Microbubbling of viscous liquids and suspensions.
Doctoral thesis, UCL (University College London).
This research comprises of device designing and processing of biomaterial suspensions based on co-flowing medium and air. The preparation of stable microbubble suspensions is fundamental to a wide range of technological applications across the scientific, engineering, medical and industrial sectors; from the production of basic foodstuffs to the self-assembly of smart materials. A key requirement in such preparation is to control the size distribution (i.e. mean and standard deviation) of the resulting microbubbles, with ideally a monodispersion being achieved. Such quality control is important because when the microbubbles are used in, for example, in ultrasound imaging, the response of such a microbubble to ultrasound excitation is strongly influenced by the radius and the thickness of the microbubble and also the mechanical properties of any coating material. This response, in tum, determines the amplitude and frequency of the ultrasound signal scattered by the microbubbles and the threshold for microbubble destruction. In first part of the work, a device is designed and optimized to microbubble silicone oils of different viscosities. All the important physical parameters like liquid and air flow rate, capillary diameter, gap between two capillaries, viscosity and surface tension are investigated to understand the mechanisms of bubble formation and to idealise the processing technique. The condition of bubble formation; a ratio of air to liquid pressure is found to be related to viscosity of liquid which is important in materials processing. Bubble dynamics are also modelled to predict the air jet diameter which can control the diameter of bubble being produced. It was shown that air jet diameter has a strong relationship to viscosity of the liquid. Secondly, using a similar device and technique, lipid suspension and nano gold particulate colloids are microbubbled to show that process is suitable for producing near monodisperse microbubbles with more than 20 minutes life time. These microbubbles have immediate application as ultrasound contrast agent and drug delivery vehicle. Moreover, it is also found that nano-particulate reinforced bubbles can enhance the non-linearity of backscatter at low amplitude pressure. To further reduce the diameter of bubbles, a hybrid flow focussing and electrospraying device is developed to show that monodisperse size of bubbles less than 10 μm can be produced. This process has been syslematically studied to conclude that the product of applied voltage and flow ratio governs the diameter of bubbles generated.
|Title:||Microbubbling of viscous liquids and suspensions|
|Additional information:||Authorisation for digitisation not received|
|UCL classification:||UCL > School of BEAMS > Faculty of Engineering Science > Mechanical Engineering|
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