Papers by Keyword: Electrokinetics

Abstract: This study explores the effects of magnetic fields on the electrokinetic behavior of reservoir fluids and their discharge characteristics under varying pressure conditions. A specialized experimental setup was designed to replicate reservoir environments, incorporating a high-pressure column, PVT bomb, electromagnet and various measurement and control instruments. Experiments were conducted to assess how different magnetic field strengths (ranging from 40 to 150 mT) influence voltage, resistance and water discharge across a pressure range of 1.6–14.4 atm. The findings indicate that magnetic fields enhance fluid behavior by improving ion mobility and electrical conductivity, which results in greater water discharge and more stable fluid flow at elevated pressures. This research offers important insights into how magnetic fields can improve fluid transport in porous media, with promising implications for advancing enhanced oil recovery (EOR) methods.

Abstract: The paper summarizes utilization of nanoparticles (NP) in concrete for enhancing its mechanical, transport or other properties. The first part is devoted to review of NPs used in fresh concrete mixtures that have been reported previously in the literature while the second part shows original results from utilization of nanoparticles as healing agents for reparing of existing concrete structures. In the second case, nanoparticles are delivered to concrete via electrokinetic principle by using their surface charge provided in colloidal solutions. Particles are transported in the pore liquid of concrete due to electric field applied between the concrete surface and steel reinforcement. In this way, distressed concrete can be repaired, cracks sealed and risk of corrosion diminished. The injection of NPs can be complemented with extraction of chlorides that are the main deteriorating chemicals in reinforced concrete structures. Finally, the paper shows a framework developed for the electrokinetic transport of ionic species in concrete applied to chloride extraction from concrete and how it can be modified also for transport of nanoparticles.

Abstract: Conventional techniques for detection of bacteria/cell and assessment of cancer cell typically use DNA techniques, Western blot and ELISA kits that are high cost, complicated processes and long time consuming. Our researches focus on rapid, portable, simple and highly sensitive separation and detection of cells/bacteria/biomolecules for field-use diagnosis. An ideal portable biosensor (molecular or whole cells detections) unit must have several important features: rapid detection time (<10 minutes), high sensitivity (pM level for molecular detection, 10³ cells/ml for whole cell detection), high specificity, small and inexpensive instrumentation configuration. Electrochemical impedance/conductance sensing is preferred over optical detection because of cost and portability concerns. Cancer cell detection using heterogeneous medical samples require continuous isolation, sorting, and trapping of the target bioparticles and immunocolloids within a diagnostic chip. We have developed several electrokinetic strategies to rapid separation, concentration and detection of cells/bacteria/biomolecules in a microfluidic chip using such as dielectrophoresis (DEP), traveling-wave dielectrophoresis (twDEP) and electrohydrodynamics (EHD). Several key techniques we done, which on a rapid/simple/label-free detection platform for the highly sensitive on-chip separation/identification/quantification will be introduced in this paper.

Abstract: Conventional electrophoretic deposition is being combined with pulse electric fields to deposit yttria stabilized zirconia from ethanol based suspensions onto bondcoated turbine alloys for thermal barrier coatings. The addition of the pulse electric fields to the electrophoretic process has demonstrated the capability to decrease the coating roughness, minimize hydrolysis, and decrease coating edge effects commonly encountered in electrokinetic and electrochemical deposition processes. Subsequent to the electrophoretic deposition process the green body coatings were subjected to a combined binder burnout and sintering process for further coating densification. The coatings have been qualified in terms of surface roughness as well as microstructure and experiments have been performed to show that the pulse EPD process can deposit TBC materials onto turbine components.

Abstract: Local electrophoretic deposition of alumina nanoparticles under external DC electric field conditions with submerged impinging jet type capillaries arranged at ion exchange membrane substrates is presented. In order to evaluate particle deposition mechanisms a mathematical model is derived describing electroosmotic pumping of electrolyte through a micrometre scaled channel. The system is governed by surficial charge discontinuities and modeled by coupled mass balances, Ohmic law, Navier Stokes, and Nernst-Planck equations. Based on the boundary conditions of bulk convective electrodiffusion the effect of the imposed surface potential on the fluid flow behaviour and on particle tracing characteristics is studied by means of numerical analysis. The following findings have been obtained. At the corner edges of the charged surficial boundaries micro-vortices are generated to build up local stagnation points onto the modeled membrane surface. Particle tracing analysis reveal that the particle movement is caused by mass transport within the membrane directed velocity field to the stagnation point. The complex electrokinetics and electrohydro-dynamics suggest further investigations at membrane pore sizes in the range of the Debye-length to model the non-linear current-voltage characteristic that has already been experimentally proven for these kind of membrane EPD systems.

Abstract: It is well known that colloid-chemical aspects, such as agglomeration processes, wetting and adsorption phenomena, have a decisive influence on the separation behaviour and coating quality of a composite plating. The following processing steps for electrocodeposition have to be considered: preparation of a stable dispersion of the particles in the electrolytic bath, transportation of the particles to the metal surface, adhesion of the particles onto the surface, incorporation of the particles in the metal matrix. Celis [1,2] and Hyashi [3] could show that ion adsorption onto the particle surface is very important for electrophoretic mobility and layer quality. On the other site, Fransaer and others [2,4] showed that surface free energy plays an important role for incorporation of particles in a metal matrix. They could demonstrate that hydrophilic particles do not make contact with the electrode, probably due to repulsive hydration forces. Hydrophobic particles make contact with the electrode, due to an attractive hydrophobic force. Hence it is important to have a method for estimating the hydrophilic/ hydrophobic surface properties of such particles to select a suitable surface modification strategy. A direct way to measure the surface free energy of solid particles is not available so far. Therefore, it is generally accepted to use the phenomenon of capillary penetration of liquids into porous media to determine the wetting properties of particles by measuring the penetration velocity of well-defined liquids in a powder packing. The kinetics of penetration correlates mainly to the geometric structure of the powder packing and the wettability of the particles. By using the equation-of-state approach for solid-liquid interfacial tensions the solid surface free energy of the particles can be determined [5]. In this paper, we show the usefulness of capillary penetration experiments and discuss some parameters that should be considered for the interpretation of the data. Ion adsorption processes, on the other hand, can be described by electrokinetic measurements [6,7].

Abstract: Processing of colloidal gels with electrified interfaces to form ceramic bulk and composite materials as well as coatings of complex shapes with well definded structures in the nanoscale requires the understanding of fundamental role of the coupling between hydrodynamic and electric interactions in colloidal deposition and colloidal arrangement. In this article, fundamental equations of electrohydrodynamics of membrane supported electrophoretic deposition (EPD) as well as exemplary numerical FEM-simulations of electrophoretically deposited colloidal gels are presented. Based on microfluidic physics a model is then used to study electrohydrodynamic EPD phenomena, especially electroosmotic flow incorporated with modulated surface potentials, particle interactions and electrostatic potentials. Some practical applications of EPD as well as visions of general purpose of the computational modelling results were given.

Abstract: The process of electrophoretic deposition depends strongly on the electrokinetic properties and with it the surface properties of the material that will be processed. Different additives, conditioners but also the suspending liquid influence the surface of the applied material by adsorption. Electrokinetic investigations reflect changes in properties at the outermost solid surface very sensitive. Streaming potential measurements are especially suited for studying such changes of surface chemistry at solids with different shapes. Two approaches are applicable: 1. The adsorption process was done before measuring. The result of this process should be shown. In this case it will be interesting to see differences in the functionality of the solid surface. The zeta potential will be measured versus different pH value. 2. The adsorption process will be studied directly. The zeta potential will be determined versus the concentration of the adsorptive. The second approach can be used for investigation of adsorption of multicomponent mixtures. Competing adsorption processes are detectable.