This thesis conducts numerical and experimental studies of the nonlinear electrokinetic motion of heterogeneous particles in microfluidic systems and their corresponding applications in laboratory-on-a-chip (LOC) systems. Induced-charge electrokinetic (ICEK) phenomena flow is generated by applying an external electric field to a conducting particle immersed in an aqueous solution. As a result of this field, micro-vortices form around the conducting particle. Using this phenomenon, many shortcomings of classical electrokinetics (e.g. poor mixing, leakage, back flow problem) can be improved. This thesis proposes and investigates a complete 3-D numerical multi-physics method to calculate the induced zeta potential on the conducting surface of a heterogeneous object. To model the ICEK motion of a heterogeneous particle in a DC electric field, the moving grid technique is used to conduct the particle-fluid simulation. It was numerically shown that the vortices form near the conducting surface of a particle. Both transitional and rotational motions of heterogeneous particles are investigated. A set of novel experiments are designed and conducted to investigate several aspecs of ICEK. It is demonstrated for the first time that four vortices form around a conducting sphere in contact with an aqueous solution while the DC electric field is applied. The motions of heterogeneous particles are experimentally studied. The speed of a heterogeneous particle is compared with the same size non-conducting particle under the same experimental conditions and it is shown that the heterogeneous particle moves significantly faster than the non-conducting particle. It is also shown that the micro-vortices on the conducting section of the heterogeneous particle act like an engine and push the particle to move faster. These experiments verify the results of our simulation studies. We introduce three applications for induced-charge electrokinetic phenomena in ths thesis: ICEK micro-valve, ICEK micro-mixer, and ICEK micro-motor, which can be used in microfluidics and lab-on-a-chip devises. This ICEK micro-valve significantly improves many shortcomings of other micro-valves reported in the literature (such as leakage, considerable dead volume and complicated fabrication processes). Our ICEK micro-mixers take the advantages of induced micro-vortices and boost the mixing process in a micro-channel. As a result well mixed homogeneous (100%) mixture could be obtained at the downstream of the mixer. Our proposed no-contact ICEK micro-motor rotates as long as the DC electric field is being applied. This thesis develops a new understanding of several ICEK phenomena and applications related to heterogeneous particles. The 3D numerical model developed in this thesis along with the experimental studies are capable of describing the ICEK motion of a heterogeneous particle and is a considerable step to calculate the ICEK phenomena for real-world applications. This thesis, for the first time, experimentally visualized and verified the induced micro-vortices around conducting particles under applied DC electric field. The proposed ICEK micro-mixers, valve and motor can be used in various LOC devices and applications.

Les propriétés électrocinétiques de cellules ou de complexes colloïde-cellule visant leur manipulation individuelle dans une puce microfluidique devrait permettre de proposer de nouveaux types d'application dans le domaine des laboratoires-sur-puce et de la recherche biomédicale. Les travaux présentés dans ce manuscrit visent à créer une nouvelle technologie de puce microfluidique permettant la manipulation électrocinétique tridimensionnelle sans contact de particules colloïdales. Cette technologie innovante associée à la réalisation de particules colloïdales multifonctionnelles (Janus) permet d'étudier et de contrôler les interactions d'un complexe colloïde-cellule. Une technologie originale de puce microfluidique tridimensionnelle transparente présentant des niveaux d'électrodes biplanaires est développée sans couche résiduelle classiquement présente dans les technologies de scellement microfluidique. Parallèlement, de nouveaux types de colloïdes anisotropes (Janus) et multifonctionnels (fluorescents, fonctionnalisés avec des protéines…) sont fabriqués en associant la synthèse colloïdale aux techniques de la microélectronique et à la fonctionnalisation de surface. La compréhension et l'exploitation des forces électrocinétiques créées par un champ électrique alternatif et non-uniforme sur la solution colloïdale confinée dans cette puce permettent de proposer une nouvelle méthode de détermination du facteur de Clausius-Mossotti. Ce facteur est un paramètre intrinsèque à la solution colloïdale qui régit la force diélectrophorétique. La détermination expérimentale de ce facteur, combinée à une analyse théorique pour les solutions colloïdales étudiées, définit les paramètres du champ électrique à appliquer (fréquence, tension) pour localiser, séparer ou manipuler en trois dimensions des particules micrométriques de tout type (particules nu, fonctionnalisées, disymétriques…). Le mélange de ces particules dans des milieux de culture cellulaire contenant des cellules de lignées humaines crée des complexes colloïde-cellule. En fonction du type cellulaire, ces complexes se caractérisent par une cellule ayant internalisé des colloïdes ou une cellule décoré par des colloïdes attachés sur sa membrane. Soumis à des forces électrocinétiques déterminées, ces complexes démontrent des réponses duales des particules et des cellules contrôlables indépendamment. En combinant l'ingénierie des particules colloïdales et la technologie microfluidique de manipulation électrocinétique sans contact, des forces locales peuvent être exercées sur les cellules par l'intermédiaire des particules. / The electrokinetics properties of cells or a particles-cell complex for their individual handling in a microfluidic chip open the way to new applications for lab-on-chip or biomedical research fields. The work presented in this thesis aims to create a new technology of microfluidic chips able to perform 3D electrokinetic contactless handling of colloidal particles. Combined with the microfabrication of multifunctional (Janus) colloidal particles this technological breakthrough allows the study and the control of colloidal particles and cells. An innovative technology of a 3D transparent microfluidic chip that integrates two levels of bi-planar electrodes is developed without any residual layer commonly stacked in microfluidic sealing technology. At the same time, a new type of anisotropic particles (Janus) and multifunctional (fluorescence, functionalized with proteins) are microfabricated by combining colloidal synthesis, microelectronics process and surface functionalization techniques. The understanding and the use of electrokinetic forces that are created by a non-uniform electric field in a colloidal solution confined in this chip enable the access to a new method of determination of the Claussius-Mossotti factor. It is an intrinsic parameter of a colloidal solution that rules the dielectrophoretic force. Its experimental determination, combined with a theoretical analysis of the colloidal solution, defines the parameters of the electric field to apply (frequency, applied voltage) in order to localize, separate or handle in 3D all types of micrometer sized particles (plain, functionalized, dissymmetric). The mixing of particles in cell culture mediums that contain human lines cells creates a particle-cell complex. According to the cellular type, those complexes are characterized by a cell that has internalized particles or is decorated by particles attached on its membrane. Submitted to determined electrokinetic forces, those complexes show dual responses that are controllable on both particles or cell independently. By associating the engineering of colloidal particles and this electrokinetic contactless handling microfluidic technology, local forces can be exerted on cells via those particles.

Malgré un rôle important en physique, biologie et dans les processus industriels tels l’agroalimentaire et la dépollution de l’eau, la dynamique d'une particule colloïdale à proximité d'une interface fluide et ses interactions avec l’interface sont des phénomènes physiques encore débattus.Dans cette thèse, nous explorons la dynamique et l'interaction de particules colloïdales individuelles à proximité d'une interface air-eau à l’équilibre thermique.Afin de mener cette étude sans perturber le système expérimental, nous avons conçu et construit un microscope interférentiel à double onde adapté à l'interface air-eau. Contrairement à d'autres techniques expérimentales, notre configuration permet la mesure précise de la distance absolue entre particule l'interface sans nécessiter d’étalonnage ou d’hypothèse sur l'emplacement de l'interface. Nous avons ainsi pu obtenir des trajectoires hautement résolues de particules en 3D proches de l'interface, permettant la mesure précise des diffusions proche de l’interface et des interactions particules-interface.Le système montre deux profils d’énergie potentielle différents. Deux distances d’équilibre particule-interface sont ainsi observées. La plus grande peut être expliquée par la compétition des interactions de Van der Waals et électrostatiques avec la pesanteur. La distance d’équilibre plus courte ne peut s’expliquer que par la présence d’une interaction attractive supplémentaire. Les origines possibles de cette interaction sont discutées.En utilisant une nouvelle méthode d'analyse des déplacements quadratiques moyens des particules dans un potentiel générique, nous avons pu accéder aux coefficients de friction visqueuse des particules en fonction de la distance à l'interface. De manière singulière, l’interface air-eau se comporte comme une paroi liquide pour le mouvement des particules parallèlement à l’interface et comme une paroi solide pour le mouvement des particules perpendiculaire à l’interface. Ce résultat expérimental peut être partiellement rationalisé en considérant des modèles récents basés sur l’incompressibilité de surface. Cependant, certaines différences entre les expériences et les théories demeurent. Les coefficients de friction visqueuse sont plus importants que les prédictions hydrodynamiques et dépendent de la charge électrique des particules, ce qui suggère un possible rôle des phénomènes électrocinétiques.Enfin, le piégeage des particules à l'interface air-eau et leur angle de contact ont été mesurés tout en modifiant la force ionique de la solution aqueuse et en faisant varier l‘état de surface des colloïdes. / Despite the relevance to environmental, biological and industrial processes, the motion of a colloidal particle close to a fluid interface and the way it interacts with the water surface are still largely elusive and intriguing physical phenomena.In this thesis, we explore the motion dynamics and the interaction of individual colloidal particles close to an air-water interface in thermal equilibrium.In order to investigate them without perturbing or altering the experimental system, we designed and built a dual-wave reflection interference microscope working with an air-water interface geometry. Contrary to other established experimental techniques, our set-up allows accurate measurements of the absolute particle-interface distance and thus does not require any calibration or assumption to know the location of the interface. Highly resolved 3D particle trajectories close to the interface were obtained, from which information on particle diffusion close to the interface and particle-interface interactions are obtained.The system shows two different potential energy landscapes resulting in two different equilibrium particle-interface distances. The larger one can be fairly explained by Van der Waals and electrostatic interactions combined with gravity. The shorter one highlights the existence of an unexpected additional attractive interaction. The possible origins of such an interaction are discussed.Using a method of analysis of the particle mean square displacements in a generic potential we developed, we were able to access to particle drag coefficients as a function of the distance from the interface. Peculiarly, the air-water interface acts as a slip boundary for the particle motion parallel to the interface and as a no-slip boundary for the particle motion perpendicular to the interface. This experimental result can be partially rationalized considering recent models based on surface incompressibility. However, some discrepancies between experiments and theories remain. Experimental drag coefficients are larger than the hydrodynamic predictions and depend on the particle electrical charge, pointing therefore to a possible role of electrokinetic phenomena.Finally, the particle trapping at the air-water interface and its contact angle were observed while tuning the ionic strength of the aqueous solution and varying the surface state of the colloids.

A literature survey on modelling of the resistance spot welding process has been carried out and some of the more interesting models on this subject have been reviewed in this work. The underlying physics has been studied and a brief explanation of Heat transfer, electrokinetics and metallurgy in a resistance spot welding context have been presented.\nl\hsLastly a state of the art model and a simplified model, with implementation in the FEM software LS-DYNA in mind, have been presented.

The objective of this research was to evaluate the technical and economic feasibility of employing an electric field to enhance the dewatering performance of two types of biological sludge by a pilot-scale plate and frame filter press. In this work a biological industrial sludge and biological municipal sludge were collected and tested, respectively. Through the jar testing, it was found that a low molecular weight cationic polymer or medium molecular weight cationic polymer with a dose of 0.008 wt% would yield a satisfactory flocculation for the biological industrial sludge, whereas an iron-based coagulant with a dose of 0.08 wt% would meet the conditioning need of the biological municipal sludge. To find out the optimal dewatering conditions for the concerned sludges, experimental designs based on the Taguchi method were adopted. More specifically, L8(27) and L18(21¡Ñ37) orthogonal arrays were selected for the biological industrial sludge and biological municipal sludge, respectively. Among others, applied mechanical pressure and time, electrode array, and electrodewatering time were operating parameters of concern. Test results showed that a 10-15% increase of dewatering efficiency for both sludges was obtained for the parallel circuit and parallel series circuit. However, the filtrate quality deteriorated, particularly in pH, turbidity, and chemical oxygen demand. In addition, due to ohmic heating the temperature of filtrate might raise to 80 ¢Jor even higher depending on the operating conditions employed. Thus, the filtrate should be recirculated back to the wastewater treatment system for proper treatment. To find out the significant controlling factors and optimal operating conditions for electrodewatering in a more scientific manner, the final sludge cake moisture and energy consumption for each test was subjected to formal analysis and analysis of variance. For biological industrial sludge, the flocculant type and applied filtration pressure were found to be the most significant controlling factors for the final sludge cake moisture, whereas the applied electric field strength for the power consumption. In the case of biological municipal sludge, however, the electrode array was the most significant controlling factor for both final sludge cake moisture and power consumption. At last, the optimal operating conditions theoretically obtained for electrodewatering were subjected to the respective verification tests for both biological industrial sludge and biological municipal sludge. Test results showed that a final sludge cake moisture of 67.1¡Ó3.9% and energy consumption of 72.6 kWh/ton dry solids were obtained for the former sludge, whereas 68.1¡Ó3.4% and 18.6 kWh/ton dry solids for the latter sludge. These results validated the predictions made by the Taguchi method. Therefore, it may conclude that electrodewatering is technically and economically feasible for treating both biological industrial sludge and biological municipal through the electrokinetics-assisted filter press system employed in this work.

The removal of toxic and heavy metal contaminants from aqueous waste streams and industrial effluents is one of the most important environmental issues being faced the world over. In order to combat this problem, the commonly used procedures for removing metal ions from dilute aqueous streams include chemical precipitation, ion exchange, reverse osmosis and solvent extraction. However, these techniques have certain disadvantages such as incomplete metal removal, high reagent and energy requirements, generation of toxic sludge or other waste products that require disposal. The hazardous wastes generated from metal mining and smelting operations also need to be decontaminated before entering the ecosystem. Chromium contamination of soil and ground water is a significant problem worldwide. The extensive distribution of this pollutant is due to its numerous industrial applications such as metal plating, alloying, leather tanning and wood industry. Cr (VI) is toxic and carcinogenic in nature while Cr (III) is innocuous. Conventional chromium removal techniques involve reduction to the Cr (III) form and subsequent precipitation as its hydroxide. However, disposal of the solid sludge remains a problem. The search for alternative and innovative treatment techniques has focussed attention on the metal uptake capacities of various microorganisms such as yeast, algae, fungi and bacteria. It is well documented that microbial biomass is capable of adsorbing metal ions from aqueous solution even when the cells have been killed. In the present investigation, the potential of utilising a gram positive, neutrophilic, facultative anaerobe like Bacillus polymyxa, in the bioremoval of Cr (VI) and Cr (III), has been assessed under different conditions. The growth of Bacillus polymyxa has been studied in the presence of varying concentrations of chromium ions. Subsequently, adaptation of the bacteria to Cr (VI) and Cr (III) has also been carried out. The biological reduction of Cr (VI) and its biosorption have been monitored during the growth of the unadapted and 2 ppm Cr (VI) adapted strains. The bioremoval of Cr (VI) and Cr (III) has also been assessed using the metabolic products obtained during bacterial growth. Detailed investigations have been carried out to determine the bioremoval efficiencies of both living and non-living cells of Bacillus polymyxa, with respect to Cr (III) and Cr (VI). The various parameters influencing the bioremoval of chromium by the cells, such as time, pH, wet biomass loading and initial metal concentration, have been studied. Electrokinetic studies on the bacterial cells, before and after interaction with Cr (VI) and Cr(III)have been carried out. The morphological changes induced in the bacterial strains consequent to interaction with Cr (III) and Cr (VI) have been examined by scanning electron microscopy. The results of the present investigation revealed that bioreduction of Cr (VI) was feasible during the growth of both adapted and unadapted bacteria. The time taken for 90% bioremoval was 72 h in the case of the unadapted strain, whereas with the adapted strain only around 48 h were required to achieve comparable results. The metabolic products obtained by enzymatic bacterial action were also found to be efficient in bringing about the bioremoval of Cr (VI). The bioremoval efficiency was marginally better when a lower concentration of Cr (VI) was used. Over 80% bioremoval was achieved in about 10 h using 2 ppm Cr (VI) while almost 48 h were necessary for a similar amount of removal to be effected using 5 ppm Cr (VI). In the case of the metabolite obtained from the adapted strain, complete removal of 2 ppm Cr (VI) was possible in 24 h. The living cells of Bacillus polymyxa were not only able to accumulate Cr (VI) but were also capable of bioreduction to the Cr (III) form, when the pH was in the range of 1.5 to 4. The maximum bioremoval of about 75% of Cr (VI) was observed at pH 2, with 45% being attributed to bioreduction, with an equilibration time of 48 h. In the case of Cr (III) nearly 90% uptake could be achieved at a natural pH of 5.5, equilibration time of 24 h and using 1 g of wet biomass. Biosorption was the only method of removal present in the non-living system. In the case of nonliving biomass, the optimum conditions for maximum Cr (VI) removal (65%) were pH 2, equilibration time of 12 h and a biomass loading of 1 g, whereas for Cr (III), the maximum uptake of about 97% occurred at an initial pH of 5, equilibration time of 12 h and 0.4 g wet biomass. The non-living cells showed a better efficiency in removing Cr (III), while the living cells exhibited a greater tendency towards the bioremoval of Cr (VI) than the non-living ones. Electrokinetic measurements revealed that consequent to interaction with Cr (VI) or Cr (III), significant surface modification was brought about on the cells of Bacillus polymyxa. Further, the isoelectric point was found to be shifted towards less acidic values after interaction with Cr (III) or Cr (VI). The probable mechanisms of the bioremoval processes are highlighted.

Infectious diseases resulting from bacterial pathogens are the most common causes of patient morbidity and mortality worldwide. The rapid identification of the pathogens and their antibiotic resistances is crucial for proper clinical management. However, the standard culture-based diagnostic approach requires a minimum of two days from the initial specimen collection to result reporting. As a consequence, broad-spectrum antibiotics are often prescribed under the worst-case assumption without knowledge of the pathogens or their resistances. The current clinical practice results in improper treatment of the patient and causes the rapid emergence of multi-drug resistant pathogens. A rapid diagnostics system has therefore been developed which performs hybrid electrokinetic sample preparation and volume reduction, for single-cell antimicrobial susceptibility testing (AST). The system combines multiple electrokinetic forces for sample preparation, which reduces the sample volume for over 3 orders of magnitude and minimizes the matrix effects of physiological samples for enhanced sensitivity. The device is integrated with a single-cell AST system with microfluidic confinement and electrokinetic loading to phenotypically determine the bacterial antibiotic resistance at the single-cell level. The applicability of the system has been demonstrated for performing direct AST with urine and blood samples within one hour, enabling rapid infectious disease diagnostics in non-traditional healthcare settings.

Molecular analysis of free circulating (fc)DNA has the potential to change the face of medicine, specifically in cancer diagnostics and in monitoring the efficacy of cancer treatments. In this study, a microfluidic device using AC electrokinetics is developed for rapid concentration and detection of fcDNA from blood. The device concentrates fcDNA using a combination of AC electrothermal flow and dielectrophoresis. The electrothermal fluid motion drives fcDNA towards the center of the electrode where dielectrophoretic trapping occurs. Once fcDNA is collected at the center, the concentration in the sample can be determined by fluorescent analysis using an intercalating dye binding to the double-stranded DNA. Effects of operating parameters are investigated to optimize the device's design. The electrokinetic device isolates high molecular weight DNA and can distinguish from low molecular weight DNA. Quantitative detection of fcDNA in physiologically relevant concentrations is demonstrated toward rapid diagnostics of cancer and monitoring of treatment efficacy.

Established techniques for the detection of pathogens, such as bacteria and viruses, require long timeframes for culturing. State of the art biosensors rely on the diffusion of the target analyte to the sensor surface. AC electric fields can be exploited to enhance the sampling of pathogens and concentrate them at specific locations on the sensor surface, thus overcoming these bottlenecks. AC electrokinetic effects like the dielectrophoretic force and electrothermal flows apply forces on the particle and the bulk fluid, respectively. While dielectrophoresis forces pathogens towards a target location, electrothermal flows circulates the fluid, thus replenishing the local concentration. Numerical simulations and experimental proof of principle demonstrate how AC electrokinetics can be used to collect model bioparticles on an antibody functionalized selective surface from a heterogeneous solution having physiologically relevant conductivity. The presence of parallel channels in a quadrupolar microelectrode design is identified as detrimental during the negative dielectrophoretic collection of bioparticles at the centre of the design while simultaneously providing secondary concentration points. These microelectrodes were incorporated onto the surface of a novel cantilever design for the rapid positive dielectrophoretic collection of Escherichia coli bacteria and enabled the subsequent detection of the bacteria by measuring the shift in the resonance frequency of the cantilever. Finally, a proof of principle setup for a Raman coupled, AC electrokinetically enhanced sampling and detection of viruses is shown where the presence of M13 phages are identified on a selective antibody functionalized surface using Raman spectroscopy. / Thesis (Ph.D, Chemical Engineering) -- Queen's University, 2012-01-30 19:23:48.958

The increasing production and usage of engineered nanoparticles has raised concerns about potential ecological and human exposures and the risks these novel materials may pose. Nanoparticles are often manufactured with an organic macromolecular coating, and they will attain further coatings of adsorbed natural organic matter (NOM) in the environment. The overall objective of this thesis is to improve our ability to quantify the effects of adsorbed coatings on nanoparticle fate in the environment. The physicochemical properties of the coating or the adsorbing macromolecule are expected to strongly mediate the surface interactions, and hence the environmental fate, of coated nanoparticles. To this end, this research focuses on assessing a coating characterization method and applying extensive characterization of NOM coatings to enable the development of correlations to predict nanoparticle deposition onto model environmental surfaces and aggregation. The first objective is to assess the applicability of a soft particle electrokinetic modeling approach to characterize adsorbed layer thickness, which contributes to repulsive steric forces that will affect nanoparticle deposition. A statistical analysis determined that high uncertainty in fitted layer thicknesses will limit this approach to thin, low-charged coatings (for which it may be advantageous to typical sizing methods such as dynamic light scattering). Application of this method in experimental studies further confirmed the model limitations in estimating layer thicknesses and the inability of this measurement (and other commonly measured properties) to fully explain nanoparticle deposition behavior. These results demonstrated the need for improved detail and accuracy in coating characterization. The second objective is to correlate the properties of NOM to its effects on gold nanoparticle aggregation, with particular focus on the role of heterogeneity or polydispersity of the NOM molecular weight. Multiple types of NOM collected from representative water bodies and soils were used, both in whole and separated into molecular weight (MW) fractions, and characterized for chemical composition and MW distribution. While average MW of the NOM provided good correlation with aggregation rate, the highest MW components were found to contribute disproportionately in stabilizing nanoparticles against aggregation, highlighting the importance of measuring and accounting for high MW components to explain nanoparticle aggregation. However, an outlier from the MW trend was identified, emphasizing the need for additional characterization (e.g. of reduced sulfur content or the conformation of the adsorbed NOM) to fully explain the effects of NOM on nanoparticle aggregation. Altogether, this research provides novel knowledge that will guide future application of characterization methods to predict attachment processes for coated nanoparticles in the environment.