Theoretical Analysis and Experimental Study of Time-Varying Electric Field and Electrostatic Adhesion Force Generated by Interdigital Electrode Arrays

A model is presented for the analysis of the electric field and electrostatic adhesion force produced by interdigital electrodes. Assuming that the potential varies linearly with distance in inter-electrode gaps, the potential distribution on the electrode plane is obtained by taking the first-order Taylor series approximation. The expressions of electric field components are then derived by solving the Laplace equation for the electrical potential in each subregion. The electrostatic adhesion force is calculated using the Maxwell stress tensor formulation. The dynamic properties of the electric field and electrostatic adhesion force are assessed by evaluating the transient response of the field and force under a step in applied voltages. To verify the model developed, an experimental study is carried out in conjunction with the theoretical analysis to evaluate the adhesion performance of an electrode panel on a glass pane. A double tracked wall climbing robot is designed and tested on various wall surfaces. The limit of the approximation method of the inter-electrode potential is discussed. It is found that vacuum suction force is involved in the adhesion. The influence of this vacuum suction force on electrostatic adhesion is also discussed. The results of this work would provide support for theoretical guidelines and system optimization for the electrostatic adhesion technology applied to wall climbing robots.

For electrostatic adhesion on a dielectric material, the electrostatic adhesion force gradually increases to a steady value after the voltage exerted onto the interdigital electrodes. However, little has been addressed to reveal governing mechanisms behind this dynamic phenomenon. In this paper, a theoretical model is presented for analysis of the dynamic properties of electrostatic adhesion on dielectric materials. Firstly, the electric field was derived by solving the Laplace equation of the electrical potential for each sub-area using general solution and boundary conditions. Then, the electrostatic adhesion force was obtained using the Maxwell stress tensor formulation. Finally, the dynamic properties of the electric field and electrostatic adhesion force were assessed by evaluating the transient response of the field and force under a step in applied voltages. Experimental studies for verification were conducted by evaluating the adhesion performance of an electrode panel on three different substrate plates: glass, wood and Polyvinylidene Fluoride (PVDF). Results from these experiments are highly consistent with the theoretical model. The overall results of this paper provide theoretical guidelines for systematic optimization of electrostatic adhesion technology in various application scenarios, such as electrostatic chucks, electrostatic suspension systems and electroadhesive wall-climbing robots.

Effect of charge transfer on electrostatic adhesive force under different conditions of particle charge and external electric field

The micromanipulation of objects of size between 10 μm and 1 mm is often disturbed by the adhesion between the contacting surfaces. The electrostatic force in the contact alone can significantly perturb the micromanipulation by its important adhesion effect. The electrostatic adhesion force is influenced by many factors, i.e., the materials of the contacting bodies and the topography of the contact surface. Micromanipulation by contact involves applying a squeezing force to hold the object firmly which causes the contact surface to deform, flattening the surface asperities. The prime purpose of this work is to study the influence of the plastic deformation of the surface asperities on the electrostatic adhesion force considering the contact between two conductors. A single-level model of the surface roughness was considered in this study, approximating the shape of a surface asperity by a sine function. A simulation tool based on the finite element method was used to compute the elastic–plastic deformation of the model surface asperities during micromanipulation. Another numerical model was used to compute the electrostatic adhesion force acting on the surface asperities in the initial and in the deformed configurations. A magnification factor of up to 20 was obtained for the electrostatic force in the contact evaluated numerically, related to the flattening of the surface asperities, which can potentially lead to perturbations when releasing the object. The observed effect is merely a lower bound of the real one, considering the simplifying assumptions of the numerical models.

Electric field detachment of a nonuniformly charged dielectric sphere on a dielectric coated electrode

Fabrication and electrochemical properties of an interdigitated array electrode in a microfabricated wall-jet cell

In the electrophotographic process, electric fields are used to detach and move charged toner particles from one surface to another. In principle, electric field detachment occurs when the applied electrostatic force overcomes the toner adhesion force to a surface. For triboelectrically charged toner, many measurements have indicated that the electrostatic adhesion force is much greater than that calculated for a uniformly charged dielectric sphere, suggesting that the surface charge distribution on a toner particle is nonuniform. In the present work, the physics of the electrostatic force is described and a dumb-bell type charge distribution on triboelectrically charged toner particles is proposed as an approximation of nonuniformly charged particles. The electrostatic force on an isolated toner particle with a dumb-bell type charge distribution is computed by means of a recently developed computational method based on a Galerkin finite-element technique. The effect of the electrode spacing on the electric field detachment of charged toner particles is examined in particular. The results show that the magnitude of electrostatic force is rather insensitive to the electrode spacing when the particle is nonuniformly charged, unless the spacing is so small that the counter electrode is nearly touching the particle. The electrostatic force for detaching a charged particle is shown to become maximized when the particle charge and applied field strength satisfy a certain relationship. Formulas are also derived for the minimum electric field strength and the corresponding particle charge that are required for the maximized electrostatic detaching force to overcome the non-electrostatic components of adhesion. For triboelectrically charged toner particles, the components of the electrostatic force components are shown to be much greater than nonelectrostatic force components. If the particle charge is proportional to the particle surface area and the non-electrostatic force component is relatively insignificant, the detachment of toner particles in response to an applied electric field should be independent of the particle size.

Quantitative Analysis of Homogeneous Electrocatalytic Reactions at IDA Electrodes: The Example of [Ni(PPh2NBn2)2]2+

he successful operation of many beyond-lithium-ion battery chemistries depends on efficient formation of the solid electrolyte interphase (SEI). During the first charge cycles, electrolyte is reduced at the anode surface and insoluble degradation products form a passivating layer, allowing ion transport while preventing additional electrolyte degradation. The solubility of degradation products affects the efficiency of SEI formation. In particular, electrolyte degradation products are more soluble in sodium-ion systems compared to lithium. As a result, sodium-ion batteries are subject to lower columbic efficiency, faster capacity fade, and higher resistance growth than lithium-ion. Addressing this limitation requires improved understanding of degradation product solubility, including methods to measure the relative concentration of dissolved electrolyte products. While differences in solubility have been studied through ex-situ spectroscopic techniques, in-situ detection of soluble degradation products can allow increased understanding of SEI dynamics and enable real time evaluation of the efficiency of SEI formation. 2 Interdigitated electrode arrays are frequently used for sensitive detection of electroactive species. Interdigitated electrode arrays (IDAs) make use of small diffusion lengths between electrodes to allow for a collector-generator arrangement, yielding similar behavior to rotating ring-disk electrodes without the noise of rotation, risk of SEI shearing or need for bulky equipment.3 IDAs are subject to increased feedback current, also known as redox cycling, due to diffusion of products from the collector back to the generator.4 This is useful in the detection of products in very low concentrations but is not desirable for accurate prediction of SEI formation efficiency. Here, we fabricate customized designs of IDAs with a high aspect ratio of Wgen­ to Wcol (10-40:1) using photolithographic techniques. We are able to achieve a low feedback (1-1.1 X) while maintaining relatively high collection efficiency (25-40%). Through this work we demonstrate electrochemical monitoring of soluble products by chronoamperometric detection at the collector during SEI formation at the generator. Utilizing this technique, it is possible to observe the proportion of electroactive soluble degradation products formed as a function of potential and monitor changes in the system with time. (1) Dahbi, M.; Yabuuchi, N.; Kubota, K.; Tokiwa, K.; Komaba, S. Negative Electrodes for Na-Ion Batteries. Phys. Chem. Chem. Phys. 2014, 16 (29), 15007. https://doi.org/10.1039/c4cp00826j. (2) Iermakova, D. I.; Dugas, R.; Palacín, M. R.; Ponrouch, A. On the Comparative Stability of Li and Na Metal Anode Interfaces in Conventional Alkyl Carbonate Electrolytes. J. Electrochem. Soc. 2015, 162 (13), A7060–A7066. https://doi.org/10.1149/2.0091513jes. (3) Aoki, K.; Morita, M.; Niwa, O.; Tabei, H. Quantitative Analysis of Reversible Diffusion-Controlled Currents of Redox Soluble Species at Interdigitated Array Electrodes under Steady-State Conditions. J. Electroanal. Chem. 1988, 256 (2), 269–282. https://doi.org/10.1016/0022-0728(88)87003-7. (4) Odijk, M.; Olthuis, W.; Dam, V. A. T.; Van Den Berg, A. Simulation of Redox-Cycling Phenomena at Interdigitated Array (IDA) Electrodes: Amplification and Selectivity. Electroanalysis 2008, 20 (5), 463–468. https://doi.org/10.1002/elan.200704105. Figure. SEI formation current at generator (blue) and amperometric detection at collector (orange) as a function of time Figure 1

In this paper, a versatile, rapid and reproducible method for patterning different cell types based on negative dielectrophoresis (n-DEP), without any special pretreatment of a culture slide, has been described. An interdigitated array (IDA) electrode with four independent microelectrode subunits was fabricated with indium-tin-oxide (ITO) and used as a template to form cellular micropatterns. A suspension of C2C12 cells was introduced into the device between the upper slide and the bottom IDA. In the present system, the n-DEP force is induced by applying an ac voltage (typically 12 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pp</sub> , 1 MHz) to direct cells toward a weaker region of electric field strength. The cells aligned above one of the bands of IDA within 1 min since the aligned areas on the slide were regions with the lower electric field. The application of an ac voltage for 5 min allows the cells to adsorb onto the cell culture slide. After disassembling the device and removing excess cells, the culture slide was assembled again with the IDA electrode, and was rotated 90deg relative to the previous setup. The second cell type was patterned in lines using the same method as with the first set of cells, forming a grid pattern on the slide.

In the electrophotographic process, charged toner particles are transferred from one surface to another with an electric field. To enable electric field transfer of toner, the externally applied field strength must be greater than a threshold value so that the coulombic force can overcome the toner adhesion force at the residing surface. In this work, the threshold field strength to detach a uniformly charged dielectric sphere and the electrostatic adhesion force are determined efficiently by using the Galerkin finite element method to simultaneously solve the Laplace equation for the field distribution and an overall constraint equation for the force balance. This computational method is applicable to various problem configurations. For illustrative purposes, however, the authors consider the axisymmetric problem of electric field detachment of a uniformly charged dielectric sphere on a dielectric coated electrode. Their analysis is particularly focused on the dependence of the threshold detachment field strength and electrostatic adhesion force on the dielectric coating thickness and gap between electrodes.

Dielectrophoresis (DEP) cell separation technology is an effective means of separating target cells which are only marginally present in a wide variety of cells. To develop highly efficient cell separation devices, detailed analysis of the nonuniform electric field's intensity distribution within the device is needed, as it affects separation performance. Here we analytically expressed the distributions of the electric field and DEP force in a parallel-plate cell separation DEP device by employing electrostatic analysis through the Fourier series method. The solution was approximated by extrapolating a novel approximate equation as a boundary condition for the potential between adjacent fingers of interdigitated electrodes and changing the underlying differential equation into a solvable form. The distributions of the potential and electric fields obtained by the analytical solution were compared with those from numerical simulations using finite element method software to verify their accuracy. As a result, it was found that the two agreed well, and the analytical solution was obtained with good accuracy. Three-dimensional fluorescence imaging analysis was performed using live non-tumorigenic human mammary (MCF10A) cells. The distribution of cell clusters adsorbed on the interdigitated electrodes was compared with the analytically obtained distribution of the DEP force, and the mechanism underlying cell adsorption on the electrode surface was discussed. Furthermore, parametric analysis using the width and spacing of these electrodes as variables revealed that spacing is crucial for determining DEP force. The results suggested that for cell separation devices using interdigitated electrodes, optimization by adjusting electrode spacing could significantly enhance device performance.

The utilization of two-working-electrode mode of interdigitated array (IDA) electrodes and other two-electrode systems has revolutionized electrochemical detection by enabling the simultaneous and independent detection of two species or reactions. In contrast to conventional two-potential electrodes, such as the rotating ring disk electrodes, IDAs demonstrate analogous yet vastly improved performance, characterized by remarkable collection efficiency, sensitivity, and signal amplification resulted from the 'feedback' effect. In recent decades, the research surrounding IDAs has garnered escalating interest due to their attractive attributes. This review centers its focus on the recent development on the fabrication of IDA electrodes as well as their applications leveraging the unique electrochemical and structural features. In fabrication, two critical breakthroughs are poised for realization: the achievement of reduced dimensions and the diversification of materials. Established fabrication methods for IDA electrodes encompass photolithography, inkjet printing, and direct laser writing, each affording distinct advantages in terms of size and precision. Photolithography enables the creation with finer structures and higher resolution compared to others. Inkjet printing or laser writing provides a simpler, more cost-effective, and straightforward patterning process, albeit with lower resolution. In terms of applications, IDAs have found utility in diverse fields. This review summarizes recent applications based on their fundamental working principles, encompassing redox cycling, resistance modulation, capacitance variations, and more. This specialized tool shows great promise for further development with enhanced properties. It is also important to note that, micron- or sub-micron-sized IDAs generally cannot be reused, as their small structures cannot be polished. Therefore, controlling the cost of IDA fabrication is crucial for promoting their broader application. Additionally, the distinctive electrochemical properties of 'feedback' effect is often underappreciated. The high sensitivity of IDA electrodes, arising from the 'feedback' signal amplification mechanism, holds significant potential for the detection of species with short lifetimes or low concentrations.

The efficient formation of the solid electrolyte interphase (SEI) plays a central role in the performance and lifetime of beyond-lithium-ion battery chemistries. The SEI forms as a result of insoluble products generated during electrolyte undergoes reduction at the anode surface during initial charge cycles. A preferential SEI prevents additional electrolyte reduction while allowing facile ion transport, while an improperly formed SEI can severely limit battery lifetime through continuous electrolyte reduction. Electrolyte degradation products are more soluble in sodium-ion systems compared to lithium, impacting the stability of the SEI. As a result, sodium-ion batteries are subject to lower columbic efficiency, faster capacity fade, and higher resistance growth than lithium-ion[1]. Better understanding of the formation and dissolution of soluble degradation products, including methods to measure the relative concentration of dissolved electrolyte products, is necessary to overcome these limitations.While differences in solubility have been studied through ex-situ spectroscopic techniques, in-situ detection of soluble degradation products can allow increased understanding of SEI dynamics and enable real-time evaluation of the efficiency of SEI formation[2]. Interdigitated electrode arrays(IDAs) are frequently used for sensitive detection of electroactive species. These electrode arrays make use of small diffusion lengths between electrodes to enable communication over short time scales. When used in a collector-generator arrangement, IDAs yield similar electroanalytical capabilities to rotating ring-disk electrodes without the noise of rotation, risk of SEI shearing, or need for bulky equipment [3]. The small diffusion lengths of these devices also result in overlapping diffusion layers, causing a redox cycling effect[4]. While this is useful in the detection of products in very low concentrations but is not desirable for accurate prediction of SEI formation efficiency. Using photolithographic techniques we have fabricated a novel, highly-asymmetric interdigitated electrode array that utilizes geometry to bias diffusion and limit feedback while maintaining collection efficiencies greater than 25%.Through this work, we demonstrate electrochemical analysis of soluble products by chronoamperometric and cyclic voltammetry detection at the collector during SEI formation at the generator. Using this technique, we can generate characteristic signatures of electrolytes with preferential and detrimental SEI formation characteristics and observe the proportion of electroactive soluble degradation products formed as a function of potential at the working electrode.(1) Dahbi, M.; Yabuuchi, N.; Kubota, K.; Tokiwa, K.; Komaba, S. Negative Electrodes for Na-Ion Batteries. Phys. Chem. Chem. Phys. 2014, 16 (29), 15007. https://doi.org/10.1039/c4cp00826j.(2) Iermakova, D. I.; Dugas, R.; Palacín, M. R.; Ponrouch, A. On the Comparative Stability of Li and Na Metal Anode Interfaces in Conventional Alkyl Carbonate Electrolytes. J. Electrochem. Soc. 2015, 162 (13), A7060–A7066. https://doi.org/10.1149/2.0091513jes.(3) Aoki, K.; Morita, M.; Niwa, O.; Tabei, H. Quantitative Analysis of Reversible Diffusion-Controlled Currents of Redox Soluble Species at Interdigitated Array Electrodes under Steady-State Conditions. J. Electroanal. Chem. 1988, 256 (2), 269–282. https://doi.org/10.1016/0022-0728(88)87003-7.(4) Odijk, M.; Olthuis, W.; Dam, V. A. T.; Van Den Berg, A. Simulation of Redox-Cycling Phenomena at Interdigitated Array (IDA) Electrodes: Amplification and Selectivity. Electroanalysis 2008, 20 (5), 463–468. https://doi.org/10.1002/elan.200704105.Figure 1. (a) ) Voltage curves for charge at 1C and discharge at C/10 on generator and (b) product detection via cyclic voltammetry at the collector. Figure 1

Introduction Aptamers are DNA or RNA molecules that bind to targets (proteins, small compounds, cells etc.) with high affinity and specificity. In particular, DNA aptamers have attractive properties for construction of biosensors; they are chemically-synthesized and easy to be modified by functional group with low production cost. Aptamer-introduced materials have been utilized to develop numerous biosensors, and indeed, proteomic microarray-based platform using modified aptamers is commercially available. Due to its several useful properties, we have employed DNA aptamers for development of electrochemical biosensors. We focused on glucose dehydrogenases (GDHs), enzymes have been already adopted by industries and utilized in commercially available glucose monitoring systems, as signal transducers for electrochemical detection of targets by aptamers. In addition, it is well-known that thrombin cleaves substrate peptide conjugated electroactive compound, and aptameric enzyme subunit (AES), a homogeneous detection method based on enzymatic activity, was developed utilizing thrombin in our laboratory. Thus, we are developing electrochemical measurement platform for AES based on thrombin activity. In this presentation, we describe electrochemical target detection systems based on GDH-labeled DNA aptamers and AES utilizing thrombin. Methods 1. Electrochemical detection of targeted molecules using GDH-labeled aptamers We developed GDH-employed electrochemical aptasensors with three method of GDH-labeling to DNA aptamer; (i) avidin-biotin interaction1,2, (ii) GDH-binding aptamers3,4 and (iii) GDH-fused zinc finger protein (unpublished result, but the enzyme-labeling method using enzyme-fused zinc finger protein has been already reported5.) DNA aptamers were labeled with recombinant PQQGDH from Acinetobacter calcoaceticus or FADGDH from Aspergillus flavus. GDH-fused zinc finger protein was expressed in Escherichia coli BL21(DE3) and purified by affinity chromatography. Thiolated aptamers or biotinylated antibody were immobilized on gold electrode. After incubation with target molecules, the gold electrode was immersed into GDH-labeled aptamer solution. We measured the response current to addition of glucose and m-PMS. 2. Electrochemical measurement of thrombin activity via interdigitated array electrodes We aim at measurement of target molecules by using interdigitated array (IDA) electrodes. IDA electrodes are suitable for redox cycling, which lead to achieve highly sensitive detection with a combination of a redox agent. Therefore, we measured thrombin activity using substrate peptide conjugated p-aminophenol. p-aminophenol is characterized as a redox agent. First, thrombin activity without inhibition for p-aminophenol-conjugating peptide was measured by IDA electrodes and the increased sensitivity via redox cycling was confirmed. Next, the activity with inhibition was investigated. Results and discussion 1. We found significant decreasing enzymatic activity of PQQGDH conjugated with streptavidin, but measurement of thrombin was attained and the detection threshold was indicated as 40 nM due to high catalytic efficiency of original PQQGDH. GDH fusing zinc finger protein showed 50% of enzymatic activity compared to the wild type GDH. DNA aptamer binds to GDHs did not affect the enzymatic activity. Sandwich-type sensing platform was utilized for protein detection, and target measurement based on the structural change was utilized for detection of adenosine. We successfully detected 500 pM-15 nM of VEGF and 0.2-5 mM of adenosine, respectively. 2. We observed changes in the electric current on addition of the electroactive substrate in the thrombin concentration dependent way. Under the redox cycling condition, level of the current was twice as high as the usual, non-redox cycling condition. Inhibition of thrombin was also found by addition of DNA aptamers for thrombin. These results suggested that a combination of electrochemical measurement of thrombin activity with IDA electrodes and thrombin inhibition system utilizing AES has the potential to achieve simplified diagnostic method in the future. Acknowledgement A part of this work was supported by AMED-SENTAN program.