Hot microelectrodes are very small electrodes (usually 1 100 µm in diameter), which have a surface temperature much higher than the temperature in the bulk solution. In this work, the heating is achieved by applying an alternating potential of very high frequency (100 MHz 2 GHz) and of high amplitude (up to 2.8 Vrms) to the microelectrode. As a result, very fast (on the order of milliseconds) changes in the temperature of the electrolyte solution surrounding the electrode can be achieved. Due to the size of the heated microelectrodes, the hot zone in solution is small. Therefore, the solution can be easily overheated and temperatures above the boiling point can be reached.<p> The purpose of this research was to investigate and understand the phenomena occurring at ac polarized microelectrodes and to propose new applications of these electrodes. Using both steady-state and fast-scan (10 V/s) cyclic voltammetry measurements, mass transport of redox species has been studied at ac heated microelectrodes. It has been established that the convection at hot-disk microelectrodes is driven primarily by the electrothermal flow of an electrolyte solution. In addition, other effects such as ac dielectrophoresis and Soret (nonisothermal) diffusion are also observed. Numerical simulations have been employed to predict the distribution of temperature in the hot zone, the direction and magnitude of the electrothermal force and the solution flow rate, as well as the voltammetric response of hot-disk microelectrodes. The results of the simulations agree well with the experimental observations. Theoretical findings of this PhD work are very important for the understanding of the fundamentals of high temperature electrochemistry, particularly mass transport. The proposed explanation of the convection mechanism is most likely applicable not only to ac polarized microelectrodes, but also to the microwave heated microelectrodes, since the only difference between these two heating methods is in the way of delivering electrical energy (wired vs. wireless). The results of the studies of Soret diffusion indicate that it contributes significantly to mass transfer of redox species at hot microelectrodes. Taking into account that the magnitude of the Soret effect has been considered negligible by other electrochemists, the results obtained in this work prove the opposite and show that Soret diffusion affects both the faradaic current and the half-wave potential of the redox reaction. Therefore, the Soret effect can not be ignored if working with hot microelectrodes.<p> Hot microelectrodes can have a number of interesting applications. The results of the initial investigations indicate that these electrodes can be successfully used in the arrangement for Scanning Electrochemical Microscopy (such a novel technique is termed Hot-Tip SECM). In addition, the observed dielectrophoretic and electrothermal convection effects can enhance the performance of the electrochemical sensors based on hot microelectrodes. This can lead to the improvement of the detection limits of many biologically important analytes, such as proteins, bacteria and viruses.

Rapid diagnosis of infectious disease and timely initiation of proper clinical antibiotic treatment is the determinant in obtaining the optimal clinical outcomes and reducing emergences of multidrug-resistant organisms. In particular, acute infections require the detection to be accomplished in limited time with high sensitivity due to the low concentration of organisms causing the infections. Real-time Polymerase Chain Reaction can provide quantitative identification of specific genetic materials and has revolutionized clinical microbiology laboratory diagnosis. It is becoming a standard for infectious disease detection. However, most real-time PCR instruments on the market are bulky, fragile and costly due to their delicate optical components, which restricted their use to point-of-care application. Modern microfluidic and sensing technology provide a transition from benchtop real-time PCR to miniaturizable, robust, and portable real-time PCR devices to achieve rapid, low-cost, and efficient point-of-care diagnosis. In this work, an innovative electrokinetic PCR (EK-PCR) platform that combines AC electrothermal flow (ACEF) and Joule heating induced temperature gradient to implement thermal cycling for DNA amplification is discussed. In addition, in situ electrochemical sensing is incorporated in the EK-PCR chamber for real-time monitoring of the DNA concentration toward quantification of the initial copies of the DNA template. EK-PCR can improve the energy efficiency with minimized total thermal mass and remain high amplification efficiency. More importantly, it represents a highly integrated strategy for portable point-of-care devices.

Thesis (Ph. D.)--Florida State University, 2004. / Advisor: Dr. Danuta Leszczynska, Florida State University, College of Engineering, Dept. of Civil and Environmental Engineering. Title and description from dissertation home page (viewed Jan. 14, 2005). Includes bibliographical references.

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 171-180).

The world’s growing population results in increased energy needs that cannot yet be fully supported by the renewable sources of energy. These modern conditions and restraints have created the need to further research methods to enhance the recovery of resources previously unavailable due to technical and/or economic reasons and to reduce the environmental impacts of using fossil fuels. In this dissertation, applications of electrokinetic phenomena for the improvement of subsurface energy resource extraction are investigated using experimental and numerical tools. Electrodialysis is proposed as a method of pre-treatment of the flow-back water produced during fracturing stage of shale gas extraction. The method targets the reduction of Total Dissolved Solids levels in the flow-back water so that it can either be treated further or be reused directly. The treatment and reuse of the flow-back water can potentially improve the sustainability of the shale gas extraction, controlling the amounts of water used and the general environmental footprint of the process. In addition, the electrically assisted oil recovery is investigated as a potential technique for the enhancement of oil extraction, especially for the case of heavy crude oil. The high viscosity and low mobility of heavy crude oil render it almost impossible or not economical to extract. The method uses the application of low electrical field (direct current) to the oil reservoir to facilitate and increase the oil recovery by taking advantage of the mechanisms involved in electrokinetic phenomena.

Nanofluidics is an emerging field with many science and engineering applications. The physics of material transport through nanochannels are of interest in filtration, sensing, device miniaturization, and biomimetics. To address such ambitions with nanofluidic tools will require advancements in our understanding and control over nanofluidic systems. This work contributes to electrokinetic phenomena, characterization techniques, and applications in nanofluidics. Ion transport data through nanopipettes are used to validate a finite element model for nonlinear electrokinetic flows. With the model, we conclude that asymmetric surfaces induce fluid vortices and provide insight into supporting mathematical techniques. We then establish nanobubble-plugged nanopipettes as promising ionic devices due to the electrokinetic effects of three-phase interfaces. Using cryogenic transmission electron microscopy, ion current measurements, and extensive physical modeling, we conclude that nanobubble plugs are metastable, slow-growing, and induce strong current rectification and enhancement. All these insights let us study microbial surfaces using electrokinetic phenomena detected by a scanned nanopipette. Over immobilized Pseudomonas aerugonsa cells and Δphz-type biofilms, we detect topographic and surface charge properties due to voltage-dependent signals through a scanned nanopipette probe. Our efforts establish a fast hopping probe scanning ion conductance microscopy technique for long-range surface charge detection. Finally, we use an integrated carbon nanotube channel to demonstrate how solid-state charge can drive electrokinetic flows through Coulomb drag coupling.

No description available.

Student Number : 0418764K - MSc (Eng) dissertation - School of Civil and Environmental Engineering - Faculty of Engineering and the Built Environment / Increasing quantities of finer wastes often contain reactive sulphide minerals and high water contents that pose stability and environmental concerns. This study investigates how electrokinetic process can be improved, to make it more viable towards dewatering finer coal slurries. In the electrokinetic process, a direct current induces the movement of water out of a porous material. A wooden test box was filled up to two-thirds with fine coal slurries. Electrokinetic Geotextiles (EKGs) and brass were used as electrodes. The conducting wires were attached to each electrode and connected to a DC source to form an electro-osmosis cell. Current was passed through the cell and water moved to the cathode where it was withdrawn. The dewatering efficiencies ranged from 13.13 to 109.84 ml/Ah. The energy consumptions ranged from 5.23 to 14.03 kWh/m3 and are in line with those recorded by Johns (2005). Conductivity and pH measurements were taken. EKGs performed better than brass electrodes.

No description available.

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.