Sonochemiluminescence Intensity Research Articles

New sonochemiluminescence involving solvated electron in Ce(III)/Ce(IV) solutions

The moving single-bubble sonoluminescence of Ce3+ in water and ethylene glycol solutions of CeCl3 and (NH4)2Ce(NO3)6 was studied. As found, a significant part of intensity of the luminescence (100% with cerium concentration less than 10–4 M) is due to the sonochemiluminescence. A key reaction of sonochemiluminescence is the Ce4+ reduction by a solvated (or hydrated in water) electron: Ce4+ + es (eaq) → *Ce3+. Solvated electrons are formed in a solution via electrons ejection from a low-temperature plasma periodically generated in deformable moving bubble at acoustic vibrations. Reactions of heterolytic dissociation of solvents make up the source of electrons in the plasma. In aqueous CeCl3 solutions, the Ce4+ ion is formed at the oxidation of Ce3+ by OH radical. The latter species originates from homolytic dissociation of water in the plasma of the bubble, also penetrating from the moving bubble into the solution. The sonochemiluminescence in cerium trichloride solutions are quenched by the Br− (acceptor of OH) and H+ ions (acceptor of eaq). In water and ethylene glycol solutions of (NH4)2Ce(NO3)6, the sonochemiluminescence also quenched by the H+ ion. The sonochemiluminescence in CeCl3 solutions is registered at [Ce3+] ≥ 10–5 M. Then the sonochemiluminescence intensity increases with the cerium ion concentration and reaches the saturation plateau at 10–2 M. It was shown that sonophotoluminescence (re-emission of light of bubble plasma emitters by cerium ions) also contributes to the luminescence of Ce3+ in solutions with [Ce3+] ≥ 10–4 M. If the cerium concentration is more than 10–2 M, a third source contributes to luminescence, viz., the collisional excitation of Ce3+ ions penetrating into the moving bubble.

Sonochemiluminescence of lucigenin using amines as coreactant: Reactivity and mechanism studies

Sonochemiluminescence (SCL) from aqueous solution of lucigenin (Luc2+) has been studied using aliphatic amines as coreactant. The SCL intensity are strongly dependent on the dissolved gases such as air, oxygen, nitrogen and argon. The most strong SCL signals are observed from oxygen saturated alkaline solution containing Luc2+ when small amount of trialkylamine, such as tripropylamine (TPrA) was added into the solution. In an ultrasonic field, TPrA can adsorb onto the cavitation bubble/solution interface where TPrA is oxidized by OH to form a radical cation TPrA+ and subsequently produce a highly reducing TPrA species through a deprotonation reaction of the TPrA+. TPrA is suggested to initiate the reduction reactions of Luc2+ and molecule oxygen to produce Luc+ and superoxide radical anion (O2−), respectively. The radical-radical coupling reaction between Luc+ and O2− is expected to initiate the light emission. The production of O2− is examined by spectrofluorometric method using 2-(2-pyridyl)benzothiazoline as a fluorescent probe. The results show that the production of O2− by ultrasound was more efficient in oxygen saturated solution in the presence of coreactants, consistent with the results with SCL measurements.

Ultrasonic degradation of perfluorooctane sulfonic acid (PFOS) correlated with sonochemical and sonoluminescence characterisation.

Sonolysis has been proposed as a promising treatment technology to remove per- and polyfluoroalkyl substances (PFASs) from contaminated water. The mechanism of degradation is generally accepted to be high temperature pyrolysis at the bubble surface with dependency upon surface reaction site availability. However, the parametric effects of the ultrasonic system on PFAS degradation are poorly understood, making upscale challenging and leading to less than optimal use of ultrasonic energy. Hence, a thorough understanding of these parametric effects could lead to improved efficiency and commercial viability. Here, reactor characterisation was performed at 44, 400, 500, and 1000kHz using potassium iodide (KI) dosimetry, sonochemiluminescence (SCL), and sonoluminescence (SL) in water and a solution of potassium salt of PFOS (hereafter, K-PFOS). Then the degradation of K-PFOS (10mg L-1 in 200mL solution) was investigated at these four frequencies. At 44kHz, no PFOS degradation was observed. At 400, 500, and 1000kHz the amount of degradation was 96.9, 93.8, and 91.2%, respectively, over four hours and was accompanied by stoichiometric fluoride release, indicating mineralisation of the PFOS molecule. Close correlation of PFOS degradation trends with KI dosimetry and SCL intensity was observed, which suggested degradation occurred under similar conditions to these sonochemical processes. At 1000kHz, where the overall intensity of collapse was significantly reduced (measured by SL), PFOS degradation was not similarly decreased. Discussion is presented that suggests a hydrated electron degradation mechanism for PFOS may occur in ultrasonic conditions. This mechanism is a novel hypothesis in the field of PFAS sonolysis.

Sonochemiluminescence of Ru(bpy)33+ in aqueous solutions. Evidence of the formation of hydrated electrons during the single-bubble sonolysis in a neutral aqueous medium.

Consideration is given to single and multibubble sonochemiluminescence (SCL) in acidic Ru(bpy)33+ aqueous solutions due to the light emission of the excited ion *Ru(bpy)32+ at 613 nm. Spectrophotometrically controlled reduction of Ru(bpy)33+ to Ru(bpy)32+ occurs in both regimes of sonolysis. The kinetics parameters of reduction under SCL during the multibubble sonolysis do not depend on the H+ concentration in the solution (0.005 and 0.5 M H2SO4), but differ for the single-bubble sonolysis. The intensity of single-bubble SCL is maximal at the beginning of sonolysis and monotously decreases to the level of steady-state SCL after complete reduction of Ru(bpy)33+ to Ru(bpy)32+. The intensity of multibubble SCL at the beginning of sonolysis is below the recognition threshold. Then it grows, passes through the maximum and also approaches the steady-state level after the reduction of ruthenium. By considering possible chemiluminescent reactions Ru(bpy)33+ + eaq → *Ru(bpy)32+, Ru(bpy)33+ + H → *Ru(bpy)32+ + H+, Ru(bpy)33+ + Ru(bpy)3+ → *Ru(bpy)32+ + Ru(bpy)32+ as well as the reactions of sonochemical formation of Ru(bpy)33+ and Ru(bpy)3+ from Ru(bpy)32+ and the reaction H+ + eaq → H, the conclusion is made about the generation of eaq during the single-bubble sonolysis of water molecules. The presence and absence of eaq during the single and multibubble sonolysis respectively explain the distinctions in the SCL kinetics. The evidence for the generation of eaq lies also in the reduction of the Fe(CN)63- ion observed during the single-bubble sonolysis in the neutral solution, which is impossible without eaq. The yield of eaq is comparable to that of the hydrogen atom.

Disparities between sonoluminescence, sonochemiluminescence and dosimetry with frequency variation under flow.

The effects of ultrasound (frequency and pressure amplitude) and external parameters (fluid flow rate and surface stabilisation) on active sonoluminescence (SL) and sonochemical (SC) bubbles were investigated using common characterisation techniques. The SL from water, sonochemiluminescence (SCL) from luminol solutions and iodide dosimetry were studied at flow rates of 0, 24, 228 and 626 mL/min at 44, 300 and 1000 kHz with and without surface stabilisation. An increase in flow, in general, decreased SL, SCL and dosimetry caused by a reduction in collapse intensity. However, all flow rates were also able to increase SL intensity and the highest flow rate (626 mL/min) could also increase SCL and dosimetry. For SL, augmentation with flow was attributed to a reduction in coalescence bubbles which cause growth to inactive size (44 kHz) and enhancement of the standing wave at the surface of solution (300 and 1000 kHz). Where agitation at the solution surface (44 kHz) caused aeration (without stabilisation), flow may have circulated additional cavitation nuclei, increasing SL. Increases in SCL intensity and dosimetry yields were attributed to increased bubble fragmentation which was more influential for the latter process. Disparities between SCL and dosimetry are discussed in terms of gas concentration and reaction energy requirements influenced by the transient nature of the bubbles. SL and SCL had complimentary behaviour when they were located in the same regions i.e. a reduction in SL resulted in an increase in SCL as bubbles moved from stable to transient in nature. The same was not observed when SL and SCL bubbles were located in different regions. The active region for SL/SCL could differ or overlap, depending on the standing to travelling wave proportions at each frequency effecting active regions. In some cases, increased standing wave proportions throughout the reactor (with surface stabilisation) did not facilitate an increase in SL intensity, as was expected. Here, the travelling wave without stabilisation enabled a stronger area of activity toward the surface with a localised standing wave.

Cavitational activity in heterogeneous systems containing fine particles.

Ultrasound has been increasingly used in various processes containing a variety of homogeneous and heterogeneous systems. For largescale applications, a high energy efficiency of the process is required. With this view, the calorimetric energy and cavitational activity measurements were carried out in heterogeneous systems consisting of both liquid and solid phases (fine particles) in a 28-kHz double-bath sonoreactor. Ultrasonic soil washing for the remediation of clay-sized soils (∼75 µm), contaminated with metals (Cu, Pb, and Zn), was used as a case study. As the liquid height/volume in the inner vessel increased under the same input electrical power, the inner vessel calorimetric energy also increased, whereas the total calorimetric energy between the inner vessel and the outer reactor remained approximately constant. No significant differences in calorimetric energies were observed for both with and without soil conditions. The chemical activity under similar experimental conditions was evaluated using sonochemiluminescence. Different sonochemiluminescence trends were observed depending up on the presence and size of beads. The highest total sonochemiluminescence intensity with a uniform spatial distribution was obtained from fine beads (#200, 75 µm) suspended in the vessel. Ultrasound application significantly enhanced the removal efficiency of heavy metals when combined with mechanical agitation. The enhanced removal efficiency of the combined processes was attributed to a significant removal of metals from the residual (F5) fraction. It has been concluded that ultrasound has enough extraction power to be comparable to methods that employ extremely powerful acids for washing fine particles.

Activation of Ru(bpy)32+ multibubble sonochemiluminescence in alkaline aqueous solutions by a hydrated electron

The sonochemiluminescence in 10−4 M aqueous solutions of Ru(bpy)3Cl2 was studied in the presence of NaOH and KOH (up to 0.4 M). The observed increase in the steady-state emission intensity from Ru(bpy)32+ as compared with the intensity in neutral solutions was attributed to conversion of H resulting from water sonolysis to eaq. As a result, there is a multiple (>106) change in the concentrations of the sonochemical intermediates Ru(bpy)3+ and Ru(bpy)33+. The reduction of the Ru(bpy)33+ ion with H, which is of low efficiency for the formation of the excited *Ru(bpy)32+ ion, is replaced by reduction with hydrated electron, in which *Ru(bpy)32+ is generated in a high yield. The participation of eaq provides a fivefold increase in the sonochemiluminescence intensity in a key disproportionation reaction: Ru(bpy)3+ + Ru(bpy)33+ → Ru(bpy)32+ + *Ru(bpy)32+. It was shown that chemiluminescence from reduction of intermediate Ru(bpy)33+ with the OH− ion does not make a pronounced contribution to the sonochemiluminescence intensity.

Sonochemiluminescence of lucigenin: Evidence of superoxide radical anion formation by ultrasonic irradiation

The sonochemiluminescence (SCL) behavior of lucigenin (Luc2+) has been studied in aqueous solutions irradiated with 500 kHz ultrasound. Compared with the SCL of a luminol system, a tremendously increased SCL intensity is observed from 50 µM Luc2+ aqueous solution (pH =11) when small amounts of coreactants such as 2-propanol coexist. It is shown that SCL intensity strongly depends on the presence of dissolved gases such as air, O2, N2, and Ar. The highest SCL intensity is obtained in an O2-saturated solution, indicating that molecular oxygen is required to generate SCL. Since SCL intensity is quenched completely in the presence of superoxide dismutase (SOD), an enzyme that can catalyze the disproportionation of O2•−, the generation of O2•− in the ultrasonic reaction field is important in the SCL of Luc2+. In this work, the evidence of O2•− production is examined by a spectrofluorometric method using 2-(2-pyridyl)benzothiazoline as the fluorescent probe. The results indicate that the yield of O2•− is markedly increased in the O2-saturated solutions when a small amount of 2-propanol coexists, which is consistent with the results of SCL measurements. 2-Propanol in the interfacial region of a cavitation bubble reacts with a hydroxyl radical (•OH) to form a 2-propanol radical, CH3C•(OH)CH3, which can subsequently react with dissolved oxygen to generate O2•−. The most likely pathways for SCL as well as the spatial distribution of SCL in a microreactor are discussed in this study.

Sonoluminescence and sonochemiluminescence of peroxide solutions

Two sonochemiluminescence mechanisms were established in peroxide solutions. The sonochemiluminescence intensity often exceeds the sonoluminescence intensity of solvents caused by inelastic collisions of cavitation bubbles in the gas phase. In solutions of peroxides, whose chemiluminescence decomposition proceeds via the monomolecular peroxide decomposition involving no radical intermediates with a high activation energy, in particular, for adamantylidenadamantane-1,2-dioxetane, the mechanism based on the total thermal ultrasonic action on the solution takes place. The initiation of chemiluminescence reactions of peroxide decomposition by radical products of solvent sonolysis is a source of sonochemiluminescence for peroxides decomposing via the radical mechanism, for example, for cumene peroxide.

Sono-chemiluminescence (SCL) in a high-pressure double stage homogenization processes

An applied back-pressure to a high pressure homogenization system influences the development of hydrodynamic cavitation and the collapse of cavitation bubbles. This paper focuses on the effect of back-pressure on hydrodynamic cavitation and how the intensity of collapsing cavitation bubbles can be identified. Based on sono-chemiluminescence (SCL), an optical measuring method was developed to detect cavitation induced formation of •OH radicals, which indicates the intensity of collapsing cavities. The results are discussed with the introduced dimensionless SCL intensity number I¯SCL. The I¯SCL number increases with increasing inlet pressure as well as with increasing back-pressure and confirms therewith theoretical based assumptions by other studies. A maximum I¯SCL at a back-pressure of approximately 30% was found and reduced to an intensified collapse of cavities in or after the first high pressure disruption unit. The maximum in SCL intensity is in line with the minimum droplet size of corresponding emulsification experiments.

초음파 수처리 공정 개발을 위한 반응기 설계 기초 연구

본 연구는 환경, 에너지, 재료 등 다양한 분야에 적용할 수 있는 초음파 기술을 수처리 공정에 적용하기 위한 기초 연구로 수행되었다. 초음파 기술과 같은 고도산화처리공법은 중금속, 내분비계장애물질, 의약물질 등의 미량오염물질 처리에 효과적이어서 하천, 호소, 습지의 수질 향상에 크게 기여할 수 있을 것으로 기대되고 있다. 초음파 기술은 파를 기반으로 하기 때문에 본 연구에서는 적용 주파수의 파장을 이용하여 <TEX>$0{\sim}4{\lambda}$</TEX> 구간의 수위를 <TEX>$1/4{\lambda}$</TEX> 간격으로 나누어 동일한 유입에너지 조건에서 발생하는 열에너지 및 초음파 캐비테이션의 화학적 효과를 정량화 하였다. 실험 결과 낮은 수위 (적은 부피)의 에너지 밀도가 높은 조건보다 높은 수위 (큰 부피)의 에너지 밀도가 낮은 조건에서 열에너지 및 화학적 효과가 극대화되는 것을 확인하였다. 이러한 현상을 반응기 내부의 캐비테이션 활성도 시각화를 통해 알아본 결과, 높은 수위 (큰 부피) 조건에서는 에너지 밀도가 낮음에도 불구하고 반응기 전체적으로 높은 활성도를 얻을 수 있기 때문인 것으로 확인되었다. 따라서 본 연구결과를 이용하여 초음파 기술을 수처리 분야에 적용할 경우 반응성 및 에너지 효율 측면에서 적용 가능성을 보다 높일 수 있을 것으로 예상된다. Ultrasound technology can be applied in various fields including environmental, energy, and material engineering processes. In this study the effect of liquid height/volume on calorimetric energy and sonochemical oxidation was investigated as one of the basic steps for the design of water/wastereater treatment sonoreactors. The liquid height was increased from 0 to <TEX>$4{\lambda}$</TEX> by <TEX>$1/4{\lambda}$</TEX> and it was found that both calorimetric energy and sonochemical oxidation were significantly increased at relatively high liquid height/volume where the power density was relatively low. The sonochemiluminescence (SCL) images for the visualization of the activity of cavitation also showed that larger and more stable active zone was formed with high SCL intensity at high liquid height/volume. Therefore, it was revealed that sonoreactors for water/wasterwater treatment could be significantly effective in terms of removal efficiency and energy consumption.

Cavitation mapping by sonochemiluminescence with less bubble displacement induced by acoustic radiation force in a 1.2 MHz HIFU

An acoustic radiation force counterbalanced appliance was employed to map the cavitation distribution in water. The appliance was made up of a focused ultrasound transducer and an aluminum alloy reflector with the exactly same shape. They were centrosymmetry around the focus of the source transducer. Spatial–temporal dynamics of cavitation bubble clouds in the 1.2MHz ultrasonic field within this appliance were observed in water. And they were mapped by sonochemiluminescence (SCL) recordings and high-speed photography. There were significant differences in spatial distribution and temporal evolution between normal group and counterbalanced group. The reflector could avoid bubble directional displacement induced by acoustic radiation force under certain electric power (⩽50W). As a result, the SCL intensity in the pre-focal region was larger than that of normal group. In event of high electric power (⩾70W), most of the bubbles were moving in acoustic streaming. When electric power decreased, bubbles kept stable and showed stripe structure in SCL images. Both stationary bubbles and moving bubbles have been captured, and exhibited analytical potential with respect to bubbles in therapeutic ultrasound.

Influence of Degree of Gas Saturation on Sonochemiluminescence Intensity Resulting from Microfluidic Reactions

This work examined the effects of dissolved gas degree of saturation (DOS) on sonochemical reaction yields in both a one-dimensional (1D) microspace and a three-dimensional (3D) millimeter-sized space. The extent of each reaction was monitored by measuring sonochemiluminescence (SCL) intensity at 213 kHz. The results demonstrated that, at relatively low levels of power density, selecting a solution DOS in the supersaturation range at atmospheric pressure resulted in higher yields per unit volume in the 1D space compared to that obtained from the 3D space. This effect is attributed to a decrease in the cavitation threshold of the 1D reaction system since, at low power density, the 1D space represents a more homogeneous reaction volume. Comparing the highest SCL intensity levels obtained from the 3D and 1D reactions shows that enhancing the reaction yield in the 1D space requires higher DOS values than are required to generate elevated yields in the 3D space. The 3D space contains a greater concentration of bubbles than the 1D space, but many of these are ineffective at promoting the reaction. Thus, reactions in the 3D environment require not only the application of higher power density levels but also a lower DOS, so as to allow the bubbles to undergo the violent pulsations necessary to facilitate the sonochemical reaction.

Surface vibration and nearby cavitation of an ex vivo bovine femur exposed to high intensity focused ultrasound

The acoustic pressure distribution, thermal ablation, and sonochemiluminescence (SCL) generated by cavitation near the surface of an ex vivo bovine femur were investigated at normal and oblique incidences of high intensity focused ultrasound (HIFU), as were the characteristics of bone surface vibrations. The acoustic pressure at the HIFU focus, the width of thermal ablation, and the SCL intensity in the pre-focal region were 1.3 MPa, 7 mm, and 454 electrons, respectively, in the control group at normal incidence, and they respectively increased to 1.5 MPa, 12 mm and 968 electrons in the presence of the bone. At oblique incidence from the left, the acoustic pressure at 3 mm to the right of the HIFU focus was 0.6 MPa and decreased to 0.4 MPa at 3 mm to the left of the focus. The thermal ablation was 20 mm in width and extended along the front surface of the bone to the right of the HIFU focus. The SCL intensity on the right of the HIFU focus was 394 electrons and was 362 electrons on the left. The presence of bone would directionally change the spatial distribution of acoustic pressure, thermal and cavitation effects for oblique incidence of HIFU.

Sonochemiluminescence observation and acoustic detection of cavitation induced by pulsed HIFU at a tissue–fluid interface

The aim of this study is to investigate the mechanism of the erosion process induced by 1.2MHz pulsed high-intensity focused ultrasound (pulsed HIFU). By using Sonochemiluminescence (SCL) photograph, the initiation and maintenance of active cavitation were observed. In order to understand the role of both inertial cavitation and stable cavitation, a passive cavitation detection (PCD) transducer was used. Since the exposure variables of HIFU are important in the controlled ultrasound tissue erosion, the influence of pulse length (PL) and duty cycle (DC, Ton:Toff) has been examined. The results of tissue hole, SCL observation and acoustic detection revealed that the erosion was highly efficient for shorter PL. For higher DCs, the area of SCL increased with increasing PL. For lower DCs, the area of SCL increased with increasing PL from 10 to 20μs and then kept constant. For all PLs, the intensity of SCL decreased with lower DC. For all DCs, the intensity of SCL per unit area (the ratio of SCL intensity to SCL area) also decreased with increasing PL from 10 to 80μs, which suggested that the higher the intensity of SCL is, the higher the efficiency of tissue erosion is. At DC of 1:10, the position of the maximum pixel in SCL pictures was distant from the tissue–fluid interface with the increasing PL because of shielding effect. By the comparison of inertial cavitation dose (ICD) and the stable cavitation dose (SCD), the mechanisms associated with inertial cavitation are very likely to be the key factor of the erosion process.

Sonochemiluminescence observation of lipid- and polymer-shelled ultrasound contrast agents in 1.2 MHz focused ultrasound field

Ultrasound contrast agents (UCAs) are frequently added into the focused ultrasound field as cavitation nuclei to enhance the therapeutic efficiency. Since their presence will distort the pressure field and make the process unpredictable, comprehension of their behaviors especially the active zone spatial distribution is an important part of better monitoring and using of UCAs. As shell materials can strongly alter the acoustic behavior of UCAs, two different shells coated UCAs, lipid-shelled and polymer-shelled UCAs, in a 1.2MHz focused ultrasound field were studied by the Sonochemiluminescence (SCL) method and compared.The SCL spatial distribution of lipid-shelled group differed from that of polymer-shelled group. The shell material and the character of focused ultrasound field work together to the SCL distribution, causing the lipid-shelled group to have a maximum SCL intensity in pre-focal region at lower input power than that of polymer-shelled group, and a brighter SCL intensity in post-focal region at high input power. The SCL inactive area of these two groups both increased with the input power. The general behavior of the UCAs can be studied by both the average SCL intensity and the backscatter signals. As polymer-shelled UCAs are more resistant to acoustic pressure, they had a higher destruction power and showed less reactivation than lipid-shelled ones.

Acoustic, thermal and sonoluminescence investigation of enhanced cavitation of flowing polymer- and lipid-shelled microbubbles during focused ultrasound exposures

Our previous work has investigated spatial-temporal dynamics of cavitation during focused ultrasound (FU) exposures using acoustic cavitation detection and high-speed photography. In this paper, acoustic, thermal and sonoluminescence investigation of enhanced cavitation of flowing polymer- and lipid-shelled microbubbles (MBs) during FU exposures were exposed as the two types of shelled MBs and pure controls flowing through a vessel in the phantom with varying flow velocities at different acoustic power levels. Vibration characteristics of two shelled MBs and the effects of acoustic pressure threshold for destruction of the two shelled MBs on the intensity and spatial distribution of sonoluminescence and sonochemiluminescence were investigated using an electron-multiplying charge coupled device camera. The inertial cavitation dose (ICD), sonochemiluminescence intensity and temperature for the lipid-shelled MBs were higher than those for the polymer-shelled MBs, which were both higher than pure controls. Te...

Spatial distribution of sonoluminescence and sonochemiluminescence generated by cavitation bubbles in 1.2 MHz focused ultrasound field

An intensified charge coupled device (ICCD) camera was used to observe the spatial distribution of sonoluminescence (SL) and sonochemiluminescence (SCL) generated by cavitation bubbles in a 1.2 MHz focused ultrasound (FU) field in order to investigate the mechanisms of acoustic cavitation under different sonication conditions for FU therapeutic applications. It was found that SL emissions were located in the post-focal region. When the intensity of SL and SCL increased as the power rose, the growth of SCL was much higher than that of SL. In the post-focal region, the SCL emissions moved along specific paths and formed branch-like streamers. At the beginning of the ultrasound irradiation, cavitation bubbles generated SCL in both the pre-focal and the post-focal region. When the electrical power or the sonication time increased, the SCL in the post-focal region increased and became higher than that in the pre-focal region. The intensity of SCL in the focal region is usually the weakest because of “oversaturation”. The spatial distribution of SCL near a tissue boundary differed from that obtained in free fields. It organized into special structures under different acoustic amplitudes. When the electrical power was relatively low, the SCL emission was conical shape which suggested a standing wave formation at the tissue–fluid boundary. When the electrical power exceeded a certain threshold, only a bright spot could be captured in the focus. The cavitation bubbles which centralized in the focus concentrated energy and hindered the formation of standing waves. With rising electrical power at high levels, besides a bright spot in the focus, there were some irregular light spots in pre-focal region, which indicated some cavitation bubbles or small bubble clusters achieved the threshold of SCL and induced the reaction with the luminol solution.

Influence of Liquid-Surface Vibration on Sonochemiluminescence Intensity

The influence of surface vibrations on the intensity of sonochemiluminescence (SCL) produced by pulsed ultrasound with a frequency of 151 kHz is investigated through optical measurement of the vibration amplitude. Pulsed ultrasound inhibits the generation of large degassing bubbles that scatter sound waves, thereby restricting the effective spatial region for sonochemical reactions. The vibration amplitude of the liquid surface becomes gradually significant with pulsed ultrasound as the power applied to the transducer increases. At this time, the SCL intensity increases and then decreases after displaying a peak because the resonance of standing wave cannot be maintained stably by the surface vibration. The SCL intensity during high-amplitude pulsing becomes almost zero if the distance between the highest position of the liquid surface and its position in the absence of ultrasound becomes close to larger than one-quarter of the ultrasound wavelength. This condition for the liquid surface vibration provides a limit for establishment of a resonant standing wave that is effective for sonochemical reaction. Adding particles provides nucleation sites for cavitation bubbles, thereby inhibiting the vibration of the surface of the upper liquid level. The SCL intensity is enhanced by the addition of alumina particles under pulsed excitation at relatively low applied powers.

Suppression of Sonochemiluminescence Reduction at High Acoustic Amplitudes by the Addition of Particles

The effect of particle addition to a liquid or liquid surface on the sonochemiluminescence (SCL) was investigated using a luminol aqueous solution under ultrasonic treatment at 154 kHz. The acoustic-amplitude dependence of the SCL intensity was measured, in addition to capturing images of luminescent spatial patterns. At higher acoustic amplitudes, the cavitation efficiency dramatically reduces. This behavior is suppressed in the presence of particles. Particle addition provides nucleation sites for cavitation bubbles, lowering the cavitation threshold, and weakening the liquid surface vibration as the pressure amplitude decreases. It is shown that the reduction in SCL is suppressed under the addition of alumina particles into luminol aqueous solution. As the amount of alumina particles increases, the range of acoustic amplitude for suppressing the reduction in SCL is enlarged toward high amplitude, and the intensity of the SCL increases. Simultaneous addition of alumina particles into the solution and hydrophobic polytetrafluoroethylene (Teflon) particles onto the liquid surface is also effective. Examination of SCL images revealed that alumina particles added to the liquid at high acoustic amplitude caused the entire region of the reaction volume to be homogeneously luminous. If hydrophobic particles cover the solution surface, the surface vibration at high acoustic amplitude is fixed and the sound field becomes stable. This is responsible for suppression of the reduction in SCL and leads to a high rate of sonochemical reaction, even at high acoustic amplitude.