Influence of He and Ar Flow Rates and NaCl Concentration on theSize Distribution of Bubbles Generated by Power UltrasoundRachel Pflieger,*,† Judy Lee,‡ Sergey I. Nikitenko,† and Muthupandian Ashokkumar§

†Institut de Chimie Separative de Marcoule (ICSM), UMR 5257 CEA − CNRS − UM − ENSCM, Centre de Marcoule, BP 17171,30207 Bagnols-sur-Ceze Cedex, France‡Chemical and Process Engineering, University of Surrey, Guildford, Surrey GU27XH, U.K.§Particulate Fluids Processing Centre, School of Chemistry, University of Melbourne, Melbourne, VIC 3010, Australia

*S Supporting Information

ABSTRACT: A technique based on pulsed ultrasound and sonoluminescenceemission was used to measure the size and size distribution of bubbles generated by355 kHz power ultrasound under continuous Ar or He flow in aqueous NaClsolutions. It was observed that the bubble size strongly decreased with increasingNaCl concentration and that this decrease was much stronger than in solutionspresaturated with Ar or He. This size decrease is attributed to the combination of thesalting-out effect of the salt and the introduction of bubble nuclei by the continuousgas flow. Besides, the comparison of Ar and He bubbles underlines the effect of thegas diffusion coefficient on the bubble size reached.

1. INTRODUCTION

Sonochemistry is an environmentally friendly area of chemistrythat presents many advantages such as higher mass transfers,lower reaction temperatures, and faster reaction kinetics. Theseadvantages have been beneficially utilized in a variety ofapplications ranging from the synthesis of nanomaterials fortargeted drug delivery applications, food processing, wastewatertreatment, and so forth.1 The origin of sonochemistry isacoustic cavitation, which is the nucleation, growth, and violentcollapse of bubbles in a fluid subjected to ultrasound. Thebubble size and bubble size distribution are key parameters thatinfluence the chemical activity of the system, the dynamics ofthe bubbles, and so forth. Besides, they are input parameters inmost equations describing acoustic cavitation. Therefore,several methods have been developed to measure the bubblesize distribution, for instance, by laser diffraction2 or bymeasuring the dissolution time of sonoluminescence orsonochemically active bubbles under pulsed ultrasound.3

The main parameters that affect the bubble size distributionare basically the same as those that affect the sonochemicalactivity: the nature of solvent and dissolved gas, solutiontemperature, the presence of electrolytes, and so forth.4

Understanding the effect of electrolytes is of particularimportance since they are of concern in most real sonochemicalreactions. In addition, the concentration of dissolved gases issignificantly affected by the quantity of dissolved electrolytes inaqueous solutions, which in turn may control the extent ofcoalescence and the size of bubbles.The effects of these parameters have been investigated in

preliminary studies using a simple sonoluminescence technique

based on the dissolution time of bubbles in a pulsed acousticfield. Bubble size distributions were measured in air-saturatedwater and 1.5 mM SDS at 515 kHz,3 showing that the presenceof SDS resulted in smaller bubbles and a narrower sizedistribution. A similar influence of luminol was observed:5

sonochemically (SC) active bubbles in air-saturated luminolsolution sonicated at 575 kHz (luminol is excited by OH•

radicals created in chemically active bubbles by water sonolysis)were smaller than sonoluminescence (SL) bubbles in water.Besides, the size of SC bubbles decreased with increasingfrequency, and their distribution narrowed. Finally the effect ofthe nature of gas and of the addition of electrolytes (NaCl, KCl,and NaNO3) on the SL bubble size was studied at 515 kHz:4 itwas shown that the bubble size increased from helium to air toargon and decreased when the electrolyte concentration wasincreased, whereby these increases appeared to be correlatedwith a decrease in the solubility of the gases in aqueoussolutions. Bubble coalescence was also shown to decrease uponthe addition of salt, supporting the idea that this mechanismwould be a determinant of the bubble size.Only a very few studies3−6 have been conducted under air or

in solutions saturated with a rare gas. However, many chemicalsyntheses or processes are performed under a continuousbubbling of argon since this usually enhances sonochemicalyields. It is not straightforward that results of studies of Ar-saturated solutions may be extrapolated because continuousbubbling with gas may induce perturbations within the system

Received: September 7, 2015Published: September 10, 2015

Article

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© 2015 American Chemical Society 12682 DOI: 10.1021/acs.jpcb.5b08723J. Phys. Chem. B 2015, 119, 12682−12688

and may introduce a larger number of bubble nuclei. Therefore,the present work aims at expanding the knowledge base onbubble size to the conditions of continuous argon or heliumbubbling. It focuses on the determination of the bubble sizedistribution under Ar and He flow as a function of NaClconcentration at an ultrasonic frequency of 355 kHz using themethod and setup developed in a previous investigation.7

Measurements were performed in water and in 0.1 mM luminolsolutions in order to determine the size distribution of bothsonoluminescence bubbles (in water) and sonochemicallyactive bubbles (in luminol solutions).

2. EXPERIMENTAL DETAILS2.1. Materials. Sodium chloride (ChemSupply, min 97%),

luminol (Sigma-Aldrich, min 97%), and sodium hydroxide(ChemSupply, min 99%) were of analytical grade. Milli-Qwater was used. The pH of 0.1 mM luminol solutions wasadjusted to 12 using sodium hydroxide.2.2. Bubble Size Determinations. Solutions of NaCl 0−5

M were prepared in ultrapure water and in 0.1 mM luminolsolutions and degassed thoroughly under vacuum. Then 200mL of the solution to be sonicated was poured into thesonochemical reactor, consisting of a cylindrical glass reactorwith 6 cm inner diameter attached to the bottom of a high-frequency (355 kHz) piezoelectric transducer (ELAC Nautik,25 cm2). The latter was connected to a high-frequencygenerator (T & C Power Conversion, Inc.) that amplified thesignal of a Hameg function generator (HM8131−2) triggeredby an external pulse generator (Datapulse 100A). The solutionwas sparged with the desired gas (argon or helium, 99.99%,BOC) for at least 10−15 min prior to measurement.Continuous bubbling of the gas at a flow rate of 67 mL/minwas kept during sonication and measurements. Sonication at355 kHz was performed in a pulsed mode with a constant on-time of 4 ms, chosen to be consistent with previous studies,3,5

and a varying off-time (T0). The fixed on-time selected allows asteady-state active bubble population to be reached in water atrelatively short T0. However, at long T0 or at high NaClconcentrations a steady-state active bubble population is notnecessarily reached, as was also observed in an earlier waterstudy.3 The absorbed acoustic power, determined calorimetri-cally in continuous mode, was 33 W. The temperature of thesolution was ∼22 °C.For each pulse off-time, the sonoluminescence, SL (or

sonochemiluminescence, SCL), intensity was measured with aphotomultiplier tube (Hamamatsu, R1463) placed on top ofthe open reactor cell. Due to the much higher sensitivity of thePMT cathode in the 200−500 nm region than at 590 nm,where sodium emits, the measured value can be considered tobe representative of the SL (or SCL) continuum. It is estimatedthat the contribution of Na emission to the PMT signal is lessthan 10%.During the pulse on-time, some active bubble population is

reached. In the subsequent pulse off-time, T0, bubbles undergodissolution. Some can also coalesce and hence modify thebubble size distribution, but this effect is neglected here as inprevious studies.3−5 Depending on their size at the end of aprevious acoustic pulse, some bubbles remain as nuclei for thesubsequent on-pulse. At very short off-times, all bubbles do notdissolve below a critical size and act as nuclei for thesubsequent on-pulse. When T0 is increased, some bubblesdissolve below a critical size range, and hence the SL (or SCL)intensity starts to decrease. Figure 1 shows typical SL vs off-

time data observed for a 0.5 M NaCl solution in the absenceand presence of luminol. Further details on this will beprovided in the Results and Discussion sections. A secondinflection point is seen in the curve, around 700 ms, andcorresponds to the dissolution of the maximum number ofactive cavitation bubbles below a critical size range. Therefore,as stated in a previous report,3 each increment in T0 above theonset of decreasing SL intensity corresponds to the dissolutionof bubbles with a given size.The bubble size and its distribution can be calculated from

the evolution of the SL intensity with T0. The equationdeveloped by Epstein and Plesset8 for a single dissolvingstationary bubble was used:

ρ

ρ

γ= +

⎛⎝⎜⎜

⎞⎠⎟⎟

⎛⎝⎜⎜

⎞⎠⎟⎟

DCR

tRT R

M13 2

1s

g 02

g 0

D is the diffusion coefficient of the gas.9 Since no experimentalvalues are available for the diffusion coefficients of Ar and He inNaCl solutions of a large concentration range, the dependenceof D on NaCl concentration was calculated considering that thediffusion coefficient follows a Stokes−Einstein relation andtherefore is inversely proportional to the liquid viscosity.Viscosity values at 25 °C were taken from the literature.10 Thediffusion coefficients obtained by this method are in satisfactoryagreement with the ones computed in a previous study.11

Cs is the dissolved gas concentration.12 Cs as a function ofNaCl concentration was calculated according to the model ofSchumpe.13 It is expressed in kg/m3 by using liquid densities ρLby Rogers and Pitzer.14 ρg is the gas density in the bubble,calculated by considering an average height below the water

Figure 1. Typical SL and SCL intensities vs pulse off-time curve; 0.5M NaCl solution (a) and 0.1 mM luminol solution (b), both under Arbubbling.

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level of 0.045 m. R0 is the initial bubble radius beforedissolution, corresponding to the ambient radius, i.e., the radiusof the bubble when it experiences a zero acoustic pressure; t isthe total dissolution time (here, T0); M is the molecular weightof the gas; R is the universal gas constant; T is the temperatureof the liquid, and γ is the surface tension.15 The increase insurface tension with NaCl concentration was taken to be 2.10(mN m−1)/(mol L−1).15 The values of the parameters used aresummarized in Table 1.

3. RESULTS3.1. Time Evolution of the SL Intensity during the

Pulse On-Time. Figure 2 shows the time evolution of SLintensity during the pulse on-time. It can be noticed that itsshape highly depends on the off-time and on the NaClconcentration. At long off-times, a steady-state population ofbubbles is usually not reached within the pulse on-time; on thecontrary, short off-times (before the sharp drop in SL occurs)usually lead to a steady-state population of active bubbles. Thelatter does not hold for high NaCl concentrations: at 5 MNaCl, for instance, in both Ar and He, the PMT signal increasesuntil the end of the US pulse, indicating that no steady-statepopulation of bubbles has been reached within the pulse on-time.Due to technical limitations, off-times lower than 4.2−4.3 ms

could not be set. For this reason, the maximum in the SLintensity increase was not reached for NaCl concentrations of3−5 M in He and 5 M in Ar. For these experimentalconditions, the larger size part of the bubble size distributionwas therefore not determined.3.2. Bubble Size Distributions. The bubble size

distributions are summarized in Figure 3a,b for Ar and inFigure 4a,b for He, for SL bubbles in water for all NaClconcentrations from 0 to 5 M, and for sonochemically activebubbles in 0.1 mM luminol with NaCl concentrations in therange of 0−3 M. It is to be noted that the measurement in 5 MNaCl in luminol under Ar did not lead to any intense lightemission in the pulsed mode, suggesting that either the on-timewas not sufficient to reach a population of active bubbles or thatthe bubble size corresponded to a T0 too small to be set, whichwould correspond to a size smaller than 0.25 μm. It is also

possible that the presence of a high concentration of chlorideions influenced the reaction between OH radicals and luminol.The size of the SL bubbles ranges from 0.2 to 4.7 μm under

Ar flow and from 0.3 to 3.9 μm under He flow for NaClconcentrations of 0 to 5 M. The size of SL and SCL bubblesdecreases when NaCl is present. In all cases the bubble size isbelow the linear resonance size of 8.5 μm as calculated in waterby the Minnaert equation,16 in good agreement with previousmeasurements and theoretical work.17 This difference wasexplained by the strong nonlinearity of bubble collapse.Besides, in general the size distributions become narrower

with the addition of NaCl. In some cases, the distributionappears to be bimodal. The spread in the distribution of thebubble sizes is reflected in the rate at which the SL intensitydecreases as a function of pulse off-time as depicted in Figure 1,showing a typical PMT intensity vs pulse off-time for a broaddistribution (0.5 M NaCl, Ar) and for a narrow size distribution(luminol, Ar). The time interval over which the intensity dropsis about 500 ms in the first case and 40 ms in the second.

4. DISCUSSION4.1. SL Bubbles vs SCL Bubbles. As observed in air-

saturated water sonicated at 575 kHz,5 the mean bubble size isalways lower for SCL bubbles than for SL bubbles, independentof the nature of the dissolved gas (Ar, He) and the saltconcentration. This was explained on the basis of therequirement for higher bubble core temperatures needed forSL,5 in agreement with the observation that SCL bubblesappear at lower acoustic power levels than do SL bubbles.18 It isnoteworthy that a smaller size is predicted for sonochemicallyactive bubbles than for SL bubbles.17b It might be argued,however, that the surface-active properties of luminol mayaffect the extent of coalescence. To ensure that this was not thecase at the low luminol concentration studied, SL spectra weremeasured in water and 0.1 mM luminol under Ar (Figure 1SI inSupporting Information): the intensity of the SL continuum isbarely changed by the addition of luminol, confirming that thebubble size and number are hardly affected.

4.2. Effect of NaCl Addition. An increase in NaClconcentration leads to a clear decrease in bubble radius. Thismay be due to the coalescence inhibiting effect of NaCl:19 by

Table 1. Parameters Used to Determine the Bubble Size Corresponding to a Given Dissolution Time for Ar and He

[NaCl], mol/L 0 0.5 1 2 3 4 5

Ar

D, m2/s 1.23 × 10−9 1.08 × 10−9 1.06 × 10−9 1.02 × 10−9 0.99 × 10−9 0.96 × 10−9 0.94 × 10−9

Cs, kg/m3 0.0589 0.0516 0.0451 0.0344 0.0262 0.0198 0.0150

ρL, kg/m3 998 1019 1038 1074 1108 1139 1169ρg, kg/m3 1.669 1.669 1.669 1.669 1.670 1.670 1.670M, kg/kmol 39.948 39.948 39.948 39.948 39.948 39.948 39.948R, J/kmol·K 8314 8314 8314 8314 8314 8314 8314T, K 293 293 293 293 293 293 293γ, N/m 0.072 0.07305 0.0741 0.0762 0.0783 0.0804 0.0825

He

D, m2/s 6.76 × 10−9 5.92 × 10−9 5.81 × 10−9 5.61 × 10−9 5.44 × 10−9 5.30 × 10−9 5.16 × 10−9

Cs, kg/m3 0.00150 0.00140 0.00130 0.00112 0.00097 0.00083 0.00071

ρL, kg/m3 998 1019 1038 1074 1108 1139 1169ρg, kg/m3 0.167 0.167 0.167 0.167 0.167 0.167 0.167M, kg/kmol 4.0026 4.0026 4.0026 4.0026 4.0026 4.0026 4.0026R, J/kmol.K 8314 8314 8314 8314 8314 8314 8314T, K 293 293 293 293 293 293 293γ, N/m 0.072 0.07305 0.0741 0.0762 0.0783 0.0804 0.0825

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decreasing the dissolved gas concentration, the electrolytereduces the number of microbubbles that would promotebubble coalescence,15 hence inhibiting bubble growth. Indeed,it has been shown that decreasing the dissolved air content by50% leads to a broader spatial distribution of SL bubbles.20 Thisis caused by a smaller number of degassed bubbles (formed bycoalescence) that would otherwise cause an attenuation of thesound wave. By decreasing this attenuation, a stronger standingwave is established.4.3. Effect of the Gas Type. He SL bubbles are smaller

than Ar SL bubbles up to a salt concentration of 2 M, they haverelatively the same size as Ar SL bubbles at 3 and 4 M, and theyare slightly larger at 5 M (Figure 5). This changing trend maybe attributed to the coupling of the effects of the main twoparameters affecting bubble growth by gas diffusion: the gassolubility and its diffusion coefficient. The gas solubility ishigher for Ar, leading to larger Ar bubbles at low saltconcentration. As for the role of the gas diffusion coefficient,

it can be exemplified by considering in Figure 6 the one gassolubility value (3.8 × 10−4 mol/kg) that is common to Ar andHe. At this value, He bubbles are much larger, which may beexplained by He having a much larger diffusion coefficient (6.76× 10−9 m2·s−1 in water) compared to that of Ar (1.23 × 10−9

m2·s−1 in water) that would allow bubbles to grow larger ineach expansion phase.Similarly, the size of SCL bubbles decreases upon addition of

salt, and while the Ar bubble is larger in water, Ar and He SCLbubbles have approximately the same size at 1 M NaCl.

4.4. Effect of Continuous Gas Bubbling. The observeddecrease in the bubble size when salt is added is in agreementwith a previous study4 of the influence of NaCl concentrationon the SL bubble size. The latter study was performed at a USfrequency of 515 kHz with the same reactor geometry, aftersaturation of the solution with Ar or He but without continuousbubbling. Bubble sizes measured in both previous and currentstudies are summarized in Figure 5, after corrections of the

Figure 2. Evolution of the normalized SL intensity during pulse on-time for water and NaCl solutions, under Ar or He continuous bubbling, for off-times shorter (red curves) and longer (black curves) than the off-times corresponding to the sharp drop in SL. The second curve was y-shifted forclarity. The SL signal is given as negative values that correspond to the output signal of the photomultiplier tube.

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values presented in the previous study4 for the dependence ofgas diffusion coefficients on NaCl concentration.The bubble sizes obtained in water in both studies are in fair

agreement. Though larger bubbles would be expected at lowerfrequency, the expected difference is small (Figure 1 in ref 5).Besides, the powers used (0.17 W/mL here vs 0.1 W/mL in thestudy4 at 515 kHz) lie in the power interval where the size isapproximately constant5 and should therefore not lead to anysignificant difference in bubble size.Though similar sizes are obtained in water in both studies,

interestingly they follow different trends upon addition of salt.First, smaller bubble sizes are obtained in the present study,although somewhat larger bubbles would be expected at thelower frequency. This discrepancy cannot be explained by thefact that at the higher frequency (515 kHz) more oscillationstake place per unit time so that a shorter on-time would benecessary to reach the steady-state population. Indeed, it can beobserved in Figure 2 that for NaCl concentrations below 3 Mand for both gases steady-state populations are achieved here.Second, the most important difference between both sets ofcurves is their shapes. This difference is made even clearerwhen the bubble size is plotted against the gas solubility (Figure6): while the bubble size decreases almost linearly at 515 kHzin an Ar (respectively He)-saturated solution, an inflectionpoint is observed in the present study with a faster decrease inthe bubble size between 0 and 2 M NaCl. At higher NaClconcentration both curves are approximately parallel.Observed differences can be traced back to the effect of

continuous bubbling of the gas into the solution in the presentstudy, while in the previous one4 the solution was “only”

saturated with the gas of interest before the measurements.This should not induce any big change in the dissolved gasconcentration due to the short experiment duration and theshort on-time compared to off-times. On the other hand, as gasis bubbled continuously, more nuclei are present in the solutionand therefore more bubbles can form that have to share thesame amount of dissolved gas to grow. Hence the smallerbubble sizes reached under continuous bubbling. The higherthe NaCl concentration the lower the amount of dissolved gas

Figure 3. Bubble size distribution as a function of the NaClconcentration in water (a) and in 0.1 mM luminol solutions (b),under Ar bubbling. The uncertainty is estimated to be about 0.1 μm.

Figure 4. Bubble size distribution as a function of NaCl concentrationin water (a) and in 0.1 mM luminol solutions (b), under He bubbling.The uncertainty is estimated to be about 0.1 μm.

Figure 5. Evolution of the average SL (respectively SCL) bubble sizewith NaCl concentration, under Ar and He, at 355 kHz undercontinuous gas bubbling (present data) and at 515 kHz after saturationof the solution with the chosen gas.4

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and bubbles can only grow to a small size. This corresponds tothe first part of the curves in Figure 6, for NaCl concentrationshigher than 2 M: for each gas both curves are parallel since thebubbles grow by diffusion from the same amount of gas. Below2 M NaCl, the dissolved gas concentration is higher and somecoalescence can take place and form SL bubbles. Continuousbubbling will enhance the coalescence by introducing morenuclei. This larger amount of coalescence under continuous gasbubbling is in good agreement with the observed broader sizedistributions observed here for SL bubbles in water and in 0.5M NaCl solution under Ar. For the same solutions, the bubblesize distributions are narrower under He due to a reduction ingas solubility and the number of gas nuclei, which results in alower degree of coalescence, leading to a narrower sizedistribution under He. Hence, not only the gas solubility andits diffusion coefficient but also the number of bubble nucleiappears to govern the bubble size. This interpretation issupported by the recently reported21 bubble sizes in aqueous 3M NaCl sonicated at 90 kHz under Ar flow; these bubble sizeswere measured with a high-speed camera and correspond to allpresent bubbles, not only to sonoluminescence and sonochemi-cally active bubbles. It was observed that at a very low Ar flowrate (7 mL/min) the most probable size was larger than athigher (46 or 92 mL/min) flow rates, and this was traced backto the formation of many nuclei under Ar flow rates by thefragmentation of large bubbles.As shown in Figure 6, the gas solubility significantly differs

for the different gases, and data can be more easily comparedafter normalization of the bubble radius and the gas solubility totheir values in water, as shown in Figure 7.After normalization treatment, our data show distinctly

separate curves for Ar and He as opposed to that reported byBrotchie et al. (in the absence of continuous flow) where bothAr and He collapse into one curve. Our data indicates that inthe 0−2 M NaCl concentration range the rate of increase in thebubble size with increasing gas solubility is faster in the case ofHe compared to Ar. This is attributed to the much higher Hediffusion coefficient. In the absence of continuous bubbling thisdifference is hardly observed because the solution around thebubbles is rapidly depleted in dissolved He due to the very lowsolubility of He.

5. CONCLUSIONSLooking at the bubble size distribution as a function of NaClconcentration under a continuous bubbling of He or Ar, thisstudy brought to light that the dissolved gas concentration,controlled by the salt concentration, is not the only parameterthat governs coalescence and the bubble size but that otherparameters also play an important role. In particular, thepresence of continuous bubbling, which is characteristic ofmany real sonochemical systems, appears to decrease thebubble size by introducing more bubble nuclei. Besides, the gasdiffusion coefficient also appears to be a major parameter in thedefinition of the bubble size: when the gas solubility is highenough, a high gas diffusion coefficient leads to the formationof larger bubbles due to faster growth in each expansion cycle.This study thus opens perspectives on new parameters thatwould affect the sonochemical activity. Indeed, while a smallerbubble size should a priori lead to lower sonochemical activityper bubble, the effect of continuous gas bubbling maycounterbalance this effect by the introduction of more bubblenuclei and a subsequently higher number of active bubbles. Theextent of each effect will depend on the nature and solubility ofa gas and on the nature of the solution (if a solute is present ornot).

■ ASSOCIATED CONTENT*S Supporting InformationThe Supporting Information is available free of charge on theACS Publications website at DOI: 10.1021/acs.jpcb.5b08723.

Sonoluminescence spectra of water and luminol 0.1 mMmeasured under a continuous Ar flow at 359 kHz, Pac =35 W, 13 °C using the setup described in previouswork.22 The comparison of the SL continuum intensityof these two spectra indicates that bubble size andnumber are barely affected by the addition of luminol.(PDF)

■ AUTHOR INFORMATIONCorresponding Author*E-mail: rachel.pflieger@cea.fr. Tel: +33 466339250.NotesThe authors declare no competing financial interest.

Figure 6. SL bubble size as a function of gas solubility. Figure 7. Bubble radius normalized for Ar and He with respect to theradius measured in pure water as a function of the normalizeddissolved gas concentration.

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■ ACKNOWLEDGMENTS

We thank Jean-Francois Dufreche and Bertrand Siboulet(ICSM) for fruitful discussions and for technical help in thefitting of the curves.

■ REFERENCES(1) Mason, T. J.; Peters, D. Practical Sonochemistry Power UltrasoundUses and Applications, 2nd ed.; Woodhead Publishing: 2002.(2) Iida, Y.; Ashokkumar, M.; Tuziuti, T.; Kozuka, T.; Yasui, K.;Towata, A.; Lee, J. Bubble Population Phenomena in SonochernicalReactor: I Estimation of Bubble Size Distribution and its NumberDensity with Pulsed Sonication - Laser Diffraction Method. Ultrason.Sonochem. 2010, 17 (2), 473−479.(3) Lee, J.; Ashokkumar, M.; Kentish, S.; Grieser, F. Determination ofthe Size Distribution of Sonoluminescence Bubbles in a PulsedAcoustic Field. J. Am. Chem. Soc. 2005, 127 (48), 16810−16811.(4) Brotchie, A.; Statham, T.; Zhou, M. F.; Dharmarathne, L.;Grieser, F.; Ashokkumar, M. Acoustic Bubble Sizes, Coalescence, andSonochemical Activity in Aqueous Electrolyte Solutions Saturated withDifferent Gases. Langmuir 2010, 26 (15), 12690−12695.(5) Brotchie, A.; Grieser, F.; Ashokkumar, M. Effect of Power andFrequency on Bubble-Size Distributions in Acoustic Cavitation. Phys.Rev. Lett. 2009, 102 (8), 084302.(6) Brotchie, A.; Grieser, F.; Ashokkumar, M. Characterization ofAcoustic Cavitation Bubbles in Different Sound Fields. J. Phys. Chem. B2010, 114 (34), 11010−11016.(7) (a) Ashokkumar, M.; Hall, R.; Mulvaney, P.; Grieser, F.Sonoluminescence from Aqueous Alcohol and Surfactant Solutions.J. Phys. Chem. B 1997, 101 (50), 10845−10850. (b) Tronson, R.;Ashokkumar, M.; Grieser, F. Comparison of the Effects of Water-Soluble Solutes on Multibubble Sonoluminescence Generated inAqueous Solutions by 20- and 515-kHz Pulsed Ultrasound. J. Phys.Chem. B 2002, 106 (42), 11064−11068.(8) Epstein, P. S.; Plesset, M. S. On the Stability of Gas Bubbles inLiquid-Gas Solutions. J. Chem. Phys. 1950, 18 (11), 1505−1509.(9) (a) Maharajh, D. M.; Walkley, J. Temperature-Dependence ofDiffusion-Coefficients of Ar, CO2, CH4, CH3Cl, CH3Br, AndCHCl2F in Water. Can. J. Chem. 1973, 51 (6), 944−952. (b) Jahne,B.; Heinz, G.; Dietrich, W. Measurement of the Diffusion-Coefficientsof Sparingly Soluble Gases in Water. J. Geophys. Res. 1987, 92 (C10),10767−10776.(10) Zhang, H. L.; Han, S. J. Viscosity and Density of Water plusSodium Chloride plus Potassium Chloride Solutions at 298.15 K. J.Chem. Eng. Data 1996, 41 (3), 516−520.(11) Ivlev, D. V.; Kiselev, M. G. Helium Diffusion in AqueousSodium Chloride Solution at High Pressures. Russ. J. Phys. Chem. A2012, 86 (6), 974−978.(12) http://www.engineeringtoolbox.com/gases-solubility-water-d_1148.html, e. t. Solubility of Gases in Water. (accessed 14/11/2013).(13) Schumpe, A. The Estimation of Gas Solubilities in Salt-Solutions. Chem. Eng. Sci. 1993, 48 (1), 153−158.(14) Rogers, P. S. Z.; Pitzer, K. S. Volumetric Properties of AqueousSodium-Chloride Solutions. J. Phys. Chem. Ref. Data 1982, 11 (1), 15−81.(15) Weissenborn, P. K.; Pugh, R. J. Surface Tension of AqueousSolutions of Electrolytes: Relationship with Ion Hydration, OxygenSolubility, and Bubble Coalescence. J. Colloid Interface Sci. 1996, 184(2), 550−563.(16) Leighton, T. G. The Acoustic Bubble; Academic Press: London,1994.(17) (a) Merouani, S.; Hamdaoui, O.; Rezgui, Y.; Guemini, M.Effects of Ultrasound Frequency and Acoustic Amplitude on the Sizeof Sonochemically Active Bubbles - Theoretical Study. Ultrason.Sonochem. 2013, 20 (3), 815−819. (b) Yasui, K.; Tuziuti, T.; Lee, J.;Kozuka, T.; Towata, A.; Iida, Y. The Range of Ambient Radius for anActive Bubble in Sonoluminescence and Sonochemical Reactions. J.Chem. Phys. 2008, 128 (18), 184705.

(18) Ashokkumar, M.; Lee, J.; Iida, Y.; Yasui, K.; Kozuka, T.; Tuziuti,T.; Towata, A. Spatial Distribution of Acoustic Cavitation Bubbles atDifferent Ultrasound Frequencies. ChemPhysChem 2010, 11 (8),1680−1684.(19) Browne, C.; Tabor, R. F.; Chan, D. Y. C.; Dagastine, R. R.;Ashokkumar, M.; Grieser, F. Bubble Coalescence during AcousticCavitation in Aqueous Electrolyte Solutions. Langmuir 2011, 27 (19),12025−12032.(20) Lee, J.; Yasui, K.; Tuziuti, T.; Kozuka, T.; Towata, A.; Iida, Y.Spatial Distribution Enhancement of Sonoluminescence Activity byAltering Sonication and Solution Conditions. J. Phys. Chem. B 2008,112 (48), 15333−15341.(21) Cairos, C.; Schneider, J.; Pflieger, R.; Mettin, R. Effects of ArgonSparging Rate, Ultrasonic Power, and Frequency on MultibubbleSonoluminescence Spectra and Bubble Dynamics in NaCl AqueousSolutions. Ultrason. Sonochem. 2014, 21 (6), 2044−2051.(22) Pflieger, R.; Ndiaye, A. A.; Chave, T.; Nikitenko, S. I. Influenceof Ultrasonic Frequency on Swan Band Sonoluminescence andSonochemical Activity in Aqueous tert-Butyl Alcohol Solutions. J.Phys. Chem. B 2015, 119 (1), 284−290.

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