Contact Forces between Single Metal Oxide Nanoparticles in Gas-Phase Applications and Processes

Salameh, Samir; Veen, Monique A. van der; Kappl, Michael; Ommen, J. Ruud van

doi:10.1021/acs.langmuir.6b02982

Cited by 19 publications

(15 citation statements)

References 59 publications

(141 reference statements)

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“…If agglomerates had collapsed during water condensation, the critical S should decrease with the increasing surface hydrophilicity as the capillary forces between PPs and aggregates increase. 42 However, our data and those of Ma et al 28 indicate that this is not the case. Bambha et al 36 showed that restructuring depends on the method used to dry soot agglomerates and, thus, on the evaporation rate of condensed oleic acid.…”

Section: Methodscontrasting

confidence: 73%

“…The surface of metal oxides is more hydrophilic than that of the soot because of their hydroxyl groups that facilitate water adsorption . The attractive capillary force between rather hydrophilic metal oxides, such as titania, , alumina, and silica, was measured and/or estimated in the range of 2–8 nN during water condensation for S < 1. Furthermore, colliding soot particles form aggregates by reactions with acetylene or polycyclic aromatic hydrocarbon molecules with collision diameter less than 1 nm .…”

Section: Introductionmentioning

confidence: 99%

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Impact of Humidity on Silica Nanoparticle Agglomerate Morphology and Size Distribution

et al. 2018

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The effect of humidity on flame-made metal oxide agglomerate morphology and size distribution is investigated, for the first time to our knowledge, and compared to that on soot, which has been widely studied. Understanding the impact of humidity on such characteristics is essential for storage, handling, processing, and eventual performance of nanomaterials. More specifically, broadly used agglomerates of flame-made silica nanoparticles are humidified at various saturation ratios, S = 0.2-1.5, and dried before characterization with a differential mobility analyzer (DMA), an aerosol particle mass (APM) analyzer, and transmission electron microscopy. At high humidity, the constituent single and/or aggregated (chemically bonded) primary particles (PPs) rearrange to balance the capillary forces induced by condensation-evaporation of liquid bridges between PPs. Larger agglomerates restructure more than smaller ones, narrowing their mobility size distribution. After humidification at S = 1.5 and drying, agglomerates collapse into compact structures that follow a fractal scaling law with mass-mobility exponent D = 3.02 ± 0.11 and prefactor k = 0.27 ± 0.07. This critical S = 1.5 for silica agglomerates is larger than the 1.26 obtained for soot because of the hydrophilic surface of silica that delays water evaporation. The relative effective density, ρ/ρ, of collapsed agglomerates becomes invariant of mobility diameter, d, similar to that of fluidized and spray-dried granules. The average silica ρ/ρ = 0.28 ± 0.02 is smaller than the 0.36 ± 0.04 measured for the humidified-dried soot because of the larger size of silica aggregates, d/ d, and number of constituent primary particles, n, of diameter d. This is verified by tandem-DMA (TDMA) measurements, yielding maximum d = 3 d or 5 d and n = 13 or 36 for the soot or silica aggregates studied here, in good agreement with those reported from microscopy and high-pressure agglomerate dispersion. A scaling law relating the initial d to d, D, and k after condensation-drying is developed. The mass-mobility relationship of collapsed silica and soot agglomerates obtained by combining this law with fast TDMA measurements is in excellent agreement with that measured by the direct, but tedious, DMA-APM analysis.

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Section: Methodscontrasting

confidence: 73%

Section: Introductionmentioning

confidence: 99%

Impact of Humidity on Silica Nanoparticle Agglomerate Morphology and Size Distribution

et al. 2018

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“…where σ mon is the standard deviation of possible monomer sizes (Slobodrian et al 2011;Bescond et al 2014;Kandilian et al 2015;Wu et al 2020;Zhang et al 2020). In order to construct our dust aggregates we take typical laboratory values of σ mon = 1.25 nm, a mean = 16 nm, and for the scaling factor we choose k f = 1.3 (Salameh et al 2017;Wang et al 2019;Wu et al 2020;Zhang et al 2020;Kim et al 2021). All monomer sizes are sampled from Eq.…”

Section: Dust Grain Modelmentioning

confidence: 99%

“…Kozasa et al 1992;Shen et al 2008). However, laboratory data suggests that a plethora of different materials form fractal aggregates composed of monomers with variable sizes (Chakrabarty et al 2007;Slobodrian et al 2011;Kandilian et al 2015;Baric et al 2018;Kelesidis et al 2018;Salameh et al 2017;Wu et al 2020;Zhang et al 2020;Kim et al 2021). The size distribution of the monomers itself may follow a log-normal distribution…”

Section: Dust Grain Modelmentioning

confidence: 99%

The Mechanical Alignment of Dust (MAD) I: On the spin-up process of fractal grains by a gas-dust drift

Reißl¹,

Meehan²,

Klessen³

2022

Preprint

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Context. Observations of polarized light emerging from aligned dust grains are commonly exploited to probe the magnetic field orientation in astrophysical environments. However, the exact physical processes that result in a coherent large-scale grain alignment are still far from being fully constrained. Aims. In this work, we aim to investigate the impact of a gas-dust drift on a microscopic level potentially leading to a mechanical alignment of fractal dust grains and subsequently to dust polarization. Methods. We scan a wide range of parameters of fractal dust aggregates in order to statistically analyze the average grain alignment behavior of distinct grain ensembles. In detail, the spin-up efficiencies for individual aggregates are determined utilizing a Monte-Carlo approach to simulate the collision, scattering, sticking, and evaporation processes of gas on the grain surface. Furthermore, the rotational disruption of dust grains is taken into account to estimate the upper limit of possible grain rotation. The spin-up efficiencies are analyzed within a mathematical framework of grain alignment dynamic in order to identify long-term stable grain alignment points in the parameter space. Here, we distinguish between the cases of grain alignment in direction of the gas-dust drift and the alignment along the magnetic field lines. Finally, the net dust polarization is calculated for each collection of stable alignment points per grain ensemble.Results. We find the purely mechanical spin-up processes within the cold neutral medium to be sufficient enough to drive elongated grains to a stable alignment. The most likely mechanical grain alignment configuration is with a rotation axis parallel to the drift direction. Here, roundish grains require a supersonic drift velocity while rod-like elongated grains can already align for subsonic conditions. We predict a possible dust polarization efficiency in the order of unity resulting from mechanical alignment. Furthermore, a supersonic drift may result in a rapid grain rotation where dust grains may become rotationally disrupted by centrifugal forces. Hence, the net contribution of such a grain ensemble to polarization becomes drastically reduces. In the presence of a magnetic field the drift velocity required for grains to reach a stable alignment is roughly one order of magnitude higher compared to the purely mechanical case. We demonstrate that a considerable fraction of a grain ensemble can stably align with the magnetic field lines. We report a possibly dust polarization efficiency of 0.8 − 0.9 indicating that a gas-dust drift alone can provide the conditions required to observationally probe the magnetic field structure. We predict that the magnetic field alignment is highly inefficient when the direction of the gas-dust drift and the magnetic field lines are perpendicular. Conclusions. Our results strongly suggest that mechanical alignment has to be taken into consideration as an alternative driving mechanism where the standard RAT alignment theory fails to account f...

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“…In the trajectory with three particles, two particles are always in contact with each other, while the third particle moves freely around the other two; in the trajectories with four particles, particles are always in contact with their neighbors. A bond is formed between the two sticking particles by short-range cohesive forces, including van der Waals forces or capillary forces due to absorbed molecular layers 12,41,42 . These short range interactions are strong enough to hold the two particles together without relative translational and rotational momentum between each other.…”

Section: Application To Experimental Trajectoriesmentioning

confidence: 99%

Evolutionary strategy for inverse charge measurements of dielectric particles

Jiang

Lee

et al. 2018

The Journal of Chemical Physics

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We report a computational strategy to obtain the charges of individual dielectric particles from experimental observation of their interactions as a function of time. This strategy uses evolutionary optimization to minimize the difference between trajectories extracted from the experiment and simulated trajectories based on many-particle force fields. The force fields include both Coulombic interactions and dielectric polarization effects that arise due to particle-particle charge mismatch and particle-environment dielectric contrast. The strategy was applied to systems of free falling charged granular particles in a vacuum, where electrostatic interactions are the only driving forces that influence the particles' motion. We show that when the particles' initial positions and velocities are known, the optimizer requires only an initial and final particle configuration of a short trajectory in order to accurately infer the particles' charges; when the initial velocities are unknown and only the initial positions are given, the optimizer can learn from multiple frames along the trajectory to determine the particles' initial velocities and charges. While the results presented here offer a proof-of-concept demonstration of the proposed ideas, the proposed strategy could be extended to more complex systems of electrostatically charged granular matter.

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Contact Forces between Single Metal Oxide Nanoparticles in Gas-Phase Applications and Processes

Cited by 19 publications

References 59 publications

Impact of Humidity on Silica Nanoparticle Agglomerate Morphology and Size Distribution

Impact of Humidity on Silica Nanoparticle Agglomerate Morphology and Size Distribution

The Mechanical Alignment of Dust (MAD) I: On the spin-up process of fractal grains by a gas-dust drift

Evolutionary strategy for inverse charge measurements of dielectric particles

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