Droplet microfluidics generates and manipulates microdroplets in microfluidic devices at high manufacturing efficiency and controllability. Microdroplets have proven effective in biomedical applications such as single-cell analysis, DNA sequencing, protein partitioning and drug delivery. Conventionally, a series of aqueous microdroplets containing biosamples is generated and controlled in an oil environment. One of the critical challenges in this system is that recovery of the aqueous samples from the oil phase is very difficult and often requires expensive and cumbersome post-processing. Also, the low Reynolds (Re) number characteristic of this system results in low throughput of droplet generation. To circumvent challenges and fully utilize microdroplets for practical clinical applications, this research aims to unpack the fundamental physics that governs droplet generation in oil-free systems including an aqueous two-phase system (ATPS) and a high inertial liquid-gas system. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2019. / FAU Electronic Theses and Dissertations Collection