Title: Drop formation in multi-phase microfluidic flows
Description: In this thesis, we present a basic study on the formation of liquid jets and their subsequent break-up into drops in multi-phase coaxial flows. We utilize the jet breakup and drop formation mechanisms to generate monodisperse double emulsions, which we use to form novel spherically layered materials. In Chapter 1 we describe the basic dripping-to-jetting transition of a liquid injected into a second co-flowing immiscible liquid. We show that despite the large parameter space, the transition is controlled by the outer capillary number and the inner Weber number. In Chapter 2, using the same co-flowing geometry, we show with experimental evidence and a linear stability analysis that the jets generated with the inner Weber number break-up due to an absolute instability. In Chapter 3 we fabricate a micro-capillary device that combines the co-flowing geometry with a flow-focusing geometry to generate monodisperse double emulsions. We demonstrate the potential of this technique by generating novel core-shell structures. In Chapter 4 we describe an alternate method to generate highly controlled monodisperse double and triple emulsions using multiple co-flowing streams arranged in series. We again demonstrate that this device can be used to form multi-layered core-shell structures. In Chapters 6-8 we use the micro-capillary device from Chapter 3 to generate novel spherically layered materials from double emulsions. In Chapter 6 we describe the formation of diblock copolymer vesicles from double emulsions. During the formation of these polymer vesicles, the 'oil' phase can undergo an instability where it dewets from the diblock copolymer; this instability is described in Chapter 7. Finally, in Chapter 8 we generate and characterize temperature sensitive microgel spheres and a novel core-shell microgel structure.