Sunartio Devi, Ashokkumar Muthupandian, Grieser Franz
Particulate Fluids Processing Centre, School of Chemistry, University of Melbourne, Melbourne, Victoria 3010, Australia.
J Am Chem Soc. 2007 May 9;129(18):6031-6. doi: 10.1021/ja068980w. Epub 2007 Apr 18.
The effect that surface-active solutes, such as aliphatic alcohols and sodium dodecyl sulfate (SDS), have on the extent of bubble coalescence in liquids under different sonication conditions has been investigated by measuring the volume change of the solution following a period of sonication. In general, the adsorption of surface-active solutes onto the bubble surface retards bubble coalescence. Within the limitations of the measurement method and the systems studied, bubble coalescence does not appear to be dependent on the applied acoustic power. Also, varying the applied acoustic frequency has a minimal effect on the extent of bubble coalescence in systems where long-range electrostatic repulsion between bubbles, imparted by the adsorbed surface-active solutes, dominates. However, when short-range steric repulsion (or other short-range repulsive forces) is the primary factor in inhibiting bubble coalescence, the dependence on the applied acoustic frequency becomes apparent, with less coalescence inhibition at higher frequencies. It is also concluded that SDS does not reach an equilibrium adsorption level at the bubble/solution interface under the sonication conditions used. On the basis of this conclusion, a method is proposed for estimating nonequilibrium surface excess values for solutes that do not fully equilibrate with the bubble/solution interface during sonication. For the case of SDS in the presence of excess NaCl, the method was further employed to estimate the maximum lifetime of bubbles in a multibubble field. It was concluded that an acoustic bubble in a multibubble field has a finite lifetime, and that this lifetime decreases with increasing applied frequency, ranging from up to 0.35 +/- 0.05 ms for 213 kHz to 0.10 +/- 0.05 ms for 1062 kHz. These estimated lifetimes equate to a bubble in a multibubble field undergoing an upper limit of 50-200 oscillations over its lifetime for applied ultrasound frequencies between 200 kHz and 1 MHz.
通过测量超声处理一段时间后溶液的体积变化，研究了脂肪醇和十二烷基硫酸钠（SDS）等表面活性溶质在不同超声处理条件下对液体中气泡聚并程度的影响。一般来说，表面活性溶质在气泡表面的吸附会阻碍气泡聚并。在所研究的测量方法和体系的限制范围内，气泡聚并似乎不依赖于所施加的声功率。此外，在由吸附的表面活性溶质赋予气泡之间长程静电排斥起主导作用的体系中，改变所施加的声频对气泡聚并程度的影响极小。然而，当短程空间排斥（或其他短程排斥力）是抑制气泡聚并的主要因素时，对所施加声频的依赖性就变得明显，在较高频率下聚并抑制作用较小。还得出结论，在所使用的超声处理条件下，SDS在气泡/溶液界面未达到平衡吸附水平。基于这一结论，提出了一种估算在超声处理过程中未与气泡/溶液界面完全达到平衡的溶质的非平衡表面过量值的方法。对于存在过量氯化钠时的SDS情况，该方法进一步用于估算多气泡场中气泡的最大寿命。得出的结论是，多气泡场中的声泡具有有限的寿命，并且该寿命随着所施加频率的增加而减小，对于213 kHz，寿命范围可达0.35±0.05 ms，对于1062 kHz，寿命为0.10±0.05 ms。这些估算的寿命相当于在200 kHz至1 MHz的超声频率下，多气泡场中的气泡在其寿命期间经历50 - 200次振荡的上限。
