S054022 Effect of Pressure-Oscillation on Flow Birefringence between and around Vertically Aligned Bubbles

Abstract

When strong pressure-oscillation was applied to the two vertically aligned air bubbles in viscoelastic fluids from the bottom side, the lower-bubble rose faster than the upper-bubble. It is thought that a hydrodynamic interaction may be occurred in the fluid between air bubbles. To clarify the stress contribution on the interaction, we tried measuring the retardation profile near and between the vertically aligned small air bubbles under pressure-oscillating fields, by using the flow birefringence technique with CTAB / NaSal solution. In the case of near the bubbles (2μL for each), it was found that the stronger retardations were observed as approaches to the bubble surface under pressure-oscillating field, as well as the higher frequency. The higher uniaxial strain rate (about the order of 10) was obtained in vicinity of small air bubbles. However, in the case at the bubbles center, the moderate elongational velocity was observed. As for the between the two bubbles, the relatively flat retardation profile was also obtained.