Conduction Path Research Articles

Fabrication of carbon nanotube/ titanium dioxide nanomaterials-based hydrogen sensor using novel two-stage dielectrophoresis process

The porosity and large surface area of carbon nanotubes (CNTs) made them a candidate active material for gas sensing applications. However, the responsivity and sensitivity of CNTs toward hydrogen are lower than those of metal oxide semiconductor materials such as TiO2. The addition of TiO2 to CNTs is found to increase the sensitivity of the resulting composite material at the expense of increasing the resistance. This paper presents a new dielectrophoresis (DEP) process to fabricate nanoparticle-based hydrogen sensors at room temperature. The simple and low-cost process is based on tuning the AC signal frequency to deposit different nanoparticles in stages, forming a composite sensing layer across interdigitated electrodes (IDE). The sensing layers have been characterized using field emission scanning electron microscopy (FESEM), energy-dispersive X-ray (EDX), and atomic force microscopy (AFM). Sensors fabricated with only CNTs showed low resistance and weak sensitivity of less than 2%. The sensitivity has increased to 3.42% when CNTs are deposited together with TiO2 in a single stage. However, the sensor shows high resistance because TiO2 particles interrupt the conduction paths of CNTs. A high sensitivity of 15.78% and a low resistance of ∼524 Ω have been achieved when CNTs are deposited individually in the first stage, and followed by depositing the TiO2 in the second stage. This work provides a proof-of-concept that the two-stage DEP enhances the performance of the sensor in terms of sensitivity and resistance compared to single-stage DEP, which is highly desirable in fabricating composite and multi-layer sensing materials.

Improvement of Constructal Optimization for “Volume-Point” Heat Conduction Based on Uniformity Principle of Temperature Difference Fields

The uniformity principle of temperature difference fields (TDFs) is applied in this study to improve the constructal optimization for “volume-point” heat conduction based on entransy dissipation rate (EDR) minimization without the premise of an optimal last-order construct, and the constructal optimization algorithm based on EDR minimization is simplified in this paper. The results further prove that the uniformity principle of TDF is consistent with entransy theory. The constructal optimization of “volume-point” heat conduction based on EDR minimization is conducted not only to lower the average temperature but also to obtain a more uniform TDF distribution. Through comparing the optimal results based on EDR minimization without the premise of an optimal last-order construct with those based on maximum temperature difference (MTD) minimization, some criteria and formulas for designing conductivity paths based on EDR minimization and MTD minimization are proposed, and the idea and method of improving constructal optimization via the variational principle are proposed.

Thermally insulating carbon nanotubes and copper ferrite based porous polydimethylsiloxane foams for absorption-dominant electromagnetic interference shielding performance

The exponential growth of the electronic and communication industry in the last 50 years raised serious concerns about electromagnetic (EM) pollution. Consequently, suitable composite materials for electromagnetic interference (EMI) shielding have been developed to reduce EM pollution. In the present work, carbon nanotubes (CNT) and copper ferrite (CuFe2O4) nanoparticle-based porous polydimethylsiloxane (PDMS) composite foams were prepared using the baking soda template method. The PDMS foam acts as the 3-dimensional (3D) porous network, CNT gives the required conductive path and magnetic CuFe2O4 provides the necessary magnetic loss, so that the resultant foams achieved high EMI shielding through the absorption mechanism. Without the inclusion of CuFe2O4, the total EMI SE of the PDMS foam is lower than 20 dB, while various contents of the added CuFe2O4 improve the EMI SE up to 32 dB at a thickness of 3 mm. In addition, the thermal insulation properties are also reported and the resultant material shows a moderately low thermal conductivity of 0.046 W m−1 K−1. These characteristics of the composite foam highlight the strong absorption-dominated EMI shielding and thermal insulation performance, allowing it to successfully meet a wide range of applications.

Short-range order in amorphous oxygen-deficient TaOx thin films and its relation to electrical conductivity

Thin films of tantalum oxide hold promising functional properties for electronic applications such as resistive random-access memory. For this aim, correlating the structure and charge transport properties of oxygen-deficient derivatives is crucial. Here, using electron scattering measurements from nanoscale volumes in a transmission electron microscope (TEM), we report how oxygen content affects short-range order in amorphous TaOx thin films, where 1.34 ≤ x ≤ 2.50. By extracting the bond lengths, we observe that the dominant type of Ta–Ta distances change with decreasing oxygen content from next-nearest-neighbor, ∼3.8 Å, to nearest-neighbor, ∼3 Å. We relate this decrease to the Ta–O polyhedral network within the film, namely decreasing oxygen content increases the presence of TaO5 at the expense of TaO6 polyhedra. The reduction in oxygen content is accompanied by a significant reduction of electrical resistivity of the films from over 4.3 × 103 to (4 ± 0.05)×10−3 Ω × cm. In particular, we observe a sharp percolative decrease in resistivity of three orders of magnitude, at x ∼ 1.9. Ta oxidation states, measured by x-ray photoelectron spectroscopy, suggest that the main polyhedral building block within the TaO2.5 film is TaO6, while in oxygen-deficient films, the relative fractions of TaO5 polyhedra and metallic Ta increase. At even lower oxygen content, x ∼ 1.34, TEM and x-ray diffraction detect crystallites of Ta with cubic and metastable tetragonal structures. We propose that TaO5 polyhedra and Ta crystallites increase conductivity due to direct bonding of Ta atoms, as manifested by nearest-neighbor Ta–Ta bond length, thus enabling conductive paths for charge transport.

Confined dissipation cage in dual-shell structured Ti3C2Tx@CNTs/Ni hollow spheres for lightweight and broadband electromagnetic wave absorption

Ti3C2Tx can dissipate energy well due to its high conductivity, but at the expense of severe electromagnetic (EM) wave reflection, which is exacerbated by self-stacking. Despite various attempts to tackle this problem, the excessive isolation of Ti3C2Tx and massive high-density inorganic components render these designs unfavorable for lightweight and broadband absorption. Meanwhile, improvements in absorption performance are related to active surface and polarization interface expansion, as well as conductive path reconstruction, but the main contributing factor remains unknown. In this work, the dual-shell structured Ti3C2Tx@CNTs/Ni-HS (hollow sphere) composites are fabricated. This structure creates a confined dissipation cage, where the CNTs/Ni shell confines the electron transfer among spheres and prevents self-restacking and the tightly contacted Ti3C2Tx shell forms an uninterrupted conductive path for effective dissipation. Therefore, Ti3C2Tx@CNTs/Ni-HS-1 exhibits a broad effective absorption band of 6.1 GHz and a minimum reflection loss of −64.6 dB at a mass ratio of only 15 wt%. Importantly, when hollow structure cracks, although large active surface and polarizable interface remain, the absorption capacity of fragmented Ti3C2Tx@CNTs/Ni-HS-1 deteriorates, indicating rational conductive path in confined dissipation cage is the main factor in achieving excellent performance. This work provides new insight for the rational design of high-performance absorbers.

Low-Temperature Adaptive Dual-Network MXene Nanocomposite Hydrogel as Flexible Wearable Strain Sensors.

Flexible electronic devices and conductive materials can be used as wearable sensors to detect human motions. However, the existing hydrogels generally have problems of weak tensile capacity, insufficient durability, and being easy to freeze at low temperatures, which greatly affect their application in the field of wearable devices. In this paper, glycerol was partially replaced by water as the solvent, agar was thermally dissolved to initiate acrylamide polymerization, and MXene was used as a conductive filler and initiator promoter to form the double network MXene-PAM/Agar organic hydrogel. The presence of MXene makes the hydrogel produce more conductive paths and enforces the hydrogel's higher conductivity (1.02 S·m-1). The mechanical properties of hydrogels were enhanced by the double network structure, and the hydrogel had high stretchability (1300%). In addition, the hydrogel-based wearable strain sensor exhibited good sensitivity over a wide strain range (GF = 2.99, 0-200% strain). The strain sensor based on MXene-PAM/Agar hydrogel was capable of real-time monitoring of human movement signals such as fingers, wrists, arms, etc. and could maintain good working conditions even in cold environments (-26 °C). Hence, we are of the opinion that delving into this hydrogel holds the potential to broaden the scope of utilizing conductive hydrogels as flexible and wearable strain sensors, especially in chilly environments.

Fabrication and Characterization of Humidity Sensors Based on PEDOT:PSS Doped with Gold and Silver Nanoparticles by Laser Ablation

This paper presents a simple, fast, and inexpensive method for the large-scale fabrication of polymer-based humidity sensors on glass substrates. The nanoparticles were synthesized using laser ablation, this is an environmentally friendly method for fabricating metal nanoparticles and provides a unique tool for nanofabrication. In this work, humidity sensing material, poly(3,4 ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) along with different kinds of nanoparticles, Au and Ag, are employed to enhance the stability and sensitivity to humidity sensing. Based on the experimental results, the TEM images show the crystallinity of the nanoparticles, indicating alloying of the nanoparticles. Based on XRD, this result indicates that the amorphous structure of PEDOT:PSS is only slightly affected by mixing with nanoparticles. According to FE-SEM analysis, the formation of interconnected crystallites facilitates the charge transport mechanism in the polymer chains due to improved conduction paths. Has been Characterization of humidity sensors Using (LCR), study the effect of humidity on capacitance at different frequencies (100[Formula: see text]Hz, 1[Formula: see text]kHz, 10[Formula: see text]kHz, and 100[Formula: see text]kHz), and the response and recovery time characteristics. The results show excellent linear and active behavior of the capacitive humidity response. Ag, PEDOT, and Au NPs have a synergistic effect, exhibiting a more extended sensing range and better stability. This work shows a high-sensitivity and low-cost sensing material for different humidity sensor applications.

Improving the interfacial bonding strength and suppressing shrinkage porosity of 6061Al/GFRTP hot-pressing joints via interfacial modification

The application of metal-plastic hybrid structures is of great significance for structural lightweight. The metal surface treatment is critical for metal-plastic joints. In this study, nanosecond laser was used to construct different microscale grooves on 6061 aluminum alloy (6061Al) surface to realize stable joints with glass fiber reinforced thermoplastic composites (GFRTP) by hot-pressing joining. The impacts of nanosecond laser processing on interfacial bonding of 6061Al/GFRTP were studied using analytical methods and finite element simulations. The results showed that the mechanical interlocking effectively improved the strength of connections. Moreover, the laser texturing patterns had different effects on promoting the wettability of metal surface and improving the heat conduction path. During the hot-pressing joining process, the poor wettability of molten GFRTP on untextured metal surface and different solidification rates at various molten positions led to the formation of shrinkage, which reduced the bonding area and induced stress concentration. When the pitch distance of textured grooves was 0.3 mm, the porosity was reduced to 1.15 %, and the corresponding maximum bonding strength was 9.78 MPa.

Optical and Electrical Properties of Polystyrene/Poly‐methyl methacrylate Polymeric Blend Filled with Semiconductor and Insulator Nanofillers

The present study deals with the effect of adding different fillers (semiconductor and insulator) on a polystyrene (PS)/poly‐methyl methacrylate (PMMA) polymer blend using casting method. A constant content (1 wt%) of semiconductors [multiwalled carbon nanotubes (MWCNTs), polyaniline (PANI), zinc oxide nanoparticles (NPs), and titanium dioxide NPs] and insulator [silicon dioxide NPs] fillers is used. Transmission electron microscopy images for MWCNTs show that most nanotubes have an average diameter of 7–11 nm. Moreover, the average size of all metal nano‐oxides is almost 20 nm and confirmed by X‐ray diffraction. Fourier‐transform infrared spectroscopy confirms the formation and the interaction between PS/PMMA polymer blend and fillers. The structural, mechanical, optical, and dielectric properties of the prepared polymer nanocomposites are studied using different tools. Optical characteristics such as absorbance, reflection, bandgap energy (E g), and optical dielectric components (real and imaginary) are studied. These results reveal that pure 20PS/80PMMA film has E g(direct) = 4.46 eV, which drops as different fillers are incorporated into the blend. The addition of MWCNTs, PANI to the PS/PMMA blend improves the electrical conductivity due to the growth of conductive paths between the filler and the blending matrix.

Materials and Design Approaches for a Fully Bioresorbable, Electrically Conductive and Mechanically Compliant Cardiac Patch Technology.

Myocardial infarction (MI) is one of the leading causes of death and disability. Recently developed cardiac patches provide mechanical support and additional conductive paths to promote electrical signal propagation in the MI area to synchronize cardiac excitation and contraction. Cardiac patches based on conductive polymers offer attractive features; however, the modest levels of elasticity and high impedance interfaces limit their mechanical and electrical performance. These structures also operate as permanent implants, even in cases where their utility is limited to the healing period of tissue damaged by the MI. The work presented here introduces a highly conductive cardiac patch that combines bioresorbable metals and polymers together in a hybrid material structure configured in a thin serpentine geometry that yields elastic mechanical properties. Finite element analysis guides optimized choices of layouts in these systems. Regular and synchronous contraction of human induced pluripotent stem cell-derived cardiomyocytes on the cardiac patch and ex vivo studies offer insights into the essential properties and the bio-interface. These results provide additional options in the design of cardiac patches to treat MI and other cardiac disorders.

Magnetic field enhancing preferred orientation of nickel-cobalt plated carbon fibers in cement paste, with relevance to compression self-sensing

The arrangement of carbon fibers in the cement matrix affects the stability and sensitivity of the composite. This study investigated the effects of bath pH and electroless plating time on the magnetic metallization (nickel coating, cobalt coating, and nickel-cobalt alloy coating) on carbon fibers and successfully prepared the CFRCs in which the metal-plated carbon fibers could be oriented by magnetic fields. The results showed that a pH of 10 and a plating time of 6 min were favorable for reaction kinetics, with the thickness gain, conductivity, and saturation magnetization of metal coatings all being the largest. The compressive strength of the prepared composites was increased by 26.5% by adding nickel-cobalt coated carbon fibers, which is attributed to the alignment of fibers refining pore structure. The resistivity of CFRCs with metal-plated carbon fibers is one order lower in magnitude than that with uncoated carbon fiber, due to that the alignment of fibers increases the conduction connectivity by decreasing the distance of fiber-fiber and the “quantum tunneling”. The cyclic compressive loading tests showed that the resistance changed reversibly with strain, such that the degree of reversibility is higher for CFRCs with pre-magnetic treatment than those without the treatment. The piezoresistivity (strain sensitivity) of CFRCs was stronger with magnetic field-induced orientation treatment, showing that the strain sensitivity increased by 114% after pre-magnetic treatment for CFRCs containing nickel-cobalt coating. This is attributed to that the well-aligned metal-plated carbon fibers form more conduction paths along the alignment direction, such that the resistivity along this direction is more sensitive to the compressive strain parallel to this direction.

Comparative analysis of the photovoltaic cell parameters of dye-sensitized solar cells with composite photoanodes: Effect of the alien component

The synthesis of uniform PbOx-Fe2O3 nanoparticles (NPs) was carried out and mixed with commercial P25 titanium dioxide (TiO2) to fabricate a composite photoanode for enhancing adsorption and dye loading capabilities in dye-sensitized solar cells (DSSCs). The resulting composite photoanode exhibited a broader absorption band than the photoanode composed solely of pure TiO2. Amongst the different concentrations of PbOx-Fe2O3 NPs tested, the composite photoanode containing 0.1 wt% of NPs demonstrated the highest power conversion efficiency of 5.03%. It was noticed that the resistive loss was reduced in the composite photoanode, which is beneficial for minimizing energy losses within the device. However, the presence of conductive paths introduced by the NPs increased recombination and current leakage losses. A trade-off between these two types of losses needs to be carefully managed to maximize the overall performance of the DSSCs.

NMR Investigation of Water Molecular Dynamics in Sulfonated Polysulfone/Layered Double Hydroxide Composite Membranes for Proton Exchange Membrane Fuel Cells.

The development of nanocomposite membranes based on hydrocarbon polymers is emerging as one of the most promising strategies for overcoming the performance, cost, and safety limitations of Nafion, which is the current benchmark in proton exchange membranes for fuel cell applications. Among the various nanocomposite membranes, those based on sulfonated polysulfone (sPSU) and Layered Double Hydroxides (LDHs) hold promise regarding their successful utilization in practical applications due to their interesting electrochemical performance. This study aims to elucidate the effect of LDH introduction on the internal arrangement of water molecules in the hydrophilic clusters of sPSU and on its proton transport properties. Swelling tests, NMR characterization, and Electrochemical Impedance Spectroscopy (EIS) investigation allowed us to demonstrate that LDH platelets act as physical crosslinkers between -SO3H groups of adjacent polymer chains. This increases dimensional stability while simultaneously creating continuous paths for proton conduction. This feature, combined with its impressive water retention capability, allows sPSU to yield a proton conductivity of ca. 4 mS cm-1 at 90 °C and 20% RH.

Can environmental information disclosure improve total-factor energy efficiency?

Environmental information disclosure (EID) actively causes enterprises to bear responsibility for both respecting the ecology and preserving a clean environment. It not only acts as an essential way for the public to be involved in controlling environmental pollution and supervising the performance of enterprises with respect to the environment, but is also a significant method to promote the modernization of ecological and environmental governance systems as well as capacity to govern. Panel data for 285 municipalities at the prefecture level in China from 2003 to 2019 are taken for the study. By adopting the difference-in-differences (DID) method and the mediation effect model, we discuss the influence and transmission mechanisms of environmental information disclosure on total-factor energy efficiency. The performance of total factor energy efficiency is greatly facilitated by environmental information disclosure, as indicated by the results. The conclusion remains valid after being tested. The mechanism analysis shows that its conduction path mainly comes from an innovation effect, while the structural effect, marketization effect and supervision effect play relatively weak intermediary roles. Heterogeneity analyses show that the promoting effect appears to be more pronounced in non-resource-based cities, large cities and those cities that are under strong environmental regulation.

Stable resistive switching behavior of polyvinyl alcohol coating film-based memristor under multiple operating voltages by doping AgNWs

The integration of memristive effect devices for both information storage and computation can enhance the efficiency and performance of artificial intelligence (AI) systems，the memristors based on various polymers as functional layers show high application prospects. This research introduces 5 wt% silver nanowires (AgNWs) doping into the polyvinyl alcohol (PVA) memristor device, which enables stable resistive switching (RS) behavior across multiple operating voltages. Defects from PVA and AgNWs are counterbalanced by Ag ions stimulated by AgNWs and Ag top electrode, thus reducing conductive path randomness. The device demonstrates excellent cycle durability for 300 cycles and data retention for up to 104 s. Analysis of the I-V characteristic curve reveals that the current conduction mechanism is mainly related to Ohmic conduction, Space-charge-limited conduction (SCLC), and Schottky emission mechanisms. The AgNWs simplify the structure of conductive filaments (CFs) and facilitate the formation and breakage of CFs dominated by Ag atoms, leading to the conversion between HRS and LRS of the device.

Resistivity responses of sodium sulfate and sodium chloride-type loess under different water and salinity conditions.

Saline loess is widely distributed in Africa, Latin America and Asia and is characterized by wet expansion and dry shrinkage, which has a large impact on the environment. In this study, the electrical resistivity of sodium sulfate loess and sodium chloride loess with moisture content (8-24%) and salt content (0.3-2.7%) was measured by an LCR digital bridge instrument. The experimental results demonstrated a decrease in the resistivity with the increase in moisture and salt content. When the salt content was greater than 0.9%, the rate of reduction in resistivity decreased and showed a tendency to be stable. With the increase in moisture content, the water conductive path changes from water in diffusion double layer (DDL) to capillary water and finally to gravity water, which in turn leads to a gradual decrease in the rate of reduction in resistivity. At the same salt content, the resistivity of sulfate loess is higher than that of chloride loess. This study analyses the resistivity changes of two kinds of salt-bearing loess under different water and salinity conditions, which has certain guiding significance for environmental monitoring and pollutant assessment based on resistivity data.

PEDOT:PSS stabilized paper-based piezoresistive sensor for wearable electronics

As a key component of electronic skins, flexible pressure sensors have attracted more and more attention because of the increasingly growing demand. Stability is a key parameter to evaluate pressure sensors, while relatively few reports have focused on it. Here, a paper-based piezoresistive sensor is developed, in which, the airlaid paper based sensing layer is modified with silver nanowires (AgNWs) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and sandwiched in between two convex electrodes. Due to the cross bonding of PEDOT:PSS membrane, the conductive paths of AgNWs networks are strengthened and stabilized, thus the stability of the sensor is found to be significantly improved. Besides, to regulate the compressibility by varying sensing layers, the performance of the proposed sensor can be further improved, and its practical application performances in healthcare pulse monitoring, tiny muscle motion, and voice recognition are demonstrated. The results confirm that PEDOT:PSS has the potential as stabilization media to AgNWs for paper-based flexible wearable electronics.

Precise Electrical Machine Stator Winding Modeling for Thermal Analysis of Efficient Cooling Concepts

<div>The current development of electric and hybrid electric vehicles has drawn more attention toward the development of electrical machines with high power densities. Though highly efficient, these machines heat up significantly during operation. By design, state-of-the-art water jacket cooling concepts remove the heat mainly through high internal thermal resistances of the electrical machine. The resulting maximum temperatures in the end winding region limit the achievable machine power output. In this study, alternative cooling concepts are presented, which efficiently use the existing heat conduction paths of an electric machine. For this purpose, two modeling methods for the stator windings were developed: a high-resolution approach that considers each individual wire and an abstract approach that uses zones of constant anisotropic thermal conductivity to specify the heat flow in the windings. Both models were used in conjugate heat transfer simulations of a long-term thermal test of the electrical machine integrated in the BMW i3. For both models the validation showed a very good agreement of simulated and measured temperatures. An evaluation of both methods showed the abstract approach to be more efficient than other simulation methods used in the current R&D. Its application for alternative cooling concepts revealed the necessary heat transfer coefficients at different fluid temperatures for a sole convective cooling of the end windings. However, it could be found that a homogeneous temperature distribution in the stator of the machine can only be achieved if a combination of water jacket cooling and convective end winding cooling is used.</div>

How does the opening of China's high-speed rail affect the spatial mismatch of haze pollution and economic growth?

A better reconciliation of haze pollution and economic growth has become the social consensus in China. The development of China's economy and air quality will be significantly impacted by its efforts to create high-speed rail (HSR). Based on panel data from 265 prefecture-level cities in China from 2003 to 2019, this paper investigates how the opening of HSR affects the spatial mismatch of haze pollution and economic growth by using the spatial mismatch index model, multi-period difference-in-differences (DID) model, and intermediary effect model. We find that the spatial mismatch in China has an overall decreasing trend. And its spatial agglomeration is dominated by low levels. Further empirical analysis shows that HSR opening can effectively restrain the spatial mismatch. Even after some robustness tests and endogenous treatment, the conclusion is still valid. In addition, population density, FDI, and industrial structure are also explicit factors affecting the spatial mismatch. Second, there is significant heterogeneity in the impact. This is reflected in the fact that HSR opening can suppress the spatial mismatch of service-oriented cities and the eastern region, while other cities and regions have no noticeable effect. Third, spatial transfer of haze pollution (STHP) and balanced development of economic growth (BEG) are two important conduction paths for the opening of HSR to affect the spatial mismatch. Specifically, HSR opening can constrain the spatial mismatch by inhibiting STHP and BEG. Based on the above findings, recommendations related to promoting a better harmony between haze pollution and economic growth are proposed.

"Three-in-One" Multi-Scale Structural Design of Carbon Fiber-Based Composites for Personal Electromagnetic Protection and Thermal Management

HighlightsA multi-scale structural carbon fiber-based composite was synthesized through the assembly of one-dimensional materials.The construction of multiple conductive networks makes the composite have a strong EMI shielding performance of 73.9 dB.The reasonable design endows the composite with excellent positive and passive thermal management properties.