An experimental apparatus was developed based on the Langmuir-Blodgett trough design to investigate the compression of monolayers of micron size spherical glass particles at the air-water interface and the interaction of an air bubble with the monolayers. The setup modifies the regular Langmuir-Blodgett trough by using a deep and clear glass cell. The cell allowed both the optical observation of the particle monolayer and the insertion of a capillary to produce a bubble under the layer of particles. Surface pressure-area (Π-A) isotherms were measured while the particles rearranged at the interface during compression and expansion for different pH values and particle wettability. We also analyzed the motion of particles in the monolayer by the surface pressure and packing factor to gain further insights into the behavior of particles during the coalescence process. The results suggested that the coalescence of a bubble was dependent on the formation of a defect in the particle layer and the defect size was both strongly influenced by particle hydrophobicity and the pH of the subphase.
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.
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