Dynamic behavior and interactions of ferrofluid droplets under magnetic fields in low Reynolds number flows

Digital microfluidics in combination with emulsion microfluidics are crucial building blocks of droplet-based microfluidics, which are prevalent in a wide variety of industrial and biomedical applications, including polymer processing, food production, drug delivery, inkjet printing, and cell-based assays. Therefore, understanding the dynamics and interactions of droplets as well as the interactions between the droplets and solid surfaces are of great importance in order to improve the performance or product in these applications. Recently, several studies in the literature have demonstrated the potential of magnetic fields in controlling the behavior of droplets in microscale; however, the fundamental mechanism behind the interesting dynamics of droplets and the full potential has not been fully understood. To advance both fundamental knowledge as well as demonstrate practical applications, this research combines both numerical and experimental approaches to investigate novel manipulations of ferrofluid droplets using magnetic fields. The first part of this research focuses on the numerical and experimental investigations on deformation and lateral migration of microscale ferrofluid droplets in shear flows, while the second and third parts, utilizing a numerical approach, explore the breakup and interactions of droplets under uniform magnetic fields, respectively. Next, the fourth part demonstrates the potential of permanent magnetic fields in the control of coalescence of sessile droplets on hydrophobic surfaces, while the fifth part studies the freely falling droplets under the influence of gravity and a uniform magnetic field. Finally, both numerical and experimental approaches are adopted to investigate the wetting and bouncing dynamics of ferrofluid droplets upon impact onto a solid flat surface under permanent magnetic fields. The results demonstrate several simple, versatile and powerful methods for the manipulation of droplet dynamics using magnetic fields, which can play a crucial role in droplet-based applications”--Abstract, page iv