Catastrophic Collapse of Particulate Clouds: Implications From Aggregation Experiments in the USML-1 and USML-2 Glovebox

Experiments with electrostatic aggregation of well-dispersed (nominally, mono-dispersed), freely suspended particles in the United States Microgravity Laboratory (USML) Glovebox have determined that filamentary aggregates are a universal product of grain interactions in relatively dense particulate clouds. Aggregate growth from the experimental particle clouds primarily involves dipole-dipole interactions for nonconducting materials; dipole interactions account for both attraction between grains as well as the cohesive force that maintains the integrity of the filamentary structures. When a cloud undergoes a turbulent-to-quiescent transition after damping of fluid and ballistic grain motions, aggregation occurs almost instantaneously and the cloud is transformed into a population of "heavier" clusters of material with organized electrical structures. This abrupt transformation could initiate catastrophic gravitational collapse of certain regions of particulate clouds, thus controlling the longevity and fate of cloud systems as diverse as protoplanetary dust disks and volcanic eruption plumes.