Non-conductive Surface Research Articles

Engineering nano-thin electrospun coatings for air filters with high filtration and breathability by nanofiber charge control

A modified electrospinning design was introduced to overcome the limitation in non-uniformity of the nanofibrous coating on the surface of non-conducting, statically charged polypropylene microfibers. By manipulating the charge distribution over the non-conducting surface via variations in the polarity of the Taylor cone and the electrospinning geometry, it was possible to obtain a uniformly adherent and thin nanofibrous coating over a large area to achieve a layer-by-layer simultaneous deposition of + ve and −ve fibers onto a non-conducting membrane. The uniformity and quality of this nanocoating was found to have a direct effect on particle filtration and breathability of air filters. The filter showed a high particle filtration efficiency of 96 % for 0.3 µm particles, with excellent breathability.

Continuous electro-growth of a hierarchically structured hydrogel on a non-conductive surface

Designing hydrogels with hierarchically ordered structures is of significance for biomimetic applications through simulating natural biological soft tissues.

Locally boosted Li2S nucleation on VO2 by loading carbon quantum dots for soft-packaged lithium-sulfur pouch cells.

VO2 affords ultrafast polysulfide adsorption on account of its oxidation potential, which matches the sulfur working window (1.7-2.8 V). Nevertheless, its nonconductive surface limits direct sulfur conversion. Herein, we gently load carbon quantum dots on VO2 to increase direct Li2S nucleation by enhanced electron conductivity. As a result, the soft-packaged lithium-sulfur pouch cell yields a capacity retention of 88.8% at 0.5C after 100 cycles and a decay rate of 0.17% per cycle over 200 cycles at 2C. The cell energy density of the multilayer cell is up to 386.1 W h kg-1.

Study of Damage Prediction of Carbon Fiber Tows Using Eddy Current Measurement.

When manufacturing fiber-reinforced composites, it is possible to improve the quality of fiber steel fire and reduce the number of cracks in the finished product if it is possible to quickly identify the defects of the fiber tow. Therefore, in this study, we developed a method to identify the condition of carbon fiber tow using eddy current test (ECT), which is used to improve the quality of composite materials. Using the eddy current detection sensor, we checked the impedance results according to the condition of the CF tow. We found that the materials of the workbench used in the experiment greatly affected the ECT results, so it is necessary to use a material with a non-conductive and smooth surface. We evaluated the impedance results of the carbon fiber at 2 mm intervals using the ECT sensor and summarized the impedance results according to the fiber width direction, presenting the condition of the section as a constant of variation (CV). If the condition of the carbon fiber tow was unstable, the deviation of the CV per section was large. In particular, the deviation of the CV per section was more than 0.15 when the arrangement of the fibers was changed, foreign substances were formed on the surface of the fibers, and damage occurred in the direction of the fiber width of more than 4 mm, so it was easy to evaluate the quality on CF tow.

The varied roles of pilA-N, omcE, omcS, omcT, and omcZ in extracellular electron transfer by Geobacter sulfurreducens.

Geobacter sulfurreducens mediates extracellular electron transfer (EET) reactions with different substrates, such as solid-phase Fe(III)-containing minerals, anodes and the cells of Geobacter metallireducens. To compare their roles in EET, the pilA-N, omcE, omcS, omcT and omcZ genes of G. sulfurreducens were systematically deleted. All mutants showed impaired and varied ability to form biofilms on nonconductive surface. Deletion of omcE also impaired bacterial ability to reduce ferrihydrite, but its impacts on the ability for anode reduction and the co-culture of G. metallireducens-G. sulfurreducens were minimal. The mutant without omcS showed diminished ability to reduce ferrihydrite and to form the co-culture, but was able to regain its ability to reduce anodes. Deletion of omcT, omcZ or pilA-N alone impaired bacterial ability to reduce ferrihydrite and anodes and to form the co-culture. Deletion of all tested genes abolished bacterial ability to reduce ferrihydrite and anodes. Triple-deletion of all omcS, omcT and omcZ abolished the ability of G. sulfurreducens to co-culture with G. metallireducens. However, deletion of only omcZ or pilA-N or both omcS and omcT abolished the ability of G. sulfurreducens without hydrogenase gene hybL to co-culture with G. metallireducens, which show their indispensable roles in direct electron transfer from G. metallireducens to G. sulfurreducens. Thus, the roles of pilA-N, omcE, omcS, omcT and omcZ for G. sulfurreducens in EET vary substantially, which also suggest that possession of PilA-N and multiple cytochromes of different structures enables G. sulfurreducens to mediate EET reactions efficiently with substrates of different properties.

Programmable droplet manipulation enabled by charged‐surface pattern reconfiguration

AbstractProgrammable droplet manipulation based on external stimulation is in high demand in various modern technologies. Despite notable progress, current manipulation strategies still suffer from a common drawback such as single control means of modulating the external stimulation input, which leads to huge challenges in sophisticated and large scale‐up droplet handling. Herein, a unique pattern‐reconfiguration‐driven droplet manipulation method is developed on conductive/nonconductive pattern surfaces under charge deposition. Contactless charge deposition induces the “edge barrier” phenomenon at the boundaries of conductive/nonconductive patterns, analogous to an invisible and tunable wall guiding droplet behaviors. The edge barrier effect can be flexibly tuned by the nonconductive surface pattern. Thus, with charge deposition, surfaces are endowed with protean control functionality. The design of conductive/nonconductive patterns can effectively enable multifunction droplet manipulations, including track‐guided sliding, sorting, merging, and mixing. Moreover, dynamical pattern reconfiguration drives programmable fluidics with sophisticated and large scale‐up droplet handling capabilities in a low‐cost and simple approach.

Electrochemical Deactivation of Switchable Catechol-Containing Smart Adhesive from Nonconductive Surfaces

The feasibility of deactivating and reactivating a catechol-containing smart adhesive electrochemically while in direct contact with a nonconductive surface was explored in this work. The adhesive was coated over an aluminum mesh-attached poly(dimethylsiloxane) (AM-PDMS) substrate. The aluminum mesh served as an electrode to apply electricity through the adhesive. A silver (Ag) counter electrode was coated in the periphery of the adhesive–substrate interface to deactivate the adhesive attached to the nonconductive surfaces including glass and poly(methyl methacrylate) (PMMA) substrates. The deactivation of the adhesive was performed with the application of up to 20 V of applied electricity utilizing the Ag electrode as a cathode and the aluminum mesh as an anode. The adhesion strength of the adhesive toward nonconductive surfaces decreased by 98% after in situ application of electricity. The deactivation rate was tunable with the applied voltage level, exposure time to the applied voltage, surface area of the adhesive interface, and aluminum mesh size. The deactivated adhesive was reactivated electrochemically by reversing the electrode polarity up to 3 cycles utilizing catechol–boronate complexation chemistry.

Low-frequency impedance of ion-exchange membrane with electrically heterogeneous surface

Understanding of the effect of membrane/electrode surface heterogeneity on the electrochemical behavior of membrane/electrode systems in conditions of current-induced concentration polarization is an important issue. In this paper, low-frequency electrochemical impedance spectra (EIS) of electrically heterogeneous ion-exchange membranes (IEMs) are studied experimentally and theoretically. A 2D model for calculating these spectra is proposed. Non-stationary ion transport through a heterogeneous membrane and two adjacent diffusion layers is studied. The corresponding mathematical problem is solved numerically and analytically under conditions of zero DC bias of the applied AC signal. It is shown that at sufficiently low frequencies, the impedance spectrum of a heterogeneous IEM is described by the finite-length-Warburg-type impedance. However, in the range of relatively high frequencies, a nose-shaped element appears on the complex plane plot. This element reflects an increase in the system resistance due to a higher concentration polarization of the boundary solution caused by nonconductive surface areas. An exact analytical solution describing the impedance is found in the case where the diffusivities of anion and cation are the same. The form of this solution is convenient for the experimental data analysis. A good quantitative agreement between the calculated and experimental impedance spectra for several commercial and specially prepared heterogeneous membranes is established.

Unconventional Surface Charging Within Deep Cavities on Airless Planetary Bodies: Particle‐In‐Cell Plasma Simulations

AbstractSurface charging properties of a nonconducting surface that has a deep cavity and is in contact with the solar wind plasma are investigated by means of the particle‐in‐cell plasma simulations. The modeled topography is an abstract representation of deep depressions found on the irregular surfaces of solid planetary bodies. The simulations have revealed unconventional charging features in that the cavity bottom is charged up to positive values even without any electron emission processes such as photoemission, provided that the surface location is accessible to a portion of incoming solar wind ions. The major driver of the positive charging is identified as drifting ions of the solar wind plasma, and an uncommon current ordering where ion currents exceed electron currents is established at the innermost part of the deep cavity. This also implies that the deep cavity bottom may have a positive potential of several hundred volts, which is similar in magnitude to the kinetic energy of an ion drift motion. The present study also clarifies the role of photoelectrons in developing the distinctive charging environment inside the cavity. The photoemitted electrons can no longer trigger positive charging at the cavity bottom, but rather exhibit the effect of relaxing positive potentials caused by the solar wind ions. The identified charging process, which is primarily due to the solar wind ions, is localized at the depths of the cavity and may be one possible scenario for generating intense electric fields inside the cavity.

Experimental investigation on deposits of ER70S-6 wire on SiO2 substrate using non-transferred arc-based wire arc additive manufacturing

Recent trends in additive manufacturing (AM) are to produce geometrically complex structures at minimal wastage of material, time and cost without sacrificing part quality and mechanical performance and to introduce ease in processing and part removal. Here, a non-transferred arc (NTA)-based wire arc additive manufacturing (WAAM) system has been developed to achieve the above objectives, where the arc is only generated between tungsten electrode and consumable filler wire. No electrical contact with the substrate facilitate deposits even on the non-conductive substrate surface, which helps to remove the final deposits easily. The influence of deposition parameters (welding current, voltage, wire feed speed (WFS) and travel speed) on response characteristics (bead uniformity, height deviation, droplet diameter, and droplet transfer frequency) is studied on a multi-performance level using grey relational analysis (GRA). Then, single- and multi-bead layer is fabricated over SiO2 substrate for ease in part removal after complete fabrication. WFS is referred to as a key deposition parameter that influences all deposition characteristics. It has been observed that NTA-based WAAM results in high bead uniformity with minimal spatter and low bead height difference between start and exit arc point. Complete ferrite microstructure with few pearlites is observed on the deposits with similar elemental composition on the top, bottom and interface surfaces. X-ray diffraction (XRD) study reveals ferrite diffraction planes ({110}, {200}, {211} and {220}) with no intermetallic formations on deposits. Also, compressive residual stress with less variation in crystallite size, stress, strain and microhardness among the top, bottom and lateral deposit surfaces indicates the fabricated part’s isotropic nature.

The current magnetization hypothesis as a microscopic theory of the Ørsted magnetic field induction

A wire that conducts an electric current will give rise to a circular magnetic field (the Ørsted magnetic field), which can be calculated using the Maxwell–Ampere equation. For wires with diameters in the macroscopic scale, the Maxwell–Ampere equation is an established physical law that can reproduce a range of experimental observations. A key implication of this equation is that the induction of Ørsted magnetic field is a result of the displacement of charge. A possible microscopic origin of Ørsted magnetic induction was suggested in [J. Mag. Mag. Mat. 504, 166660 (2020)] (will be called the current magnetization hypothesis (CMH) thereupon). The present work establishes computationally, using simplified wire models, that the CMH reproduces the results of the Maxwell–Ampere equation for wires with a square cross section. I demonstrate that CMH can resolve the apparent contradiction between the observed magnetic field and that predicted by the Maxwell–Ampere equation in nanowires, as was reported in [Phys. Rev. B 99, 014436 (2019)]. The CMH shows that a possible reason for such contradiction is the presence of non-conductive surface layers in electric conductors.

Investigation of magnetic flux density on conducting and non-conducting cylindrical surface using magnetic sensor

This paper highlights the investigation of the magnetic flux density on the conducting and non-conducting surfaces by providing magnetic and electric field as a source of excitation. Measuring the leakage magnetic flux density and flux within low frequencies on conducting and non-conducting surfaces is useful for the non-invasive measurement methods. The Helmholtz coil is used to excite the cylindrical surface in two ways: magnetic and electric field excitation. The Hall Effect sensor is used to detect the strength of magnetic flux density on the cylindrical surface. Direction of flux lines, distribution of magnetic flux density and electric field around the surface explained through the simulation results. The results are graphically plotted by varying the current for the magnetic field excitation and by varying the voltage for electric field excitation. Hall voltage is varying linearly with increase in current and constant with increase in voltage for the non-conducting cylindrical surface for various locations of cylindrical surface. Simultaneously, Hall voltage is linearly increases and decreases for the excitation of voltage and current for the conducting cylindrical surface is presented through the graphs.

CFRP composite drilling through electrical discharge machining using aluminum as fixture plate

Recent developments in manufacturing require holes on composite materials, especially on the carbon fiber reinforced polymer (CFRP) with smooth hole periphery, low delamination, burr formation, taper, better circularity, and a high processing speed. Its non-conductive surface (epoxy layering) limits its machining through electrical discharge machining (EDM). To overcome this limitation, an aluminum fixture has been designed to guide the copper electrode of EDM for producing holes on a CFRP sheet of 1 mm thickness at low machining complexity, cost, time, delamination, burr in hole periphery and without affecting the material’s surface quality and performance. Even components with high geometrical complexity can also be drilled through this approach. Here, a multi-quality analysis called grey relational analysis is developed for examining the hole quality attributes, considering peak current, pulse on and off time, and flushing pressure as input parameters. This approach points out the optimum factor level setting and critical parameters (pulse-on time and peak current) that regulate the hole attributes (entrance and exit diameter, circularity, taper, material removal, and tool wear rate). An artificial neural network model has been designed and trained through experimental data sets. This model can also be adopted during the determination of hole quality attributes when the parameter settings are beyond a defined boundary, as the regression analysis value is very close to 1, and model performance is 4.99e-10. Peak current = 4 A, pulse-on time = 25 µs, pulse-off time=25 µs, and flushing pressure = 0.6 MPa were the optimum drilling parameters. In the initial hole, average burr length is 391.75 μm, and delamination of 539.3 μm is noticed. But burr formation is very negligible with delamination of 350.7 μm being observed with uniform circularity (0.979), low taper angle (−0.81354°), and TWR (0.000069 g/min) under optimum drilling conditions through this drilling approach.

Study of fabric knitted using Ag-coated filaments to form stretchable electrodes for use in energy storage applications

ABSTRACT Stretchable and flexible electrodes are desirable for use in mobile and wearable devices. When one surface of a fabric is non-conductive and the other surface is electrochemically active, such a fabric could potentially be used as an electrode in an electrochemical application without a separator because the non-conductive surface would prevent short circuits between the electrodes. In this study, a stretchable fabric with a conductive surface that has been knitted using Ag-coated filaments was cycled in aqueous (alkaline, acidic, and neutral) and non-aqueous (ionic liquid) electrolytes to study their electrochemical behaviors for their usability as energy storage devices. After study via cyclic voltammetry, KOH solution was selected as the most appropriate electrolyte among the four considered because the fabric showed stable oxidation and reduction peaks in this electrolyte after repetitive cycling. The Ag-based fabric electrode was also found to evolve (became stable) in this electrolyte. Electrochemical (cyclic voltammogram) and non-electrochemical (X-ray diffraction, scanning electron microscope, energy dispersive X-ray spectroscopy) characterization of the electrode were carried out. The cycling of stretchable fabric was stopped at the oxidized and reduced potential in KOH electrolyte in order to characterize the crystalline, morphological, and compositional structure of the electrode as dependent on the applied potential. The capacitances of the electrode remained similar when the timescale was increased 40-fold, indicating that the electrode has a high power density. The reaction between the fabric and OH− electrolyte was found to proceed as a ‘mixture’ of a surface- and a diffusion-controlled mechanism. The areal and specific capacitances of the electrode were found to be 46 mF cm−2 and 36 F g−1, respectively. The stretchable fabric with Ag-coated filaments could potentially be used as an electrode in a hydroxide-based electrolyte for stretchable and flexible energy storage devices.

Challenges in electroplating of additive manufactured ABS plastics

Additive manufacturing of plastics as modern technology introduces new perspectives towards exceptional structures and allows realization of contemporary designs. For those purposes a post-treatment of the components, e.g. surface coating with metals, is crucial. Electroplating on polymers, like ABS (terpolymer of acrylonitrile, butadiene and styrene), is an established industrial process applied on components manufactured by standard technologies, like injection molding. It consists of various steps – from cleaning over creating electric conductivity on the non-conducting polymer surface towards galvanic coating with metals. In this publication, the challenges in transferring this process to additive manufactured ABS components are analyzed by focusing on the surface quality. Surface quality is evaluated by macroscopic imaging and different microscopic technologies (transmission light microscopy, laser scanning microscopy and scanning electron microscopy). The success of electroplating processes on plastics strongly depends on the nature of the plastic surfaces and therefore on the additive manufacturing parameters applied. The used additive technology of fused deposition modelling is characterized by the deposition of single plastic strands. Adjustments of selected manufacturing parameters, such as the layer thickness and the overlap of the stored plastic strands, create the conditions of homogenous and well adhering metal coatings. According to the surface topology from this additive manufacturing process, pre-treatment with levelling and sealing the surface is identified as important challenge towards success and reproducibility of electroplating process.

Charge Density Fluctuations on a Dielectric Surface Exposed to Plasma or UV Radiation

Dust particles on a nonconductive surface are known to acquire electric charge and detach from the surface under plasma conditions and/or when affected by ultraviolet radiation. Similar phenomena occur as a result of electrostatic surface cleaning (shedding) as well as in nature, e.g., when observing levitation of dust particles above the lunar surface. A detachment of dust particles from the surface should occur when the electrostatic forces of their repulsion Fc exceed the sum of the gravitation Fg forces and the adhesive van der Waals FvdW forces acting on the particle on a nonconducting surface. However, a paradoxical situation usually arises: the three primary forces of different nature Fc, Fg, and FvdW, acting on a speck of dust with a characteristic size of the order of hundreds or thousands of nanometers, are completely incomparable in magnitude, herewith Fc << Fg << FvdW. In the last decade, numerous attempts have been made to explain how a particle on a nonconducting surface can acquire a charge sufficient for the electrostatic forces that arise to approach the adhesive forces’ values. However, despite some successes, many questions remain unanswered. This article presents a brief analysis of the charge appearance process on a solitary dust speck and a speck lying on the surface. To explain the detachment of dust particles from the surface caused by electrostatic forces and the accumulation of a charge on those particles sufficient for levitation, one should take into account the charge density fluctuations on the surface.

Culture of neural stem cells on conductive and microgrooved polymeric scaffolds fabricated via electrospun fiber-template lithography

We developed polymeric scaffolds that can provide both topographical and electrical stimuli on mouse neural stem cells (mNSCs) for potential use in nerve tissue engineering. In contrast to conventional patterning techniques such as imprinting, soft/photolithography, and three-dimensional printing, microgroove patterns were generated by using aligned electrospun fibers as templates, via a process denoted as electrospun fiber-template lithography. The preparation of polyvinylpyrrolidone fibers, followed by the deposition of poly(lactic-co-glycolic acid) (PLGA) and the removal of the fiber template, produced freestanding PLGA scaffolds with microgrooves having widths of 1.72 ± 0.24 μm. The subsequent deposition of polypyrrole (PPy) via chemical oxidative polymerization added conductivity to the microgrooved PLGA scaffolds. The resultant scaffolds were cytocompatible with mNSCs. The microgroove patterns enhanced the alignment and elongation of mNSCs, and the PPy layer promoted the interaction of cells with the surface by forming more and longer filopodia compared with the nonconductive surface. Finally, the neuron differentiation of mNSCs was evaluated by monitoring the Tuj-1 neuronal gene expression. The presence of both microgrooves and the conductive PPy layer enhanced the neuronal differentiation of mNSCs even without electrical stimulation, and the neuronal differentiation was further enhanced by stimulation with a sufficient electrical pulse (1.0 V).

Effect of Physisorption of Collector on Activation of Flotation of Sphalerite

The studies into the mechanism of activation of sphalerite flotation by ions of heavy metals show that neither ion exchange nor electrochemistry explain the experimental facts, namely, activation of flotation of copper mineral by lead ions, activation of sphalerite flotation by zinc, or flotation in the presence of non-conducting surface layer with silver or mercury. The authors put forward the hypothesis of activation due to the effect of physisorption of a collector in elementary event of flotation. It is possible to activate froth flotation by the products of nonstoichiometric interaction between xanthate and ions of some heavy metals. The influence of the scope of deviation from the stoichiometric relation of concentrations of xanthate and activation metal salt on the collectability of the interaction products is described. The activation efficiency of the interaction products is estimated using the criterion of ‘surface flow thickness’ of the film of collector derivatives at the gas-liquid interface.

Percolation model for conductivity of composites with segregation of small conductive particles on the grain boundaries

The percolation model of electrical conductivity of a two-component medium, formed by a mixture of conductive small and non-conductive large particles with the adhesion of small particles to the surface of large ones and subsequent mixture compaction, is suggested. The model describes two main aspects. The first is a strong lowering of percolation threshold as a result of segregation of the conductive component on the non-conductive particle surface. The second is the calculation of the critical indices describing the power-law dependence of conductivity on composition as a consequence of percolation effects on the surface conductivity of large particles. Surface conductivity arises due to segregation of the conductive component and leads to threshold in a three-dimensional grid of conductive surfaces.

MHD Free Convective Flow along Vertical Oscillatory Plate with Radiative Heat Transfer in the Presence of Hall Current and Heat Source

MHD free convective flow with oscillations of an infinite non-conducting vertical flat surface through a porous medium with Hall current in a rotating system was studied. The governing equations of the model were converted into dimensionless form. Analytical solutions for velocity and temperature were obtained with the help of the Laplace transform method. Graphs and tables are used in this paper to show the influence of various parameters on temperature, skin friction and velocity. It was observed that changes in plate oscillation, porous medium, radiation and Hall current have significant effects on fluid motion. Further, the skin friction near the surface is increased by the radiation parameter. The results obtained have large implications in the engineering and science fields.