Dynamics of oil encapsulated bubbles

The dynamics of oil encapsulated bubbles was experimentally investigated. High-speed imaging was employed in the visualization of the motion of oil coated bubbles rising in quiescent tap water. The attachment of isolated bubbles with diameters ranging from 300 to 3000 μm to a 2.3 mm oil droplet resulted in two different regimes: oscillatory and non-oscillatory motion. The influence of the oil coating was investigated by employing three different oils, whose properties have shown to be more influential when no motion instabilities were observed. Path oscillations were found to decrease for encapsulated bubbles, being up to five times smaller in comparison with isolated bubbles with similar diameter. Oil coated bubbles presented higher terminal velocities in comparison to droplets of corresponding diameter, with increase factors from 100 up to 400%. The maximum shape deformation (13%) was observed for larger bubbles, approximately 8 times smaller than for isolated bubbles. Transient motion assays indicated that developed regime was achieved in approximately half the rising distance than for isolated bubbles, after which a periodic oscillation of the velocity components was observed.