Computer simulations of cluster–cluster aggregation

R, Jullien; Botet, Robert; Mors, Paulo Machado

doi:10.1039/dc9878300125

Cited by 78 publications

(59 citation statements)

References 1 publication

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“…For any N there exists a distribution of aggregate morphologies defined by the orientation of a monomer or collection of monomers with respect to its neighbors. Using clustercluster aggregation theory, studies have successfully modeled both soot aggregate formation and growth into a lacey structure with a D f consistent with measured values (20,24,25). From these investigations, a picture emerges of soot aggregates that have ramified structure similar to the macroscale aggregates used in this study.…”

Section: Significancementioning

confidence: 79%

“…Model aggregates were generated using the cluster-cluster aggregation. D f was varied from 1.55 to 2.25, a value of 1.6 of k N was used for all aggregates (24,25,34). Aggregates from N = 3-12 were studied.…”

Section: Methodsmentioning

confidence: 99%

“…The R g scales linearly with N for aggregates with 3 ≤ N ≤ 12 ( Fig. S4) (20,24,25,34). Across the series from individual aggregates to those observed in comet nuclei, the value of N ranged from three per aggregate to 6 × 10 7 per aggregate, and a spanned from 17 nm for soot to 6 mm for macroscale monomers (30).…”

Section: Significancementioning

confidence: 99%

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Packing density of rigid aggregates is independent of scale

Zangmeister

Radney

Dockery

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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Large planetary seedlings, comets, microscale pharmaceuticals, and nanoscale soot particles are made from rigid, aggregated subunits that are compacted under low compression into larger structures spanning over 10 orders of magnitude in dimensional space. Here, we demonstrate that the packing density (θ f ) of compacted rigid aggregates is independent of spatial scale for systems under weak compaction. The θ f of rigid aggregated structures across six orders of magnitude were measured using nanoscale spherical soot aerosol composed of aggregates with ∼17-nm monomeric subunits and aggregates made from uniform monomeric 6-mm spherical subunits at the macroscale. We find θ f = 0.36 ± 0.02 at both dimensions. These values are remarkably similar to θ f observed for comet nuclei and measured values of other rigid aggregated systems across a wide variety of spatial and formative conditions. We present a packing model that incorporates the aggregate morphology and show that θ f is independent of both monomer and aggregate size. These observations suggest that the θ f of rigid aggregates subject to weak compaction forces is independent of spatial dimension across varied formative conditions. M any systems are comprised of elementary subunits packed within a defined volume. The simplest 3D system consists of uniform spheres, and despite its apparent simplicity, a rigorous mathematical description eluded researchers for nearly four centuries dating back to Kepler's conjecture in 1611. In 2005, Hales provided a definitive mathematical proof confirming the observed experimental maximum packing density of 74% (1). Packing of more complex structures is far more mathematically challenging and instead relies on empirical studies (2-9). One of the most ubiquitous packing systems in the universe are rigid aggregates composed of a collection of monomeric units joined together into a fractal structure and subsequently densified through omnidirectional applied force, as shown in Fig. 1 (10).The formation and compaction mechanism of disordered aggregates is presumed to be independent of dimension, composition, and spatial scale, and has been observed in a diverse range of materials and conditions, such as the accretion of material in interstellar space and the formation and compaction of aerosol in the Earth's atmosphere. Many interstellar formations comprise nano-or microscale dust particles that begin as disordered monomeric subunits, which electrostatically aggregate to form fractal (lacey) agglomerates that serve as foundries for comets and planetary seedlings (10-16). Soot, ubiquitous in the Earth's troposphere, is also comprised of nanometer sized carbonaceous monomers aggregated in a disordered lacey structure. Compaction into spheres occurs after trace gas and/or liquid adsorption and evaporation. In both cases, the resulting structure is constrained by aggregate rigidity (17).The systems described above are similarly constructed from single-unit building blocks assembled into larger disordered structures. The final structure ...

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Section: Significancementioning

confidence: 79%

Section: Methodsmentioning

confidence: 99%

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Packing density of rigid aggregates is independent of scale

Zangmeister

Radney

Dockery

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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“…[10][11][12][13][14][15] Depending on the sticking probability (p s ) between two colloidal particles, the process can be characterized as the diffusion-limited cluster-cluster aggregation (DLCA, p s ∼ 100%) and the reaction-limited cluster-cluster aggregation (RLCA, p s , 100%). 16,17 One distinctive feature between DLCA and RLCA is their different scalings between the mass (M) and size (R) of the aggregates, that is, different…”

Section: Introductionmentioning

confidence: 99%

Observation of Kinetic and Structural Scalings during Slow Coalescence of Nanobubbles in an Aqueous Solution

Jin

2007

J. Phys. Chem. B

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The addition of salt can induce the slow coalescence of nanobubbles (∼100 nm) in an aqueous solution of R-cyclodextrin (R-CD). A combination of static and dynamic laser light scattering was used to follow the coalescence. Our results reveal that its kinetic and structural properties follow some scaling laws; namely, the average size (< >) of the nanobubbles is related to their average mass () and the coalescence time (t) as ∼ < > d f and < > ∼ t γ with two salt-concentration-dependent scaling exponents (d f and γ). For a lower sodium chloride concentration (C NaCl ) 40 mM), γ ) 0.13 ( 0.01 and d f ) 1.71 ( 0.02. The increase of C NaCl to 80 mM results in γ ) 0.32 ( 0.01 and d f ) 1.99 ( 0.01. The whole process has two main stages: the aggregation and the coalescence. At the lower C NaCl , the process essentially stops in the aggregation stage with some limited coalescence. At higher C NaCl , coalescence occurs after the aggregation and results in large bubbles.

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“…On the basis of observations of many BCA particles collected over the past several years, we find that the morphology of stratospheric and upper tropospheric BCA is very similar to that observed for other types of BCA originating from combustion processes, from diesel exhaust soot to biomass burning, all of which can be described as fractal aggregates. The formation of aerosol aggregates has been described in terms of clustercluster models [Jullien, 1987]. Previous studies on BCA formation have determined that a diffusion limited clustercluster mechanism dominates.…”

mentioning

confidence: 99%

Carbonaceous aerosol (soot) measured in the lower stratosphere during POLARIS and its role in stratospheric photochemistry

Strawa¹,

Drdla²,

Ferry³

et al. 1999

J. Geophys. Res.

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in the laboratory, Thlibi and Petit [1994] found that the reduction of HNO3 to NO occurred on carbon. Rogaski et al. [1997] found that the major products of the heterogeneous reaction of HNO3 with BCA were H20, NO2, and NO and reported an uptake coefficient of 3.8 x 10 •. They measured two NOx molecules produced for every three HNO3 molecules adsorbed. More recently, however, Choi and Leu [1998] on carbon between 10 -3 and 10 -5 depending on carbon sample surface history, with CO, CO2, and 02 as products. The presence of these products suggests that the ozone reaction on carbon is, at lest in part, noncatalytic.This paper discusses the measurement of BCA by the Ames Wire Impactors and assesses the role of BCA in stratospheric photochemistry. A new method of analyzing impactor samples is described that accounts for particle bounce and models the BCA as fractal aggregates to modify the aerodynamic collection efficiency and determine particle surface area. Results from the present analysis are compared with previous techniques and with BCA surface area values used in previous model simulations. The photochemical trajectory model used in the present simulations is described. An assessment of the importance of heterogeneous BCA reactions is made by comparing modeled and measured NOJNOy ratios and effects on ozone loss. Finally, the implications of mass-balancing these reactions on the lifetime of BCA particles in the stratosphere will be discussed. The Ames Wire ImpactorThe Ames Wire Impactor (AWI) has been used extensively in the past on such missions as AAOE, AASE, AASE II, ASHOE/MAESA, and POLARIS to sample stratospheric aerosol. It has proven to be an accurate and reliable means for obtaining atmospheric aerosol size distributions, and sulfate and BCA burdens. The sampler consists of palladium and/or gold wires of 75-and 500-p,m diameter that are strung across support rings. The wires are carbon coated and modules are assembled in a class 100 clean room. Up to six modules are mounted on the wingtip of the ER-2. Each module has the capability of holding several rings with several wires on each ring. The modules are exposed to the free stream by preselected triggers of time, altitude, or aircraft position. Aerosol particles suspended in the ambient air impact on the wires. A new automated sample actuation system was designed, fabricated, and successfully used to retrieve data during the POLARIS campaign. Samples were exposed typically for 3 min. Particles stick to the wire upon impact by virtue of van der Waals forces. After exposure, the wires are retracted into sealed modules containing concentrated ammonia vapor. The ammonia combines with the sulfuric acid aerosol to form ammonium sulfate which is very stable under laboratory conditions and allows for the sample to be stored indefinitely. Particles are manually identified, counted, and sized using a Hitachi S-4000 field emission scanning electron microscope. Under the conditions used for imaging, the lateral resolution of the microscope is better than 10 nm....

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Computer simulations of cluster–cluster aggregation

Cited by 78 publications

References 1 publication

Packing density of rigid aggregates is independent of scale

Packing density of rigid aggregates is independent of scale

Observation of Kinetic and Structural Scalings during Slow Coalescence of Nanobubbles in an Aqueous Solution

Carbonaceous aerosol (soot) measured in the lower stratosphere during POLARIS and its role in stratospheric photochemistry

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