Multibubble Sonoluminescence Research Articles

Multibubble sonoluminescence of europium(III) chloride in heavy water

A weak glow in the region of the Eu3+ photoluminescence spectrum was detected against the background of the continuum of the solvent emission during multibubble sonolysis of air- or argon-saturated EuCl3 solutions (0.1 mol L−1) in heavy water. No characteristic sonoluminescence of the europium ion in aqueous solutions was observed earlier. Possible reasons for the low yield of Eu3+ sonoluminescence compared with other lanthanide ions (Ln3+) are discussed and the influence of europium on the spectrum of the solvent continuum related, in particular, to quenching of the electron-excited sonolysis products H2O* (D2O*) and Eu3+* in electron transfer reactions.

Sonoluminescence quenching in aqueous solutions of aliphatic diols and glycerol

The multibubble sonoluminescence (MBSL) signals that were generated using 358 kHz ultrasound in aqueous solutions of ethylene glycol, 1,3-propanediol, 1,4-butanediol and glycerol, over a range of concentrations, have been studied. It was found that the intensity of the MBSL was either reduced or enhanced, relative to the signal in water, depending on the concentration of the solute. It was concluded that the reduction in the MBSL intensity was dependent on the strength of the intermolecular forces, in particular hydrogen bonding, between the solute molecules and water. The enhancement in the MBSL signal was ascribed to presence of the solute molecules at the bubble/solution interface that hinder the coalescence of the bubbles in the multibubble clouds produced at the antinodes in the system.

Enhancement of Sonoluminescence and Bubble Dynamics using Pulsed Ultrasound at 103 kHz

Enhancement of multibubble sonoluminescence was observed for pulsed ultrasound at 103 kHz. High-speed photography was also used to obtain the images of cavitation bubbles at a frame rate of 150,000 fps in continuous wave mode and pulsed wave mode. Most bubbles oscillated spherically and showed frequent coalescence in continuous wave mode at an applied voltage of 28 Vpp. The maximum bubble radius was measured to be 20–30 µm. Only in pulsed wave mode the following complex structure of bubble oscillation was captured. The radii of bubbles that survived during the pulse-off time were in the range from 5 to 10 µm, and these act as bubble nuclei for the successive pulse. These bubble nuclei grow to large bubbles, which oscillate non-spherically and emit many tiny bubbles. The daughter bubbles oscillate spherically and probably contribute to the enhancement of sonoluminescence. Subharmonic components and the increase in broadband noise obtained in the acoustic spectrum result from bubbles oscillating non-spherically and chaotically.

Parametric dependence of the line emissions in sonoluminescence

Based on a series of spectral measurements of sonoluminescence, this paper investigates parametric dependence of the line emissions in single bubble sonoluminescence (SBSL) and multi-bubble sonoluminescence (MBSL). The experiments show that the intensities of the OH radical line, the sodium line and the noble gas lines in SBSL are relevant to the driving pressure of the acoustic field and the concentration of the noble gases dissolved in host liquids. The intensity of line emissions in total spectrum increases with the decreasing driving pressure and the increasing concentration of noble gases. Parametric dependence of line emissions in MBSL consists with that in SBSL. Line emissions in sonoluminescence should correspond to lower temperature inside the bubbles. SBSL and MBSL share the same spectral structure, and the difference between them found by previous experiments should result from the different temperatures inside bubbles.

Influence of Surface-Active Solutes on the Coalescence, Clustering, and Fragmentation of Acoustic Bubbles Confined in a Microspace

High-speed imaging was used to capture the effect of surface-active solutes on the behavior of acoustic bubbles, generated in a microspace using low-frequency ultrasound (60 kHz). By confining cavitation within a microspace, the dynamic behavior of bubbles, such as bubble coalescence, clustering, and fragmentation, could be observed directly. It was observed that bubbles coalesced instantly in water; however, in the presence of surface-active solutes (n-propanol and sodium dodecyl sulfate, SDS) the coalescence was hindered. Low-density bubble clusters were observed in the presence of 1 mM SDS and 0.1 M n-propanol. When 0.1 M sodium chloride was added to 1 mM SDS solution, the extent of clustering and the density of the clusters enhanced significantly; a similar observation was made at a higher SDS concentration (10 mM). The importance of these results in understanding multibubble sonoluminescence data published previously has been addressed. The collective oscillation of a bubble cluster consisting of different sized bubbles and images of bubbles emitting a fountain of microbubbles have also been presented.

Homogeneous ZnS coating onto TiO2 nanoparticles by a simple one pot sonochemical method

Abstract TiO2 nanoparticles were easily coated with ZnS in nano-scale through a simple one pot reaction under multibubble sonoluminescence (MBSL) conditions which can provide a very powerful and efficient coating system. The coating depths of ZnS shell were in 2–5 nm range in a core/shell type nanostructure which is very likely to be useful for the development of inorganic dye-sensitized solar cells. The ZnS-coating depths on TiO2 in this system were found to be easily controlled in nano-scale by adjusting the amount of reactants and/or the sonication time. The ZnS-coated TiO2 nanoparticles were characterized by XRD, UV–vis, EDS, and HR-TEM.

Emission from Electronically Excited Metal Atoms during Single-Bubble Sonoluminescence

Variations in sonoluminescence (SL) from an acoustically driven but rapidly translating bubble in solutions of sulfuric acid with alkali-metal salts coincide with variations in translational bubble dynamics. At low acoustic pressures, emission from Ar excited states is observed and the bubble motion is smooth and elliptical. At elevated acoustic pressures, SL intensity decreases, emission from excited alkali-metal atoms is observed, and the bubble motion becomes increasingly erratic with frequent and abrupt changes in direction. These results provide a direct experimental link between single and multibubble SL and point toward the origins of sonochemical reactivity of nonvolatile species.

Experimental and theoretical investigations on sonoluminescence under dual frequency conditions

The multibubble sonoluminescence (MBSL) intensities from water exposed to the simultaneous ultrasonic irradiation from 20kHz (fixed at 6.3W) and 355kHz (variable power) ultrasound sources have been compared to the MBSL from the individual ultrasound sources under the same power conditions. A synergistic enhancement of the sonoluminescence (SL) signal, >30-fold, at low powers (4.6W) of the higher frequency was observed. At a higher acoustic power level (15.8W) the dual frequency operation produced a decrease in the SL signal. These results are in agreement with previously reported data [P. Ciuti, N.V. Dezhkunov, A. Francescutto, F. Calligaris, F. Sturman, Ultrasonics Sonochem. 10 (2003) 337; N.V. Dezhkunov, J. Eng. Phys. Therm. 76 (2003) 142] under similar experimental conditions. Numerical single bubble (SB) dynamics calculations have been used to help interpret the experimental results. It is suggested that the observed effects are caused by a combination of changes to the peak collapse temperature of individual bubbles as well as to changes in the active bubble population.

Inversion of the relative probabilities of the f-f and f-d transitions in the Ln3+ lanthanide ions at their radio- and sonoexcitation as compared to photoexcitation

The results of measuring the efficiencies of the formation of electronically excited states of the Ln3+ lanthanide ions in aqueous solutions in the processes of radioluminescence and multibubble sonoluminescence are analyzed. In both cases, electronic excitation occurs due to inelastic collisions of Ln3+ ions with (for radioluminescence) charged ionizing particles in liquid and (for multibubble sonoluminescence) high-energy particles, primarily electrons, in the gas phase of cavitation bubbles. In both processes, the efficiencies of exciting ions whose luminescence states appear in the 4f-5d transitions (Ce3+ and Pr3+) are significantly lower (by an order of magnitude or larger) than the efficiencies of exciting ions whose luminescence states appear in the 4f-4f transitions (Gd3+ and Tb3+). Therefore, the probability of the f-d transitions is lower than the probability of the f-f transitions in lanthanide ions excited by collisions with the charged particles and the relative probabilities of these transitions are inverted in these processes as compared to photoexcitation.

Multibubble Sonoluminescence and Na Atom Emission in Sodium Dodecyl Sulfate Surfactant Solutions

Multibubble sonoluminescence spectra were measured in sodium dodecyl sulfate (SDS) solutions at the frequencies of 108 kHz and 1.0 MHz. At 108 kHz under a low power, the total sonoluminescence intensity is enhanced and reaches a maximum at 1 mM. At 108 kHz under a high power, the sonoluminescence intensity gradually decreases in the SDS concentration range of 0.1–100 mM, whereas at 1.0 MHz, the sonoluminescence intensity is rapidly quenched at a concentration of 1 mM and increases afterward. Na D-line peaks at 589 nm were observed at both frequencies for concentrations above 0.5 mM. Na atom emission is more prominent at 1.0 MHz than at 108 kHz. The frequency effect is discussed in terms of rectified diffusion including dynamic equilibrium isotherm for the surface excess of surfactant and the production of OH radicals.

Sonoluminescence of elementary sulfur melt

The sonoluminescence of liquid sulfur has been observed for temperatures of 120–180°C. The sonoluminescence intensity of the sulfur melt is 109 photons/s at 120°C. As the temperature increases, the luminescence intensity decreases nonmonotonically, a maximum is observed at 160–175°C, and cavitation and luminescence cease at 180°C. The dependence obtained correlates with the temperature dependence of the viscosity of the sulfur melt. The sonoluminescence spectrum obtained with a resolution of 10 nm for 130–150°C contains one band with λmax = 560 nm, the emitter of which is likely an (S+)* ion. When the melt is saturated with argon, the sonoluminescence intensity increases by an order of magnitude; in this case, the spectral band shape changes only slightly. The results confirm the “electric” theory of multibubble sonoluminescence. In the process of the sonolysis of the sulfur melt, biradical fragments are formed in cavitation bubbles consisting of sulfur molecules, which initially have the form of cyclooctasulfur S8. These fragments can enter into the melts and can be involved in various chemical reactions. This circumstance makes it possible to recommend ultrasonic activation for reactions of sulfurization of hydrocarbons.

Syntheses of ZnO and ZnO-coated TiO2 nanoparticles in various alcohol solutions at multibubble sonoluminescence (MBSL) condition

Abstract Syntheses of zinc oxide (ZnO) and ZnO-coated titanium dioxide nanoparticles under ultrasonic field at the multibubble sonoluminescence (MBSL) condition were tried in various alcohol solutions. The MBSL condition facilitates the supercritical state of liquid layer where high-energy chemical reaction in the layer around the bubble is possible. At the optimal MBSL condition in alcohol solutions containing zinc acetate dihydrate of 2.75 wt%, sodium hydroxide of 1 wt% and TiO 2 of 1 wt%, ZnO nanoparticles having the average diameter of 7 nm were synthesized first and subsequently ZnO-coated TiO 2 nanoparticles were synthesized within 10 min. The prepared particles of ZnO and ZnO-coated TiO 2 were examined by XRD, UV–vis spectrophotometer and HR-TEM.

Shape stability and violent collapse of microbubbles in acoustic traveling waves

Acoustically driven bubbles can develop shape instabilities and, if forced sufficiently strongly, distort greatly and break up. Perturbation theory provides some insight as to how these nonspherical shape modes grow initially but loses validity for large deformations. To validate the perturbation theory, we use a numerical model based on the boundary integral method capable of simulating nonspherical, axisymmetric bubbles subject to acoustic driving. The results show that the perturbation theory compares well with numerical simulations in predicting bubble breakup and stability. Thereafter, we compare the peak temperatures and pressures of spherical to nonspherical bubble collapses by forcing them with standing waves and traveling waves, respectively. This comparison is made in parameter ranges of relevance to both single bubble sonoluminescence and multibubble sonoluminescence and sonochemistry. At moderate forcing, spherical and nonspherical collapses achieve similar peak temperatures and pressures but, as the forcing is increased, spherical collapses become much more intense. The reduced temperature of nonspherical collapses at high forcing is due to residual kinetic energy of a liquid jet that pierces the bubble near the time of minimum volume. This is clarified by a calculation of the (gas) thermal equivalent of this liquid kinetic energy.

Sonoluminescence, sonochemistry (H 2O 2 yield) and bubble dynamics: Frequency and power effects

In the present work, comprehensive experimental and numerical investigations on the effects of ultrasound frequency and acoustic power on sonoluminescence (SL) and H 2O 2 yields have been carried out. The multibubble SL and H 2O 2 yields have been examined for four frequencies (213, 355, 647 and 1056 kHz) and over a wide range of acoustic powers. The observed experimental results have been discussed with respect to single bubble dynamics and the number of active cavitation bubbles.

Evidence for a Plasma Core during Multibubble Sonoluminescence in Sulfuric Acid

Multibubble sonoluminescence arises from the cavitation of bubbles owing to high-intensity ultrasonic irradiation of liquids. The spectrum of multibubble sonoluminescence in concentrated sulfuric acid sparged with Ar, at relatively low acoustic power, consists of a broad continuum extending into the UV with SO and Ar emission lines on top of this continuum. The observation of the Ar lines indicates that an optically opaque plasma is probably generated inside the bubble during cavitation. There are three distinct light-emitting morphologies for multibubble sonoluminescence from an ultrasonic horn; as the acoustic intensity is increased, the emission changes from filamentous, to bulbous, to cone shaped, and it is only from the filamentous emission that strong atomic and molecular emissions are observed.

Bubbles in an acoustic field: An overview

Acoustic cavitation is the fundamental process responsible for the initiation of most of the sonochemical reactions in liquids. Acoustic cavitation originates from the interaction between sound waves and bubbles. In an acoustic field, bubbles can undergo growth by rectified diffusion, bubble–bubble coalescence, bubble dissolution or bubble collapse leading to the generation of primary radicals and other secondary chemical reactions. Surface active solutes have been used in association with a number of experimental techniques in order to isolate and understand these activities. A strobe technique has been used for monitoring the growth of a single bubble by rectified diffusion. Multibubble sonoluminescence has been used for monitoring the growth of the bubbles as well as coalescence between bubbles. The extent of bubble coalescence has also been monitored using a newly developed capillary technique. An overview of the various experimental results has been presented in order to highlight the complexities involved in acoustic cavitation processes, which on the other hand arise from a simple, mechanical interaction between sound waves and bubbles.

2-07-02 Multi-Bubble Sonoluminescence and Bubble Dynamics with Burst-type Ultrasound(Sonochemistry)

2-07-02 Multi-Bubble Sonoluminescence and Bubble Dynamics with Burst-type Ultrasound(Sonochemistry)

Comparison of sonoluminescence and water vapor plasma spectra

An experimental study was carried out to find the mechanism of OH spectra generation through sonoluminescence. Line spectra of OH, H, and O were observed very clearly in water vapor plasma generated by 2.45-GHz microwave irradiation under the pressure of 40 hPa; however, broadband continua were not detected. Multibubble sonoluminescence (MBSL) and single-bubble sonoluminescence (SBSL) have continua, and OH spectra were detected occasionally in MBSL. However, OH spectra were not detected in SBSL and higher temperature MBSL. The sources of emission in MBSL and SBSL were considered to be identical and differences in spectra of OH bands were attributable to the higher temperature. Experimental results obtained using low temperature water vapor plasma confirm that OH spectra depend on the bubble’s interior plasma temperature: that is, at low temperatures, spectra of OH (308 nm), Ha, Hb, and O are clearly visible in water vapor plasma.

Frequency effects on intense sonoluminescence and bubble dynamics in sulfuric acid

Emission intensity increased remarkably with decreasing frequency for both multibubble sonoluminescence (MBSL) and single-bubble sonoluminescence (SBSL) in a concentrated sulfuric acid solution dissolving xenon gas. The spectrum of MBSL in the sulfuric acid showed the emission bands of a large peak at 388 nm and small peaks at 360 and 418 nm. The increase of MBSL intensity at lower frequency was responsible for the increase of the band peak at 388 nm in addition to the increase in continuous spectrum. The bubble dynamics in the sulfuric acid was different from that in water. The intense SBSL was emitted when the bubble was moving on an ellipselike trajectory. The intense MBSL was emitted even when multiple bubbles formed bubble clusters, which could not emit light in the water case.

On the mechanism of multi-bubble sonoluminescence

The thermal chemiluminescent model of multibubble sonoluminescence (MBSL) is considered, and the contradictions that follow from its basic propositions are analyzed. It is shown that, if the thermal mechanism of sonoluminescence (SL) is operative, the continuous spectrum should be emitted before the band spectrum. It is established that, if the thermal recombination mechanism of a solid is operative, the duration of SL should be at least two orders of magnitude longer than that observed experimentally (<5 ns); according to the chemiluminescent model of SL, the SL burst time must be several orders of magnitude longer. Consideration is given to the previously proposed mechanism of emission of spectral lines of metals from solutions of alkali and alkaline-earth metal salts, which correlates with results of sonolysis of salt solutions under the action of ultrasound (US) pulses. A mechanism based on the theory of local electrification of cavitation bubbles in the US field is put forward to treat MBSL. It is shown that this mechanism agrees with experimental results: the SL burst time corresponds to the characteristic time of fluorescence.