Luminescence from Collapsing Centimeter Bubbles Expanded by Chemical Reaction

We report on a new method for realizing an exceptionally strong inertial confinement of a gas in a liquid: A centimetric spherical bubble filled with a reactive gaseous mixture in a liquid is expanded by an exothermic chemical reaction whose products condense in the liquid at the bubble wall. Hence, the cavity formed in this way is essentially empty as it collapses. The temperatures reached at maximum compression, inferred from the cavity radius dynamics and further confirmed by spectroscopic measurements exceed 20 000 K. Because the cavity is typically big, our findings also provide unique space and time resolved sequences of the events accompanying the collapse, notably the development of the inertial instability notoriously known to deter strong compression.

Figure 1

Expansion and collapse dynamics of a stoichiometric hydrogen-oxygen mixture ignited in a bubble immersed in a liquid. (a) In glycerol, from ignition to maximal compression, by time steps of 0.7 ms. The width of the images is 3.3 cm. Closeup of the collapsed bubble 0.1 ms after maximal compression (image width 1 cm), showing interface destabilization. (b) In water, time steps of 0.45 ms from ignition, images width is 2 cm, showing a light flash at maximal compression, rebound, and fragmentation of the bubble. (c) Detailed dynamics around maximal compression, showing light emission, and interface destabilization. Glycerol, time step of $6.6\mu \mathrm{s}$, image width 9.8 mm. (See the movies in the Supplemental Material for time resolved sequences.)

Figure 2

Radius trajectories $R(t)$ for bubbles with several different radii $R_0$ in water (insert), and trajectories rescaled by their maximum $R_{\max }$, and time by $\tau =R_{\max }\sqrt{\rho /P_{\text{atm}}}$. Comparison with the solution of Eq. (2), with $P=0$ (grey line) and $P=P_0[R(t)/R_0{]}^{-3\gamma }$, with $P_0/P_{\text{atm}}=0.6$ (dashed line).

Figure 3

Blue dots: Bubble radius close to its minimum [corresponding to Fig. 1], at the maximum compression time $t_{\star }$, as the trajectory rebounds. Dashed line: Parabolas $R(t)=R(t_{\star })+\ddot{R}(t_{\star })[t-t_{\star }{]}^2/2$. Red dots: Luminance of the flash (a.u.). $\tau =1.5\mathrm{ms}$.

Figure 4

Spectral content (wavelength in nanometers) of the light emitted during the combustion stage (black), and during the flash (red) maximal bubble compression, integrated for a time ${\tau }_e=50\mu \mathrm{s}$. Inserts: Raw snapshots of the flame (top) and of the flash (bottom) as recorded behind a grating.