Effects of the Charge-Dipole Interaction on the Coagulation of Fractal Aggregates

IEEE Trans. Plasma Sci.

Hayes

Freed

et al. 2007

Abstract-Planetary formation is an efficient process now thought to take place on a relatively short astronomical time scale. Recent observations have shown that the dust surrounding a protostar emits more efficiently at longer wavelengths as the protoplanetary disk evolves, suggesting that the dust particles are coagulating into fluffy aggregates, "much as dust bunnies form under a bed."One poorly understood problem in this coagulation process is the manner in which micron-sized, charged grains form the fractal aggregate structures now thought to be the precursors of protoplanetary disk evolution. This study examines the characteristics of such fractal aggregates formed by the collision of spherical monomers and aggregates where the charge is distributed over the aggregate structure. The aggregates are free to rotate due to collisions and dipole-dipole electrostatic interactions. Comparisons are made for different precursor size distributions and like-charged, oppositelycharged, and neutral grains.

Section: Introductionmentioning

confidence: 61%

Formation of Cosmic Dust Bunnies

IEEE Trans. Plasma Sci.

Hayes

Freed

et al. 2007

“…The computer model employed has previously been used to examine the coagulation of charged particles, as well as coagulation considering the influence of magnetic materials Matthews & Hyde (2004, Perry et al (2010). The current model incorporates an extended parameter space including velocity, radius, impact parameter, rotations, charge, density, magnetization and dipole interactions, among others.…”

Section: Methodsmentioning

confidence: 99%

“…Several numerical models investigating the dynamics and properties of dust aggregates have recently been published Dominik & Nubold (2002), Ormel et al (2006), Matthews & Hyde (2004, Perry et al (2010). In these models, individual dust particles collide to create aggregate structures which are fractal or fluffy in nature Blum et al (2000); Dominik et al (2007a).…”

Section: Introductionmentioning

confidence: 99%

The influence of monomer shape on aggregate morphologies

Perry

Gostomski

et al. 2012

A&A

Context. The coagulation of dust particles is the initial step in planetary formation, with the precursors to planetesimals believed to form via the collisions of micron and submicron sized dust particles in the disk surrounding a newly formed protostar. One of the usual assumptions in numerical models of aggregation is that of spherical monomers. However, the polarization of light in the interstellar medium (ISM) indicates that dust particles may not necessarily be spherical. Aims. This study investigates the influence of monomer shape (ellipsoidal vs. spherical) on the morphology of aggregates. The ellipsoidal grains used are prolate with an axis ratio of 3:1:1, which current evidence suggests as a possible shape for instellar dust grains. Methods. Populations of aggregates are built from ellipsoidal monomers and spherical monomers using both particle-cluster aggregation (PCA) and cluster-cluster aggregation (CCA) regimes incorporating the rotation of particles. The morphology of the resulting aggregates is compared using the maximum radius, porosity, fractal dimension, compactness factor and friction time. The last two factors indicate how the dynamics of a population of dust may be altered depending on monomer shape. Results. The results of this study indicate that monomer shape plays an important role in determining the final morphology of aggregates. Comparing ellipsoid grains with 3:1:1 axis ratio to spheres, the greatest difference is seen in compactness factors: (∼18%) for the PCA regime, reaching a maximum of (∼80%) for the CCA regime. The influence on porosity is also appreciable, (∼8%) and (∼15%) for PCA and CCA regimes respectively. The resulting differences for the friction times depend on the collision regime employed, yet show a marked difference for the different monomer shapes, (∼12%) for PCA and (>50%) for CCA at large sizes. It is concluded that the effect of monomer shape in the hit-and-stick aggregation model may produce appreciable structural variation in the final aggregate. Present models of fluffy aggregates made up of only spherical monomers therefore may not be the best representation for grains in some astrophysical environments.

“…For monodisperse particles, as used in this study, Q 0 = Nq 0 , with q 0 the (fixed) charge on a given monomer and p 0 is the magnitude of the electric dipole moment calculated for a total charge Q 0 with the charge arranged such that monomers furthest from the COM have the greatest fraction of the charge [6]. It should be noted that the magnitude of the dipole moment is not wellcorrelated with N, nor is it well-correlated with the fractal dimension, F d .…”

Section: Methodsmentioning

confidence: 99%

“…The ambient dust environment can have a significant effect on grain coagulation: grains immersed in plasma can become charged, which can either retard or enhance coagulation rates depending on charging conditions [6,7]. If dust grains in a population charge to a potential of the same sign, the coagulation rate can be reduced or even halt altogether due to the resulting electrostatic repulsion depending on the relative speeds between the grains.…”

Section: Introductionmentioning

confidence: 99%

Dipole–Dipole Interactions of Charged-Magnetic Grains

Perry

IEEE Trans. Plasma Sci.

Hyde

2010

Abstract-The interaction between dust grains is an important process in fields as diverse as planetesimal formation or the plasma processing of silicon wafers into computer chips. This interaction depends in large part on the material properties of the grains, for example whether the grains are conducting, nonconducting, ferrous or non-ferrous. This work considers the effects that electrostatic and magnetic forces, alone or in combination, can have on the coagulation of dust in various environments. A numerical model is used to simulate the coagulation of charged, charged-magnetic and magnetic dust aggregates formed from ferrous material and the results are compared to each other as well as to those from uncharged, nonmagnetic material. The interactions between extended dust aggregates are also examined, specifically looking at how the arrangement of charge over the aggregate surface or the inclusion of magnetic material produces dipole-dipole interactions. It will be shown that these dipole-dipole interactions can affect the orientation and structural formation of aggregates as they collide and stick. Analysis of the resulting dust populations will also demonstrate the impact that grain composition and/or charge can have on the structure of the aggregate as characterized by the resulting fractal dimension.