Active Droplet Control and Manipulation in Microfluidics

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Nguyen, Nam-Trung

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Tan, Say Hwa H

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Droplet microfluidics involves the use of small volumes of fluids dispersed in an immiscible phase to perform multiple functions. Droplet microfluidics brings advantages such as the miniaturization of experiments, portability of devices, efficient use of resources and capabilities for scaling up production. These tools have been finding their use in a broad range of applications, from chemical and biological analysis to optics and information technology. Various types of controls have been developed to enable the manipulation of droplets. These techniques are categorized into passive and active methods. Passive methods only involve the device geometries and the fluid flow. Active techniques on the other hand provide another level of controllability for adjusting droplet parameters, allowing rapid change of droplet parameters within a single experiment. This flexibility enables user to select parameters and subsequent actions on the same device. Particularly, droplet-on-demand systems benefit from these techniques. The aim of this thesis is the development of different active methods for droplet manipulation. The thesis first focuses on three active control methods, pneumatic, acoustic and electric. Firstly, negative pressure is applied for the controlling droplet generation in a device. The novel application of negative pressure directly affects the flow in the microchannel to generate droplets on demand. This control approach, unlike other active approaches eliminates space constraints within the device with no need for external equipment. Next, a new fabrication approach for interdigitated transducers for generating acoustic waves was developed. This approach eliminates the use of expensive fabrication equipment and simplifies fabrication procedures. Acoustic streaming in a droplet was successfully demonstrated with these transducers. Finally, electric methods are used for controls in droplet generation and coalescence. Non-Newtonian droplets are generated through application of the electric field. On-demand coalescence of droplets is also observed using a combination of AC electric field and a micropillar. The new approaches reported in this thesis provide a greater versatility in microfluidics applications. The simpler alternatives suggested here would overcome current limitations of fabrication complexity and large device footprint, allowing microfluidics to be more accessible and easily implemented. The outcome of this thesis contributes to enhancing the uptake of microfluidics in multidisciplinary research and to broadening the user base of this technology.

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Thesis (PhD Doctorate)

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Doctor of Philosophy (PhD)


School of Eng & Built Env

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Droplet microfluidics

droplet manipulation


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