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Novel Preparation of Monodisperse Microbubbles by Integrating Oscillating Electric Fields with Microfluidics

1
Department of Mechanical Engineering, University College London, London WC1E 7JE, UK
2
Department of Physics and Astronomy, University College London, London WC1E 6BT, UK
*
Author to whom correspondence should be addressed.
Present address: Department of Mechanical Engineering, University of Birmingham, Birmingham B15 2TT, UK.
Micromachines 2018, 9(10), 497; https://doi.org/10.3390/mi9100497
Received: 28 June 2018 / Revised: 14 September 2018 / Accepted: 20 September 2018 / Published: 27 September 2018
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Abstract

Microbubbles generated by microfluidic techniques have gained substantial interest in various industries such as cosmetics, food engineering, and the biomedical field. The microfluidic T-junction provides exquisite control over processing parameters, however, it relies on pressure driven flows only; therefore, bubble size variation is limited especially for viscous solutions. A novel set-up to superimpose an alternating current (AC) oscillation onto a direct current (DC) field is invented in this work, capitalising on the possibility to excite bubble resonance phenomenon and properties, and introducing relevant parameters such as frequency, AC voltage, and waveform to further control bubble size. A capillary embedded T-junction microfluidic device fitted with a stainless-steel capillary was utilised for microbubble formation. Furthermore, a numerical model of the T-junction was developed by integrating the volume of fluid (VOF) method with the electric module; simulation results were attained for the formation of the microbubbles with a particular focus on the flow fields along the detachment of the emerging bubble. Two main types of experiments were conducted in this framework: the first was to test the effect of applied AC voltage magnitude and the second was to vary the applied frequency. Experimental results indicated that higher frequencies have a pronounced effect on the bubble diameter within the 100 Hz and 2.2 kHz range, whereas elevated AC voltages tend to promote bubble elongation and growth. Computational results suggest there is a uniform velocity field distribution along the bubble upon application of a superimposed field and that microbubble detachment is facilitated by the recirculation of the dispersed phase. Furthermore, an ideal range of parameters exists to tailor monodisperse bubble size for specific applications. View Full-Text
Keywords: microfluidics; superimposed electric fields; microbubbles; CFD microfluidics; superimposed electric fields; microbubbles; CFD
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Kothandaraman, A.; Harker, A.; Ventikos, Y.; Edirisinghe, M. Novel Preparation of Monodisperse Microbubbles by Integrating Oscillating Electric Fields with Microfluidics. Micromachines 2018, 9, 497.

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