Chemical oscillations of air-seeded bubbles in water driven by ultrasound

Chemical oscillations are shown to be responsible for very low frequency modulations of a bubble oscillating nonlinearly in a high intensity ultrasound field. In the parameter space of incomplete dissociation near the onset of sonoluminescence a small bubble is shown to grow on a long time scale by the intake of dissolved air. Bubble collapses get hotter and more dense, noninert gases are dissociated and removed, and a small growing argon bubble is left behind continuing the circle.

Figure 1

Histogram of collapse times. From data of Fig. 2a.

Figure 2

Quasiperiodic modulation on long time scales of an oscillating bubble. From top to bottom as a function of time is shown: (a) collapse time, (b) maximal radius (straight line) and equilibrium radius (dashed), and (c) levitation position (height-difference from the center of the resonator cell).

Figure 3

Radius-time curves of bubble at minimum and maximum of the oscillation shown in Fig. 2. The small bubble contains 94% argon; the big bubble contains 79% nitrogen.

Figure 4

Quasiperiodic modulation on long time scales of an oscillating bubble. From top to bottom as a function of time is shown: (a) molecules of ${\mathrm{H}}_2\mathrm{O}$ (straight) and ${\mathrm{O}}_2$ (dotted); (b) molecules of ${\mathrm{N}}_2$ (straight) and Ar (dashed); (c) dissociation (straight) and diffusion rate (dashed) of ${\mathrm{N}}_2$ and ${\mathrm{O}}_2$ (dotted); (d) diffusion rate of Ar; and (e) temperature (straight) and density (dashed) in the bubble at collapse.

Figure 5

Slow quasiperiodic oscillations of the maximum radius as a function of time for decreasing driving amplitude (from top to bottom: $119800\mathrm{Pa}$, $119600\mathrm{Pa}$, $119500\mathrm{Pa}$, $119400\mathrm{Pa}$, and $119200\mathrm{Pa}$ (dotted)]. The driving frequency is $14.620\mathrm{kHz}$, and the ambient pressure is $103351\mathrm{Pa}$ augmented by the hydrostatic pressure at water depth $4.36\mathrm{cm}$.