Fresh water is a scarce source. Demand for freshwater is greater than supply, due to the increasing industrialisation of countries and the low natural supply of freshwater sources such as rivers and lakes. Contamination of these natural freshwater sources by industrial wastewater adds to the freshwater deficit. Throughout history, technologies have been developed to increase the supply of fresh water by desalinating other water sources into fresh water. Reverse osmosis is the most widely used desalination technology for seawater desalination, but the energy transition calls for electric-based technologies that can desalinate water using renewable energy sources. Capacitive deionisation is a relatively new desalination technology that uses electrical energy to desalinate brackish water. The capacitive deionisation cell is an electrochemical cell in which the feed water flows between two electrodes. When electricity is applied to these electrodes, ions in the water are attracted to move towards the porous electrodes where they are adsorbed within the electrical double layer. Unfortunately, the capacitive deionisation system has some challenges: it is a batch-system, has a low freshwater production and it has not been built for large-scale production. Avsalt AB, a Swedish company, has developed a new capacitive deionisation architecture to address these challenges, called the multichannel capacitive deionisation system (MC-CDI). This system consists of two capacitive porous electrodes and several membrane-like electrodes between them, referred to as capacitive membrane electrodes (CMEs). To maximise the performance of the multichannel deionisation system, the performance of the capacitive membrane electrodes should be enhanced. Therefore, the aim of his thesis is to optimise the physical properties of the capacitive membrane electrodes that affect the performance of the capacitive membrane electrodes and to gain a better understanding of how the microscopic properties of the CMEs should be carefully tailored to improve the performance. To address these questions we can turn to Electrochemical Impedance Spectroscopy (EIS). EIS is a non-invasive measurement technique that may be regarded as a much more sophisticated resistance measurement compared to, for example, a multimeter. In contrast to the latter device, EIS measures the impedance, which is a combination of the resistance and the reactance, at a wide range of frequencies. The frequency dependency of the measured impedance can be used to find a so-called equivalent electrical circuit model (EECM). For EIS measurements on electrochemical cells, such as batteries, fuel cells, and electrolysers, the EECM elucidates the different electrochemical processes that occur at different timescales and impedance plots are used to analyse and compare these electrochemical processes. EIS has been successfully used to analyse the electrochemical processes within CDI electrodes and ion exchange membranes, but capacitive membrane electrodes used in an MC-CDI system have never been studied with an accurate and fast measurement technique such as EIS. Because CMEs do not have a solid support structure, in contrast to most CDI electrodes, ions are free to migrate through the electrodes. Therefore, the alternating current that is needed in EIS measurements can be applied on an external set of electrodes, while the response alternating voltage can be picked up at the CMEs. This 4-point impedance measurement configuration enables precise determination of the ionic resistance and capacitance of the electrode material. Therefore, an electrochemical impedance spectroscopy setup is built to determine the performance indicators of the CMEs and to gain a better understanding of the electrochemical processes taking place at the interface of the CMEs. The resulting Nyquist and Bode plots are used to analyse the ion diffusion and capacitive behaviour of the electrodes. To enable the analysis, first, an equivalent electrical circuit is determined for these freestanding electrodes. It was found that the CME can be represented by the Transmission-line model, which in the equivalent electrical circuit takes the form of a junction of three complex impedances. From the values of the electrochemical parameters, the performance indicators of the CME, membrane conductivity and permselectivity, were evaluated. The CME meter presents itself as an accurate measurement system to quickly evaluate the performance indicators of the CME, with the aim of efficiently searching for the CME that will show the best performance within the MC-CDI system, without placing it within the MC-CDI system. Further research should be conducted to investigate the extent to which EIS could be used to estimate the permselectivity of the CME and whether the total measurement time to predict permselectivity is still short enough to propose EIS as an alternative measurement technique.

Non-photochemical laser-induced nucleation (NPLIN) is a crystallisation method in which a highly structured phase is formed out of solution by exposure to a laser beam. NPLIN offers unprecedented spatiotemporal control and characterisation of nucleation. NPLIN is energy efficient compared to conventional crystallisation methods and can be implemented in continuous microfluidic reactors, enabling sustainable operation. However, its working principles are not yet fully understood. This study contains an evaluation of four proposed mechanisms and a description of an experimental setup involving an ultrahigh speed camera. Two mechanisms describe interaction of molecular polarisation with the electric field, either isotropically known as dielectric polarisation (DP), or anisotropically via the optical Kerr effect (OKE). The other two mechanisms involve cavitation bubble formation by nanoparticle heating through light absorption. This work contains a refined description of this so-called cavity-induced nucleation where its consequences are distinguished into two mechanisms, either based on concentration enhancement (CICEN) or due to pressure enhancement (CIPEN). Novel theoretical calculations in conjunction with experimental data suggest that NPLIN phenomena are based on DP or CICEN, potentially operating in concert. It is conjectured that the influence of DP and CICEN can be quantified further by development of a topological description of DP, simulations of CICEN and relating nucleation probabilities to the metastable zone width of various solutes. The calculations suggest that OKE and CIPEN have little significance because involved energies are several orders of magnitude below kBT . The proposed setup allows for observing the NPLIN phenomena and establishing dependence on cavitation bubbles, providing empirical validation. Solutions to experimental problems are provided, including reduction of sample fluid evaporation, aligning the nucleation site with the region of interest of the camera and removing image noise.

Counterfeiting of food and pharmaceutical products, albeit a more serious issue in developing countries is, however, omnipresent. Therefore, there is an ever-growing need for anticounterfeiting measures to address this challenge. Currently, the existing overt and covert anticounterfeiting measures are more prevalent on the packaging of such products. While such measures are helpful to a certain extent, they are however, easier to by-pass with re-used authentic packaging, fake barcodes and duplicate product numbering. Furthermore, advanced research and new innovations have indicated that it is also possible to have additional levels of security by incorporating similar measures into or on the product itself. Although these novel anticounterfeiting measures offer a unique opportunity to safeguard the customer’s interest at best, they present certain challenges. Some of these include bio-compatibility of the materials and the need for them to be in compliance with regulatory organizations. However, overcoming these challenges confronts the issue directly. In this work, the approach is to develop a proof of concept of entirely edible barcodes from naturally available and/or food grade materials such as sodium alginate. This study also focusses on the influence of drying on the macroscopic structure of such barcodes. The bar-codes are produced by physically cross-linking the polymer in specific moulds, converting them into a hydrogel barcode in itself. Altogether, this work provides a qualitative under-standing that such a concept can be developed and that the significant structural changes upon drying is not exclusively governed by the concentration of sodium alginate.

This report aimed to investigate jet-breakup through nozzles and its dependencies on viscosity, flowrate and nozzle diameter. By measuring the transition point from dripping to jetting as a function of nozzle diameter and viscosity, it was found that increasing nozzle diameters require increasing flowrates to reach jetting mode, while increasing viscosity lowers the critical flow-rate for the transition point. The breakup length was also observed to be influenced by both viscosity, flow-rate and nozzle size: increasing either viscosity or flow-rate resulted in an increase of the breakup length. Matching these results in dimensionless form to predictions in literature proved to be difficult, presumably due to the relatively small nozzle diameters used in this research.

The recent advancements in lab-on-a-chip technologies has led to numerous studies on the collective dynamics of micro-particles suspended in a microfluidic channel. The role of hydrodynamics in “self-steering” of the particles in a low Reynolds flows is explicitly dependent only on the particle’s exterior geometry. Thus richer responses can be achieved by controlling the transport and orientation of asymmetric particles under external flow. In this work, we study the universal behaviour of particles with any arbitrary shape, strongly confined along direction involving height. The particle both translates and rotates in-plane, until a stable orientation is reached, after which it drifts cross-stream. By combining analytical, numerical and experimental techniques, we establish the generalised equations of motion for a particle sufficiently far away from the channel walls along width. Thus, the total motion of a particle is characterized by estimating only a few timescales, intrinsic to its exterior geometry. We discuss the shape properties defining the dynamics, and use them to derive an analytical framework. The results are then validated against the numerical solution utilizing an improved 2-Dimnesional Brinkman formulation for highly confined particles. Experiments are performed using stop-flow lithography, where the dynamics of the photo-polymerized particles are observed by driving it out of equilibrium using an externally imposed pressure difference. We confirm the universal behaviour of the particles, except for a few cases, only when close to the stable orientation. Our experimentally observed rotational timescales consistently match the numerically computed values when multiplied by a factor of 1.8.

While colloidal suspensions of non-spherical particles have been studied relatively extensively, granular suspensions of non-spherical particles are rarely studied. The rheological behaviour of elongated granular particles is therefore not well known. This thesis deals with suspensions of rod-like particles of aspect ratio 4 subjected to shear flow in a low-density, highly viscous Newtonian fluid. CFD-DEM simulations for a periodic shear box have been performed for a pre-estimated range of shear rates and volume fractions. Dependence of rheological properties like shear stresses, relative viscosity, granular temperature, pressure and normal stress differences on the shear rate and volume fraction have been studied. These granular rods show shear thickening behaviour. The spherocylindrical particle suspensions experience less collisional stresses than spherical particles due to preferred particle alignment in the shear direction. Herschel and Bulkley [1] model is used to fit the collisional stress data. Two different regimes have been identified for granular suspension based on the flow index. Interestingly, a relatively large range of shear rates and associated stress can be expressed in the form of a simple equation based on Broughton and Squires [2] model. This stress closure will further be used in more coarse grid models like MP-PIC which can simulate an industrial fluidized bed reactors of non-spherical particles.

Colloidal allostery is a regulatory mechanism where specific metabolites regulate the protein activity by binding to them and changing their energy landscape. The first steps to model this system on a colloidal scale were made by studying the depletion interaction between the hydrogel posts and the rigid polystyrene particles. Using soft lithography, hydrogel posts of different rigidity were synthesized inside the microfluidic channel. Polystyrene particles and depletant (dextran) were added and the interaction between the posts and the particles was studied using optical microscopy and particle tracking. However, major issues such as poor statistics, incomplete cross-linking of the hydrogel posts and irreversible sticking of polystyrene particles to the hydrogel hindered with the experimental results. Therefore, in this project, efforts are made to improve the experimental implementation of the model. At the end of the project, it was observed that while optical tweezers offer a more controlled and refined way of measuring the interactive forces than the particle tracking using video microscopy, the limitations of the equipment in providing the location of the particle normal to the base of the channel hinder the estimation of the desired parameter. Furthermore, despite curing the hydrogel posts for a long period of time under the UV light, the rigid polystyrene particles still stick irreversibly to the post. It is therefore recommended that the optical tweezer apparatus must be upgraded to provide the researcher with the position of particle normal to channel bottom. This can allow better estimation of the effect of the wall on the motion of the particle. The photo-crosslinking characteristics of the hydrogel must be studied to determine the effect of the UV light on the gelation process. The ultimate vision of the project is to develop innovative separation technologies based on the fundamental understanding of the interplay of the depletion forces and elastic energy of deformation. of the hydrogel posts.

Crystallization is one of the most sought after separation and purification technique in the process industries. However, the fundamental understanding on the formation of crystals poses quite a challenge due to the inherent complexity and stochasticity associated with the process. In the past, several attempts put forth to control crystal nucleation have been anything but successful. But, more recently, the use of lasers to control primary nucleation have led to promising prospects. In the current study, efforts were made to explore the phenomena behind Non-Photochemical Laser Induced Nucleation (NPLIN). Experiments were carried out starting with a confined microfluidic system for both supersaturated aqueous potassium permanganate and potassium chloride solutions and later extended to unconfined geometry with potassium chloride solutions. A single nanosecond laser pulse of 532 nm wavelength was employed to create vapour bubbles and the resulting crystal formation was quantified. To begin with, a quadratic relationship between the laser energy supplied and the maximum radius of the bubble formed was observed. By systematically varying both the supplied laser energy and the solution supersaturation, the probability of crystal formation for various energy–supersaturation combinations were studied. A minimum laser energy threshold for crystal formation was observed to be a function of solution supersaturation. The results obtained in this study will aid in developing a numerical model that can apriori predict the minimum necessary laser and supersaturation conditions required for any given salt to undergo NPLIN.

Kidney stones may be uncommon is certain parts of the world. On the other hand, considering the percentage of cases in the western world, one can say it is worrisome. Anyone can have kidney stones, which may be easily passed out of the kidney through the urine. It only becomes a cause for concern when the stones grow beyond a certain size. They can cause flank and abdominal pains, fever, painful urination, etc., and can subsequently result in kidney failure if the patient has only one kidney present. In that case, a kidney stone patient may require the attention of a nephrologist. Advancement in technology has provided conventional techniques such as ureteroscopy (URS), percutaneous nephrolithotomy (PNL) and shockwave lithotripsy (SWL) for treating kidney stones. One may wonder what exactly these stones are. They are nothing extraordinary but rather made of calcium oxalate (CaOx) crystals which are formed from a supersaturated urine. CaOx crystal which is a product of crystallization occurs in two forms, calcium oxalate monohydrate (COM) and calcium oxalate dihydrate (COD). Crystallization is a very simple and effective purification and phase separation process used in the chemical and pharmaceutical industry. This process is usually influenced by many factors such as concentration, temperature, mixing, impurities, etc. The presence of oxalate in urine is a major contributor to the formation of kidney stones. High concentration of oxalate combines with calcium to form CaOx. On the other hand, injury to the kidney tubular epithelial cells results in the expression of Hyaluronic acid (HA). HA has since been considered as a binding agent which causes the retention of kidney stones. Furthermore, some scientists are of the idea that HA may also influence the formation of kidney stones. A novel method was developed to study the nucleation kinetics of CaOx in artificial urine under the influence of varying oxalate and HA concentrations. The method involved crystallizing CaOx (COM, COD) in emulsions (micro-droplets) that were generated by and stored in a microfluidic device. Incorporating polarized lightmicroscopy also allowed COM and COD to be detected at the same time. The cumulative probability distribution as a function of induction time for COM and COD was determined and fitted to the Weibull model. The induction time is the average time at which the first crystal is detected in the droplets. As was expected, higher oxalate concentration shortened the induction time for both COM and COD. Surprisingly, increasing HA concentration induced the formation of COM whiles inhibiting the formation of COD. In general, the frequency of COD was always less than that of COM. In conclusion, the idea that HA played a role in the formation of kidney stones was confirmed. This was the most important part of the research.

The dwindling of natural resources, mainly fossil fuels, and the alarming increase in the global average temperatures, are the biggest concerns of the engineering and scientific community of 21st century. Studies have found that known reserves of oil and natural gas will last another 50 years. Coal will last another 110 years, which points towards dire consequences. The experience will not be that of a car slowly running out of gas, but rather like driving off a cliff, since we innately depend on these resources. The realization of these concerns has lead to a rise in the investments all over the globe for Sustainability. The right questions are now being asked. How can we fulfill our demands without compromising the demands of our future generations? One of the keen areas of interest is the conversion of power into fuel. Synthesis of hydrocarbons from sequestrated carbon can produce carbon-neutral fuels that can replace some of the conventional fossil fuels. Methanol has been actively wiping the floor with the research community due to its simplicity of production and less toxic nature. While there are quite a lot of ways of producing methanol, very few of them are carbon neutral. Zero Emission Fuels B.V. has embarked on a venture to produce methanol by a totally carbon neutral process. They begin by capturing carbon dioxide and water from air and splitting the water into hydrogen and oxygen using solar power. Carbon dioxide and hydrogen are then combined in a reactor to form methanol, making a truly carbon-neutral process. They aim to make fuel consumption, a completely circular process while keeping it economic. An experimental characterization of ZEF’s methanol reactor under varying pressures and H2/CO2compositions was done. The new reactor design focuses on heating the feed gases before catalyst bed, more heat integration, reliable sensor data, and the ability to mix gases in desired compositions. Methanol yield, quality, energy efficiency, reactor inlet and outlet temperatures, power requirements were experimentally determined in a transient analysis. It was seen that the reactor produces 4.84 mmol/gcat /hr of methanol at 50 Bar and reactor wall temperature of 250◦C with H2 : CO2 = 3:1 mol% feed gas. The catalyst exhibited partial deactivation during night after shutdown. Contrary to expectation, the reactor produced more methanol at lower pressure. The production was reported at 5.96 mmol/gcat /hr at 35 Bar. Although, only 4.36 mmol/gcat /hr at 25 Bar. Moreover, the pressure reduction caused the natural circulation to slow down, and increase the inlet temperature from 208◦C at 50 Bar to 234◦C at 35 Bar, which is the reason for the observed increase in yield. It can be concluded that the reactor yield under these conditions is limited by kinetics and not thermodynamics. The reduced mass flow rate allowed the reactor to consume less power and show higher energy efficiency. It increased from 34.7% at 50 Bar to 43.2% at 35 Bar. The rate of pressure decline in the reactor was correlated with the methanol yield using gas law by accounting for non-ideality with the compressibility factor. The predicted yield was seen to be in good agreement with experimentally determined. The methanol yield of the reactor with variable feed gas composition was obtained for 50 Bar and 250◦C reactor wall temperature and seen to decrease on either side of the ideal composition. It was concluded that the yield becomes both stoichiometrically and kinetically limited. It is recommended that similar experiments be done at increasing temperatures and equilibrium yield be determined experimentally. Additionally, the reactor needs to be operated with varying compositions and higher reactor wall temperatures at constant pressure, to obtain the operating line for maximum production of reactor.

To tackle the expected increase in fresh water shortage in the world, alternative water production methods are required. One such a possible method is Ocean Thermal Water Production (OTWP). This thesis continues on the innovative concept of the use of OTEC waste water as a cooling fluid for atmospheric water production introduced in previous work. In this thesis, an experimental study on a structured packed bed condenser column is presented. This work was carried out on an experimental OTWP set-up installed in the Process & Energy lab at the Delft University of Technology. Additionally, a numerical Python model was used to investigate the heat transfer and condensation characteristics of the packed bed column. The condenser function of the Python model was used to compare the prediction performances of different mass transfer coefficient and hydraulic correlations. The Python model simulations were compared both to the predictions of Aspen plus, an established chemical process software, and to the experimental results. The correlation by Olujic et al. (1999) was chosen as the most suitable for the transfer rate and hydraulic behavior predictions for the Python condenser model. A mean average error in the mass transfer predictions of 2.5 % and in the hydraulic predictions of 16.9% was reached in relation to the experiments. outperforms the Aspen plus model, that has respective mean average errors for the mass and pressure drop predictions of 9.5% and 13.0 % for the correlation proposed by Rocha et al. (1993). The Python model was extended with functions that calculate the pressure drop over the remaining necessary equipment for an OTWP plant. The aim of the developed model was to predict the processes in the OTWP condenser column and design a pilot-plant. The model was used to perform a sensitivity analysis on a large-scale column. A preliminary economic analysis identified that reducing the diameter of the condenser column reduces the cost of water production but increases the energy requirement. For an OTWP pilot-plant with a production of 25 m3/day, the chosen column diameter of 6.6 m leads to a system energy requirement of 3.5 kWh/m3 and a levelized cost of water production of 8.08 $/m3. Those production costs can be reduced by an optimization study of the full OTWP pilot-plant.

Supercritical water gasification is a process in which wet biomass is converted to bio-syngas. In this process the temperature and pressure are raised above the critical point of water (374 C, 221 bar), creating a supercritical medium in which a high conversion and energetic efficiency of biomass to bio-syngas is realized. Due to these high efficiencies supercritical water gasification has received much attention as a potential treatment technique for sewage sludge from wastewater treatment plants. To design a supercritical water gasification process kinetic models are used. They provide predictions on the decomposition products of the organic components of the biomass during treatment. However, kinetic data on lipids, which can make up to 25% of the organic matter in sewage sludge, are not available yet. This study aims to identify main reaction pathways and corresponding kinetic parameters that describe the decomposition of lipids in supercritical water. Experiments were performed to provide data of decomposition products yields and find the dominant reaction pathways. Oleic acid was used as a model compound for lipids from sewage sludge. Experiments were conducted in a stainless steel batch reactor which was heated by immersion in a fluidized hot sand bath. Investigated temperatures and residence times were 400, 420, 460 and 520 C and 15, 35 and 65 min, respectively. Oleic acid feed concentration was 10 wt% and a pressure of 25 MPa was applied. From experimental results the decomposition of oleic acid into aliphatic hydrocarbons and shorter chain fatty acids was identified. With increasing time and temperature these products would either gasify or the aliphatic hydrocarbons would dehydrogenate to cyclic and (poly)-aromatic compounds. A remarkably high selectivity towards the light hydrocarbon gases (C2H6, C2H4, C3H8, C3H6) compared to an earlier study into the decomposition of oleic acid in supercritical water was observed for all temperatures and residence times. Parameters for a kinetic model, build up from the identified reaction paths, were fitted to the experimental data using Matlab. The Arrhenius equation was used to describe the reaction constants as function of temperature. For the oleic acid decomposition an activation energy of 151 kJ/mol was fitted first with a percentage output variation of 82% between 420 C and 520 C. Parameters for the other reactions were fitted using this activation energy as constraint. Qualitative trends on the gas and liquid decomposition products distribution over time and temperature were predicted well by the model, but predictions on the quantitative yield of them were concluded to be inaccurate. Largest differences between experimental and model yields were observed for CH4 and the light hydrocarbon gases. One reason for these model errors is the scarcity of data points in the 0-15 min time-scale, where the process was highest in reactivity. Also some of the reaction pathways in the model might have been oversimplified, neglecting certain dominant decomposition reactions.

The structuring of polymers on the micro and nanoscale is performed largely by lithographic techniques, which require complex steps and suffer from geometrical and scaling limits. Techniques such as Nanoimprint Lithography and Hot Embossing are attractive alternatives as they can produce high quality nanoscale structures with a high throughput. Colloidal building blocks offer a way to self-assemble the masters required for these replication steps. However, the difficulty with self-assembly lies in the creation of stable structures with little defect that are well controlled. This work sets out to provide a comprehensive overview of the aspects of the fabrication of colloidal crystals, the most influential parameters and how they can be qualified. Offering a basis for future research on microscale replication by colloidal crystals and resulting in development of a method for the fabrication of colloidal crystal, which can be used as a master to replicate microscale patterns through Hot Embossing.

This thesis describes a study into pairwise particle interactions within a Hele-Shaw geometry, using stop-flow lithography. By exposing a photoreactive mixture to a strong UV-pulse, a hydrogel is formed. The shape of this hydrogel is controlled by masking part of the light beam. This process takes place while the Hele-Shaw channel is placed on the stage of a microscope, which allows these hydrogel particles to be viewed and tracked. Improvements were made to increase the accuracy and precision of the experimental set-up. No- tably, the initially present mismatch of intra-pair particle thickness was greatly reduced by changing the method of particle pair production. By tracking these pairs of particles, information is obtained regarding their motions and velocity relative to one another. Experiments were performed for a selection of particle shapes and compared to numerical simulations of identical geometries. Simulations predicted that attractive and repulsive velocities should be noticed depending on the separation distance and shape of the particles. Qualitatively, the experiments agree to a certain extent with the simulations. It was demonstrated that the pairwise interactions are indeed dependent on their shape. Furthermore, the magnitude of these interactions qualitatively matched with the experimental data. Quantitatively, the experimental data did not agree with the simulations, but strong evidence was presented to indicate that the UV-light hitting the sample was not uniformly distributed. This results in a discrepancy in particle thickness between the pair, which skews the experimental data. Novel insights were gained on the applicability of the current literature model on hydrogel particle propagation. In contrast to the current model, it was experimentally demonstrated that the shape and (in-plane) size of the particle affects its thickness.

Kidney stone formation is a global health problem with increasing prevalence. Stone formation is a physiochemical process involving crystallization of inorganic salts in the presence of biological constituents in the urinary system. To inhibit kidney stone formation, a better understanding of the underlying physicochemical mechanism of stone formation in the kidney is required. In this thesis, the solubility, nucleation and growth of calcium oxalate (CaOx), the most common inorganic constituent of kidney stones, were studied under different conditions such as ion concentration, pH value, and also the role of inhibitors in water or artificial urine was investigated. The first step towards this work was obtaining the solubility curve of calcium oxalate monohydrate (COM) in the solvent, such as ultrapure water and different buffers, to elucidate the physicochemical conditions which can cause the kidney stone formation (Chapter 2). Beside the solubility study, advanced technology to observe crystal formation in small scale and a very short time was needed. The volume, structure and flow properties inside the kidney inspired us to use microfluidic technology with comparable volume and flow rate. The developed microfluidic devices that mimic pathways in the human kidney were used to study the nucleation and growth of calcium oxalate crystals. The developed devices rendered an alternate perspective to the study of kidney stone formation and showed that microfluidics can provide precise, simple and fast detection of stone formation under various experimental conditions. Initially, the designed microfluidic device allowed us to build a testing platform for the study of nucleation kinetics of CaOx inside isolated environments provided by droplets. Preliminary experiments were performed by dissolving calcium chloride and sodium oxalate in ultrapure water. The aqueous solution, containing the ions, forms the droplet phase and oil were used as the continuous phase. Altering the pH values, as well as increasing the concentration of additives such as magnesium and osteopontin (OPN), were shown to slow down the nucleation kinetics, or even inhibit nucleation (Chapter 3). @en

Nephrolithiasis is a disease of the urinary tract system, caused by accumulating waste products which form small stones. It is known to affect people all over the world, with a prevalence in populations as high as 16.7 % in North East Thailand and 18.5 % in uranium workers in Eastern Tennessee, USA. The most found stones are Calcium (𝐶𝑎)Oxalate (𝑂𝑥)based crystals, which form when their concentrations are supersaturated in the kidney, thus exceeding their solubility limit. The most common forms of CaOxcrystals in urine are the stable Calcium Oxalate Monohydrate (COM) and the metastable Calcium Oxalate Dihydrate (COD). If they grow too large and get stuck, medical surgery is necessary to prevent kidney failure. It is therefore necessary to understand this form of biomineralization within the human body to ensure proper treatment and prevention. This study focuses on mimicking the situation in the collecting duct of the kidney. This is done in a 295𝑥45 𝜇𝑚T-shaped microchannel, wherin a 𝐶𝑎solution enters through one inlet and an 𝑂𝑥solution through a second, such that the combined fluid flowing through the main channel is supersaturated. 𝐶𝑎 and 𝑂𝑥 are dissolved in either water or artificial urine based on the works of Streit et al. In this manner, the following effects are studied: the effect of varying average velocity, the effect of adding an amount of the natural inhibitor Osteopontin in the 𝑂𝑥-inlet, and the effect of changing the 𝐶𝑎 to 𝑂𝑥 ratio in urine conditions. Besides the microfluidic experiments, three models are applied to understand the ongoing phenomena: the Surface Reaction Model (SRM)as an analytical model of the transport-reaction kinetics at the crystal surface, the Analytical Microchannel Model (AMM) as an analytical model of the momentum and mass transport through the microchannel, and the COMSOL model as a numerical model of the microchannel made in the Matlab program COMSOL. With the latter momentum and mass transport through the channel are calculated and the mass transport results are combined with Jess Urine Expert to calculate supersaturation profiles at the channel bottom, where the crystals grow. The number for the transport reaction kinetics of the crystal surface points out that the surface reaction limits the growth, not the mass transport. LowDamköhler numbers for the transport-reaction kinetics in the entire microchannel also point this out.