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Nowadays, there are various electrokinetic phenomena which are utilized in a wide range of applications, ranging from microfluidics and colloid and interface science to electrochemistry. However, even after 200 years of research on electrokinetic phenomena, there are still open questions with respect to fundamental understanding. The focus of this thesis is on three different phenomena, i.e., streaming potential, streaming current and electroosmosis. Hence, the thesis is divided in two parts: The first part focuses on the applicability of the classical Helmholtz-Smoluchowski theory on streaming potential and streaming current measurements of poly(methyl methacrylate) (PMMA) wafers, to infer the zeta potential of this substrate in contact with liquids of defined pH and ionic strength. In detail, we perform electrical impedance spectroscopy measurements to infer the electrical resistance in a PMMA microchannel and derive novel correlations for the electrokinetic characterization of the substrate. We conclude that convection can have a significant impact on the electrical double layer configuration which is reflected by changes in the surfaces conductivity. The second part of the thesis is concerned with electroosmotic flows in porous substrates where we develop a phenomenological correlation which is based on dimensional reasoning. A large set of experiments is carried out using a relatively simple and cost-effective setup including different sintered packed beds of borosilicate microspheres. A centre-of-mass model of the experimental setup allows for the interpretation of various effects. Streaming current measurements result in a correlation for the zeta potential of borosilicate depending on ionic strength and pH of the liquid. Finally, a quantitative expression for electroosmotic flow in packed beds of granular material is derived from the experiments. This correlation can be employed with other materials as well. / Thesis (Master, Chemical Engineering) -- Queen's University, 2014-06-11 10:58:11.557

Measuring low electrical currents with high precision is critical across various fields, particularly in applications like microfluidic biosensing. Traditional digital multimeters (DMMs) are inadequate for low current measurements due to their high input burden and limited resolution. Therefore, more sensitive instruments like electrometers and picoammeters are often required but are typically expensive. This thesis explores the design and construction of a cost-effective, portable, and user-friendly picoammeter based on a transimpedance amplifier (TIA), capable of measuring currents in the picoampere (pA) range with a resolution of 1-5 pA and minimal noise. The constructed picoammeter has a maximum input current range of ±1.5 nA.  A prototype was built on a soldering board to validate the design, which was then translated into a practical printed circuit board (PCB) layout. The device is powered by batteries to ensure low noise levels and enable isolated operation. An Arduino microcontroller was used to interface with the circuit, manage data acquisition, and enable real-time visualisation of the measured current data on a computer.  Simulation results confirmed the theoretical performance of the circuit, and experimental validation showed RMS noise levels of less than 0.3 pA under controlled conditions and up to 3 pA when measuring streaming currents from a microchip. Despite a slight underestimation of input currents due to resistor tolerances, calibration adjustments successfully corrected these discrepancies.  The total cost of the materials used in constructing the picoammeter was significantly less than the cost of commercially available devices. While commercial devices offer higher precision and additional functionalities, the developed picoammeter demonstrates how application-focused solutions can provide comparable accuracy and noise characteristics to commercial devices for a fraction of the price.

La caractérisation des propriétés électriques et diélectriques des membranes d’UF et de NF constitue une étape essentielle pour la compréhension de leurs performances de filtration. Une nouvelle approche a été développée pour déterminer les propriétés diélectriques d’une membrane de NF par spectroscopie d’impédance. Celle-ci repose sur l’isolement de la couche active du support membranaire et sur l’utilisation de mercure comme matériau conducteur, ce qui nous a permis de prouver que la constante diélectrique de la solution à l’intérieur des nanopores est inférieure à celle de la solution externe. Deux configurations de cellule (fibres immergées dans la solution d’étude ou fibres noyées dans un gel isolant) ont été étudiées pour la réalisation de mesures électrocinétiques tangentielles sur fibres creuses et la solution autour des fibres s’est avérée influencer à la fois le courant d’écoulement et la conductance électrique de la cellule. De plus, la contribution importante du corps poreux des fibres au courant d’écoulement ne permet pas de convertir cette grandeur en potentiel zêta luminal. Les propriétés intéressantes de ces membranes ont finalement été mises à profit pour décontaminer des solutions contenant des ions métalliques. Les performances de dépollution, en termes de rétention des polluants et d’impact écotoxicologique, ont été étudiées sur des solutions synthétiques et un rejet issu de l’industrie du traitement de surface. Bien que les performances de rétention aient été remarquables, la toxicité de l’effluent réel n’a pu être totalement annihilée. Une étude approfondie de la rétention des polluants non métalliques s’avère donc nécessaire. / The characterization of electrical and dielectric properties of UF and NF membranes is an essential step to understand their filtration performance. A new approach has been developed to determine the dielectric properties of a NF membrane by impedance spectroscopy. This is based on the isolation of the membrane active layer and the use of mercury as conductive material, which allowed us to prove that the dielectric constant of the solution inside nanopores is lower than that of the external solution. Two cell configurations (fibers immersed in the solution or fibers embedded in an insulating gel) were investigated for the implementation of tangential electrokinetic measurements with hollow fibers and the solution around the fibers was found to influence both streaming current and cell electrical conductance. Moreover, the important contribution of the fiber porous body to the streaming current does not allow the conversion of the latter to luminal zeta potential. The advantageous properties of these membranes were finally used to decontaminate solutions containing metal ions. Decontamination performances in terms of both pollutant retention and ecotoxicological impact were studied on synthetic solutions and a discharge water from surface treatment industry. Although retention performances were remarkable, the toxicity of the real effluent could not be totally annihilated. A thorough study of the retention of non-metallic contaminants is thus required.

A l'interface solide-liquide, des réactions physicochimiques conduisent à polariser l'interface et à former la double couche électrique (DCE). La circulation du liquide transporte une partie des charges électriques de la DCE et conduit au phénomène d'électrisation par écoulement. Dans les transformateurs de puissance, constitués, entre autres, d'huile minérale et de carton d'isolement, le phénomène d'électrisation est suspecté d'être à l'origine de certaines défaillances et accidents. Dans cette problématique de risque, de nombreuses études ont été menées et ont permis de mettre en évidence l'influence de paramètres significatifs : nature des matériaux, humidité des matériaux, géométrie et vitesse de l'écoulement, température. Peu d'études se sont concentrées sur l'influence du champ électrique, en particulier les champs continus (DC). Même si le champ électrique généré dans les équipements de puissance est principalement alternatif (AC), il n'en est pas moins vrai que des champs électriques continus (DC) résiduels peuvent être présents, en particulier dans les dispositifs H.V.D.C (High Voltage Direct Current). L'objet du travail s'inscrit dans ce contexte et a pour but, dans une approche à la fois expérimentale et numérique, d'apporter des éléments de réponse sur le développement et le transport des charges de la double couche électrique sous contrainte de champ électrique externe. / At the solid-liquid interface, physicochemical reactions lead to the polarization of the interface and to the formation of an electrical double layer (EDL). The process of flow electrification is due to the convection of part of the electrical charges located in the EDL. In power transformers within which mineral oil and pressboard are commonly used for cooling and electrical insulation, a flow electrification phenomenon is suspected to be responsible of failures. In this hazard assessment problematic, many studies have been made and allowed identifying the influence of significant parameters: nature of materials, moisture level of materials, flow geometry and velocity, temperature. Few studies have focused on the influence of the electric filed, particularly the continuous electric fields (DC). Even though the electric field generated within power transformers is mainly alternating (AC), it is nonetheless true that residual DC electric fields may be detected (e.g. High Voltage Direct Current appartus). This present work fits in this context and aims at providing, both through an experimental and numerical approach, some answers on the development and the transport of charges from the electrical double layer under external electric field stresses.

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