119 research outputs found
Direct Observation of the Dynamics of Latex Particles Confined inside Thinning Water-Air Films
The dynamics of micrometer-size polystyrene latex particles confined in thinning foam films was
investigated by microscopic interferometric observation. The behavior of the entrapped particles depends
on the mobility of the film surfaces, the particle concentration, hydrophobicity, and rate of film formation.
When the films were stabilized by sodium dodecyl sulfate, no entrapment of particles between the surfaces
was possible. When protein was used as a stabilizer, a limited number of particles were caught inside
the film area due to the decreased mobility of the interfaces. In this case, extraordinary long-ranged (>100
Ìm) capillary attraction leads to two-dimensional (2D) particle aggregation. A major change occurs when
the microspheres are partially hydrophobized by the presence of cationic surfactant. After the foam films
are opened and closed a few times, a layer of particles simultaneously adsorbed to the two interfaces is
formed, which sterically inhibits any further film opening and thinning. The particles within this layer
show an excellent 2D hexagonal ordering. The experimental data are relevant to the dynamics of defects
in coating films, Pickering emulsions, and particle assembly into 2D arrays
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