Surfactant Mediated Tipstreaming as a Tool for Designed Production of Sub-Micron Sized Droplets

Microscale tipstreaming is a hydrodynamic phenomenon capable of producing submicron sized droplets within a microfluidic device. Tipstreaming is the ejection of small drops from a liquid thread formed by interfacial tension gradients and convective transport of surfactant. To use tipstreaming in potential applications, including nanoparticle synthesis, chemical detection and separation, occlusion therapy, and others, it is necessary to understand and be able to control the thread formation process. However, there are many technical challenges restricting successful implementation of microscale tipstreaming. This thesis provides several tools and solutions to overcome these technical challenges. Modeling the tipstreaming phenomenon has allowed for prediction of conditions where tipstreaming is expected to occur for an arbitrary oil-watersurfactant system. This facilitates the use of tipstreaming to quickly estimate conditions where thread formation will be observed, reducing the need for experimentally determining the tipstreaming operating diagram. The key component of the model is the reliance on interfacial shape observations to simplify the fluid flow and surfactant transport equations. An active feedback control loop developed in this work is capable of eliminating the production of primary droplets and producing a continuous thread, and therefore a continuous droplet stream. Lastly, droplet size is characterized as a function of the surfactant concentration and liquid flow rates of the two phases leading to control over the size of the droplets being produced. Applying these tools to enhance tipstreaming is crucial in aiding its use in applications.