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Date of Conference: 4-9 October 2020 Conference Name: 24th International Conference on Miniaturized Systems for Chemistry and Life Sciences, MicroTAS 2020 The ability to measure physical properties of droplets in real-time is required to design precise operations on droplet-based systems. In this study, we implemented a real-time droplet tracker that tracks the positions of droplets and measures droplet generation frequency as well as droplets' physical properties, such as size, size distribution, shape, velocity, circularity. Furthermore, using the droplet length, we use curve fitting to determine the dispersed phase viscosity. Our droplet tracker is implemented in Python, using the OpenCV library and can be run on a routine PC.

Cataloged from PDF version of article. Thesis (Ph.D.): Bilkent University, Department of Materials Science and Nanotechnology, İhsan Doğramacı Bilkent University, 2020. Includes bibliographical references (leaves 93-103) Droplet fluidic systems have dramatically improved precision in many applications, such as polymerase chain reaction, biochemical analysis, and particle synthesis in which accurate control of sample volume plays a significant role. Despite the well-understood physics of squeezing regime droplet formation in two-phase flow systems, the long-sought-after goal of generating identical, equal size droplets is challenging. Although the individual parameters that affect the droplet size were identified as channel dimension, wettability, viscosity, and flow rate or pressure ratio of the two immiscible fluids, the governing mechanism of droplet size variation is not completely analyzed. More importantly, the limit of monodispersity for droplet generation systems is still unknown. This is due to the difficulty in analytical modeling of droplet formation that is usually compensated by experimental approaches, which fall short in leading to universal conclusions. In this thesis, depending on the flow source used for driving fluids we present an analytical approach that takes into account all the system dynamics and internal and external factors that disturb monodispersity. We use the analogy between fluidic and electrical circuits to analyze the factors that influence droplet monodispersity. Interestingly, we enable to model the dynamics of a segmented two-phase flow system using a single-phase flow analogy, electron flow, in electrical circuits. Doing so, we reveal the sources of disturbances that lead to variation in droplet volume. We offered a unique solution and designed guidelines to ensure ultramonodisperse droplet generation. Our analytical conclusions are experimentally verified using a T-junction and flow-focusing droplet generator design driven by a pressure supply. Equally importantly, we show the limiting experimental factors for reaching the theoretical maximum of monodispersity. For the displacement pump case, we propose a more effective and widely applicable solution to improve flow stability, by controlling off-chip compliances to minimize fluctuations due to the flow source. Eventually, we compare the performance of the two common drive units (pressure-driven and displacement pump) in terms of droplet monodispersity, while using our proposed methods and guidelines. Finally, we did study in reaction kinetics of poly dopamine and hydrogen peroxide and synthesize silica and polyethylene glycol (PEG) particles and supramolecular polymer capsules with high monodispersity using ultra-monodisperse droplets. by Ali Kalantarifard Ph.D.

Micrometer-scale monodisperse droplets are produced to generate nanowalled supramolecular microcapsules using microfluidics for high reproducibility and high-throughput manipulation, efficient material consumption, and control over hierarchical structure, shape, and size. In this study, an optimized microfluidic droplet generation technique and a unique liquid–liquid interfacial polymerization method were applied to fabricate the monodisperse polyrotaxane–based supramolecular microcapsules in a fast and simple way. To minimize the uncertainty due to droplet volume variation, the inlet pressures were supplied from the same source while lowering the interfacial tension and the main channel hydrodynamic resistance, which are critical for high monodispersity. The target polyrotaxane network (PN) was simply formed at the interface of the water and oil phases in ultra-monodisperse microdroplets via the cucurbit[6]uril (CB6)-catalyzed azide–alkyne cycloaddition (CB6-AAC) reaction between azido- and alkyne-functionalized tetraphenylporphyrin monomers (TPP-4AZ and TPP-4AL). The thickness of the interfacially assembled PN microcapsules was 20 nm as analyzed by cross-sectional TEM and TEM-EDX techniques. The resultant water-in-oil PN microcapsules were highly monodisperse in size and able to retain target molecules. Here, rhodamine 6G (Rh6G)-loaded PN microcapsules were fabricated, and the release rate of the Rh6G cargo was investigated over time for controlled drug release applications.

Droplet-based microfluidic systems require a precise control of droplet physical properties; hence, measuring the morphological properties of droplets is critical to obtain high sensitivity analysis. The ability to perform such measurements in real-time is another demand which has not been addressed yet. In this study, we used coplanar electrodes configured in the differential measurement mode for impedimetric measurement of size and velocity. To obtain the size of the droplets, detailed 3D finite element simulations of the system were performed. The interaction of the non-uniform electric field and the droplet was investigated. Electrode geometry optimization steps were described and design guideline rules were laid out. User-friendly software was developed for real-time observation of droplet length and velocity together with in situ statistical analysis results. A comparison between impedimetric and optical measurement tools is given. Finally, to illustrate the benefit of having real-time analysis, iDM was used to synthesize particles with a predefined monodispersity limit and to study the response times of syringe pump and pressure pump driven droplet generation devices. This analysis allows one to evaluate the 'warm-up' time for a droplet generator system, after which droplets reach the desired steady-state size required by the application of interest.