The
motion of particles in a monolayer induced by the coalescing
of a bare bubble with a planar air–water interface was investigated
in a modified Langmuir trough. Experiments were performed to understand
the effect of particle hydrophobicity, subphase pH, packing density,
the presence of a weak surfactant, and particle size distribution
on the behavior of particle movement in the monolayer during the coalescence
process. Video tracking software was used to track the particles and
extract data based on the video footage. Visual inspection indicated
that the coalescence of the bubble with the monolayer was a chaotic
process which led the interface to oscillate to an extent that the
particles underwent complete rearrangement. A simple analysis was
carried out on the main forces involved in particle motion and rearrangement
at the oscillating air–water interface. The motion characteristic
of particles was evaluated by speed and mean-square displacement (MSD).
The results showed that the butanol-treated particles had higher speed
and MSD than the particles with a stronger affinity to the air–water
interface. Similar results were also found at high subphase pH and
low packing factor.