work.
b)
Authors to whom correspondence should be addressed: vlasis@chemeng.upatras.gr and sotiris.pratsinis@ptl.mavt.ethz.ch
J. Chem. Phys. 148, 064703 (2018)
Article history
Received:
November 04 2017
Accepted:
January 14 2018
Citation
Anastasia Spyrogianni, Katerina S. Karadima, Eirini Goudeli, Vlasis G. Mavrantzas, Sotiris E. Pratsinis; Mobility and settling rate of agglomerates of polydisperse nanoparticles. J. Chem. Phys. 14 February 2018; 148 (6): 064703. https://doi.org/10.1063/1.5012037
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