Experimental Technique to Study the Interaction Between a Bubble and the Particle-Laden Interface

Abstract

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.

Motion of Particles in a Monolayer Induced by Coalescing of a Bubble with a Planar Air–Water Interface

“…It was assumed that the treatment of the particles did not affect the charge of the particles. As argued by Bournival 26 (see also Yang et al 20 ), the esterification treatment of the particles does not affect the zeta potential of the particles. That is, the low surface coverage of the alkyne coating, which was estimated to 1.57 groups per nm 2 for octane 27 does not reduce the initial number of silanol groups 28 sufficiently to affect the charge of the particles.…”

“…The surface of the particles was esterified using 1-octanol (Sigma-Aldrich, 99%) and 1-butanol (Chem-Supply, 99%). More information on the preparation of the particles can be found in Yang et al 20 The hydrophobicity of the particles was determined from contact angle measurements on esterified glass plates. The contact angle was measured by submerging the plate in the modified Langmuir trough, which was filled with water topped with a layer of toluene, reproducing the experimental conditions for the production of a particle monolayer.…”

“…Experiments were conducted in a temperature-controlled laboratory at 22 ± 1.5 °C. More details on the setup and methodology are in Yang et al 20 All particles tracked were at a radial distance of 2 mm away from the apex of the bubble. In some instances (Section 3.5), measurements were taken at 1.5, 2, and 2.5 mm from the bubble.…”

“…In some instances (Section 3.5), measurements were taken at 1.5, 2, and 2.5 mm from the bubble. The packing factor was measured using image processing following the method described in Yang et al 20 This packing factor is a local packing factor around the bubble and was measured offline from the recorded videos. As such, the packing factor was subject to variations.…”

“…The experimental setup allowed the structure of a particle monolayer formed at an air−water interface to be manipulated and the packing density to be adjusted in a controllable way. 20 After coalescence, a wave spread from the contact point and propagated outward, leading to the periodic local surface compression and expansion. In response, the particles trapped at the interface rose and fell and underwent rearrangement at the same time.…”