  Context. Particles in protoplanetary disks go through a number of phases that
are dominated by collisions. In each of these events, grains exchange
electrical charge via triboelectric effects. This enhances the stability of
particle aggregates. Aim. Dielectric grains are easily charged by collisions.
Here, we investigate whether a charge is capable of inducing an aggregation of
particles and we consider how collision properties, such as ticking velocities
and collisional cross-sections, are altered. Methods. We explored aggregation
in microgravity experiments based on the observation of the motion of
submillimeter (submm) grains following many collisions. In the process, grains
attract each other, collide, stick, and ultimately form small aggregates.
Results. We observed a bottom-up formation of irregular aggregates from submm
grains. While some of the observed trajectories during the approach of grains
reflect the presence of a pure Coulomb potential, the motion is not always in
agreement with pure Kepler motion. Higher-order potentials of multipole charge
distributions stand as a plausible explanation for this behavior. An immediate
consequence of charging is that the particles continue to stick to each other
at velocities of $\sim 10 \, \rm cm/s,$ while surface forces of neutral grains
are only expected to allow sticking below $\sim 1 \, \rm mm/s$. No bouncing
collision was observed among hundreds of collisions in the given parameter
range. Applied to early phases of planet formation, the forming aggregates are
therefore the first steps in a new growth phase beyond the traditional bouncing
barrier in planet formation.
