Microbubbles formation

The overheating effect is believed to play a dominant role in explaining the physical mechanism of the microbubble formation, and three main reasons could be underpinned First, it was observed that a small amount of the glycerin injected into the gap would eventually disappear after a few hours at the positive EEF intensity of 1 MV/cm. Second, no remarkable difference in the chemical composition between the glycerin before and after the EEF was applied could be found in the experiment, which indicated physical effects might predominate. Besides, a rough estimation of the temperature rise in the contact region due to the electro-thermal effect will be conducted as follows. 

Li et al. [76] confirmed that efficacy of phenol degradation depends on microbubble formation. In their experiments, they observed no change in phenol concentration if micro-bubble formation was stopped. The phenol decomposition rate was found maximum in the case when O2 was passed in the solution due to highest micro-bubble formation followed by air and N2 respectively. 

SIZE DISTRIBUTION OF SYNTHETIC MICROBUBBLES FORMATION, COALESCENCE, FISSION, AND DISAPPEARANCE... 

Apparent reversible and/or cyclical behavior Microbubble formation and coalescence versus microbubble fission and disappearance... 

In conclusion, it is possible to prepare concentrated gas-inwater emulsions using various surfactant mixtures. The artificial, surfactant-stabilized microbubbles produced apparently undergo a cyclical process of microbubble formation/coalescence/fission/dis-appearance, where the end of each cycle is characterized by a collapse of the gas microbubbles into large micellar structures — only to re-emerge soon after as newly formed, gas microbubbles. This cyclical microbubble process is promoted by prior mechanical agitation of, and hence entrapment of macroscopic gas bubbles in, these saturated surfactant solutions. 

The microchannel emulsion technique has been extended to the formation of multiple emulsions [158-163], encapsulation [123, 158, 164—166], polymer bead formation [123, 125, 167-169], demulsification [116, 158, 170], and even microbubble formation [171]. New methods of stabilizing emulsions have also been investigated in this realm, including particle-stabilized [172] and protein-stabilized emulsions [173], with some work in emulsification without surfactants [135,146]. In the case of multiple emulsions, microchannel architecture can enable the formation of W/O/W emulsions in which two water droplets of different compositions can be encased in the same oil droplet [163]. 

K. (2004) Monodispersed microbubble formation using microchaimel technique. AIChE J., 50 (12), Sin- S133. 

M.W. Weber, R. Shandas, Computational fluid dynamics analysis of microbubble formation in microfluidic flow-focusing devices, Micrcfluidics Nanojluidics, 2007, 3, 195-206. 

The use of ultrasonic (US) radiation (typical range 20 to 850 kHz) to accelerate Diels-Alder reactions is undergoing continuous expansion. There is a parallelism between the ultrasonic and high pressure-assisted reactions. Ultrasonic radiations induce cavitation, that is, the formation and the collapse of microbubbles inside the liquid phase which is accompanied by the local generation of high temperature and high pressure [29]. Snyder and coworkers [30] published the first ultrasound-assisted Diels-Alder reactions that involved the cycloadditions of o-quinone 37 with appropriate dienes 38 to synthesize abietanoid diterpenes A-C (Scheme 4.7) isolated from the traditional Chinese medicine, Dan Shen, prepared from the roots of Salvia miltiorrhiza Bunge. 

It is possible that microbubble shell may be shattered during the interaction with an ultrasound pulse. Indeed, drastic variation of microbubble size, up to several-fold in less than a microsecond, has been reported [33], with linear speeds of the wall motion of microbubble approaching hundreds of meters per second in certain conditions. At these rates, it is easy to shatter the materials that would otherwise flow under slow deformation conditions. In some cases (e.g., lipid monolayer shells, which are held together solely by the hydrophobic interaction of the adjacent molecules), after such shattering the re-formation of the shell maybe possible in other cases - e.g., with a solid crosslinked polymer or a denatured protein shells - the detached iceberg-like pieces of the microbubble shell coat would probably not re-form and anneal, and the acoustic response of microbubbles to the subsequent ultrasound pulses would be different [34]. 

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