Search Results (3,952)

The synthesis and phase behavior of two liquid crystalline racemates containing four aromatic rings, differing in the number of methylene groups, were reported. These materials form smectic phases, as was confirmed by dielectric spectroscopy. The mesomorphic properties of the studied racemates were compared with those of the appropriate (S) enantiomers previously synthesized. Since these materials are racemic mixtures, they were subjected to chiral separation by high-performance liquid chromatography. This research was conducted on two chiral columns based on polysaccharides. We identified optimal conditions that enable the baseline separation of these racemates, which can be scaled up for preparative purposes. Then, there is no need for repeated synthesis of chiral equivalents. Full article

Aerogels represent an extraordinary class of materials characterized by remarkable properties, including an exceptionally high porosity (approximately 99.8%), minimal weight, extraordinarily low density, low thermal conductivity, a diminished dielectric constant, and a reduced refractive index. These attributes arise from their extensive micro-meter-sized pores. In recent years, there has been a notable surge of interest in carbon or carbon nanotube (CNT) based aerogels due to their compelling potential across various applications, encompassing sensors, energy systems, and catalysis, among others. In the context of our ongoing investigation, we have successfully synthesized lightweight aerogels by incorporating copper and carbon nanotubes (Cu-CNT) through electrospinning. Intriguingly, these aerogels exhibit an electrical conductivity of approximately 0.5 × 103 S/cm, positioning them within the realm of semiconductors. Concurrently, their density measures approximately 1.669 g/c.c (similar to CNTs), underscoring their notably low mass. These semi-conductive aerogels, uniquely characterized by their lightweight nature and expansive surface area (approximately 442 m²/g), manifest considerable potential across a spectrum of applications. This includes catalytic processes, energy storage mechanisms, bio-sensing technologies, thermoelectric systems, and the burgeoning domains of micro and wearable electronics. The distinctive combination of properties within these aerogels augments their suitability for these diverse applications, offering the prospect of innovative and impactful advancements in various scientific and technological arenas. Full article

Ceramics are widely evaluated for their extreme hardness, high-temperature stability, and corrosion resistance, which enable applications in harsh service environments. However, these same properties, high melting points, brittleness, and low thermal shock resistance, make conventional manufacturing of complex ceramic components difficult and expensive. Traditional processes often require costly diamond tooling or energy-intensive sintering and tend to produce only simple geometries, with significant waste material and risk of defects. Additive manufacturing (AM) has recently emerged as a promising route to fabricate intricate, near-net-shape ceramic parts without these drawbacks. By building components layer by layer, AM reduces the need for extensive machining and enables the fabrication of geometrically complex, near-net-shape ceramic structures with reduced material waste, although challenges such as porosity, interlayer defects, and cracking during post-processing remain. Nonetheless, ceramic AM technologies lag behind their metal and polymer counterparts, and significant challenges remain in achieving fully dense parts with reliable mechanical properties. This review provides an in-depth overview of the state of the art in ceramics and ceramic composite additive manufacturing. We detail the most widely used AM processes (stereolithography, binder jetting, material extrusion, powder bed fusion, inkjet printing, and direct energy deposition) and typical feedstock formulations for each technique. We examine the resulting mechanical properties (strength, toughness, hardness, wear resistance) and functional properties (thermal stability, dielectric behavior, biocompatibility) of additively manufactured ceramics, and discuss their current and potential engineering applications in the aerospace, defense, automotive, biomedical, and energy sectors. Persistent challenges, including porosity, shrinkage and cracking during sintering, achieving uniform microstructures, high process costs, and scalability issues, are analyzed, and we highlight promising future directions such as multi-material grading, integration of machine learning for process optimization, and sustainable manufacturing approaches. Despite significant progress, challenges remain in achieving fully dense structures, improving process reliability, and scaling ceramic AM for industrial applications, highlighting the need for further research in process optimization, material design, and multi-material integration. Full article

Epoxy-glass-mica composite materials are widely used as electrical insulating materials in high-voltage rotating machinery due to their layered structure and excellent dielectric properties. Taking the F-class epoxy glass with a small amount of rubber powder mica tape commonly used as the main insulation of wind turbine stator coils as the research object, 7-day, 14-day, 21-day, and 28-day low-temperature treatment tests were conducted at −50 °C. The surface morphology and chemical structure changes of the materials were characterized by SEM and FTIR, and the influence laws of low-temperature treatment on the electrical properties of the mica tape insulation materials were systematically studied. The experimental results show that the low-temperature environment will induce microcracks and interface delamination and other structural damages, but no obvious change in the chemical structure of the mica tape was observed. With the extension of the low-temperature treatment time, the electrical properties of the mica tape show a deteriorating trend, and after 28 days of low-temperature treatment, the breakdown field strength of the F-class mica tape decreased by approximately 18.5%, and the volume conductivity overall increased by about two orders of magnitude. This indicates that the microcrack defects induced by low-temperature will lead to an enhanced electrical-thermal coupling effect in the insulation structure, thereby accelerating the degradation process of the insulation material. This reveals the degradation mechanism of wind turbine stator main insulation from “structural damage” to “performance degradation” and then to “insulation aging” under low-temperature conditions, providing a theoretical basis for the design and reliability assessment of insulation systems in wind turbine generators in cold regions. Full article

Flexible electrolyte-gated synaptic field-effect transistors (EGFETs) have emerged as a promising platform for neuromorphic visual systems, owing to their low-voltage operation, diverse synaptic plasticity, and exceptional mechanical flexibility. In particular, gel-based electrolytes, including hydrogels and ion gels, play a pivotal role as functional gate dielectrics, enabling efficient ion transport and strong ion–electron coupling through electric double-layer (EDL) formation. By leveraging these unique properties at the semiconductor/gel interface, EGFETs can effectively emulate essential biological synaptic behaviors, including short-term and long-term plasticity under optical stimulation. The inherent compatibility of EGFETs with a broad range of semiconductor channels, gel electrolytes, and flexible substrates enables the development of wearable and conformable neuromorphic platforms that seamlessly integrate sensing, memory, and signal processing within a single device architecture. Recent advances in gel material engineering, such as polymer network design, ionic modulation, and nanofiller incorporation, have significantly improved ion transport dynamics, interfacial stability, and device performance. Despite remaining challenges related to ion migration stability, multi-physical field coupling, and large-area device uniformity, these developments have substantially advanced the practical potential of gel-based systems. This review provides a comprehensive overview of the operating mechanisms, gel-based material systems, synaptic functionalities, mechanical reliability, and future prospects of flexible electrolyte-gated visual synapses, highlighting their considerable potential for next-generation intelligent perception and artificial vision technologies. Full article

This study presents a capacitive sensor with a zirconium oxide (ZrO₂) coating for real-time measurement of component concentration in liquid media. The ZrO₂ layer was formed on stainless steel electrodes by magnetron sputtering, and its structural, morphological, and chemical properties were characterized using SEM, EDS, FTIR, and XRD. It was found that increasing coating thickness results in more continuous and highly crystalline layers, while reducing the influence of the substrate on surface properties. The performance of the capacitive sensor was evaluated by analysing the dependence of capacitance on frequency and NaCl concentration. The results show that the thickness of the ZrO₂ layer has a significant influence on sensor sensitivity and measurement stability. A thinner layer (~2 µm) provides higher sensitivity but is more affected by parasitic effects, while thicker layers improve measurement stability at the expense of reduced sensitivity. An optimal trade-off between sensitivity and stability is achieved at a ZrO₂ layer thickness of approximately 4 µm, ensuring sufficient sensitivity and good measurement repeatability. The results indicate that ZrO₂-modified capacitive sensors are a promising technology for monitoring liquid quality, particularly in environmental protection and industrial process control. Full article

Dielectric and magnetic spherical hollow shells are employed in many applications as standard building units. These structures are commonly subjected to size reduction to obtain a high surface area/volume ratio, a property that is in favor of specific applications. However, the size reduction enhances the importance of physical mechanisms that originate from surfaces, such as the depolarization effect. Here we tackle the problem of dielectric and magnetic spherical hollow shells, consisting of a linear, homogeneous and isotropic parent material, subjected to an external potential, $U_{ext}\left(\mathit{r}\right)$, of any spatial form (either dc (static) or ac of low-frequency (quasistatic limit)). By applying the method-of-linear-recursive-solution (MLRS) to the Laplace equation, we calculate analytically the internal, $U_{int}\left(\mathit{r}\right)$, and total, $U_{tot}\left(\mathit{r}\right)$, potentials in respect to the external one, $U_{ext}\left(\mathit{r}\right)$. From $U_{int}\left(\mathit{r}\right)$ and $U_{tot}\left(\mathit{r}\right)$ we calculate all relevant scalar and vector physical entities of interest. The MLRS unveils straightforwardly the existence of two distinct depolarization factors, $N_l=l/(2l+1)$ and $N_{l+1}=(l+1)/(2l+1)$, both depending on the degree, $l$, however not on the order, $\mathrm{m}$, of the mode of the external potential, $U_{ext}^{(l,m)}\left(\mathit{r}\right)$. These depolarization factors, $N_l$ and $N_{l+1}$, originate from the outer, $r=\mathrm{b}$, and inner, $r=\mathrm{a}$, surfaces and are accompanied by two extrinsic susceptibilities, ${\chi }_{e,l}^{ext}={\chi }_e^{}/(1+N_l{\chi }_e^{})$ and ${\chi }_{e,l+1}^{ext}={\chi }_e^{}/(1+N_{l+1}{\chi }_e^{})$, respectively. Importantly, $N_l+N_{l+1}=1$, irrespective of the degree, $l$, as it should. The properties of spherical hollow shells are investigated through analytical modeling and detailed simulations, with emphasis on application-relevant scenarios including resonance phenomena in scattering, quantitative materials characterization, and shielding/distortion. The generic MLRS strategy provides a flexible and reliable route for analyzing depolarization processes in other dielectric and magnetic building-unit geometries encountered in practice. Full article

Under the deformation potential model, the superconducting phenomenon in ABC-stacked multilayer graphene under a vertical electric field is investigated using linear combination operators and unitary transformation methods. Through the deformation potential model applied to a linear continuous medium, the effect of the external electric field is converted into the deformation potential energy of the crystal. Deformation potential phonons (LA phonons) act as propagators, generating electron–electron interactions. As the electric field increases, the ratio of the electric displacement vector to the dielectric function ($D/\epsilon$) rises, leading to an increase in the electron ground-state energy, the opening of the band gap, and an enhancement of the attractive electron–electron interaction. With further increases in the external electric field, the deformation potential constant of the crystal ($D_l$) increases. When the phonon vibration frequency ($\omega$) is around 8.5 THz, and the conditions are satisfied—where the wave vectors of different LA phonons are equal in magnitude and opposite in direction, and the electron spins are opposite—the attractive electron–electron interaction reaches its maximum ($H_{eff}$), resulting in the emergence of superconductivity. Our study also provides a new perspective for understanding the unique quantum properties—such as strong correlations, superconductivity, and ferromagnetism—in different stacking configurations like AB, ABC, and ABCA. Full article

Poly(vinyl alcohol)/chitosan (PVA/CS) biodegradable films reinforced with acid-functionalized multi-walled carbon nanotubes (f-MWCNTs) were fabricated via solution casting to investigate the effects of nanotube incorporation on structural, mechanical, thermal, dielectric, and physicochemical properties. Unlike conventional CNT-reinforced systems, this study focuses on the role of acid functionalization in improving nanotube dispersion and interfacial interactions, enabling simultaneous enhancement of multiple performance characteristics. Fourier transform infrared spectroscopy (FTIR) analysis confirmed strong intermolecular interactions between PVA/CS functional groups and carboxyl groups on f-MWCNTs, while scanning electron microscopy (SEM) revealed homogeneous nanotube dispersion at low loadings and partial aggregation at higher contents. X-ray diffraction (XRD) indicated that crystallinity was modified in a non-monotonic manner with increasing nanotube concentration due to competing nucleation and chain-restriction effects, while dielectric measurements showed an increase in dielectric constant from 3.78 to 4.27 as a result of enhanced interfacial polarization. The thermal conductivity improved from 0.195 to 0.247 W·m⁻¹·K⁻¹, and tensile strength increased from 19.8 to 24.5 MPa at 0.2 wt.% f-MWCNT, with elongation at break decreasing from 37.9% to 25.1%, reflecting increased stiffness. The degree of swelling and water solubility decreased with higher nanotube content, indicating reduced hydrophilicity and enhanced structural compactness. The results provide new insights into how surface-functionalized nanofillers can be used to tailor the multifunctional performance of biodegradable polymer nanocomposite films, highlighting their potential in advanced applications such as sustainable packaging, flexible electronics, sensors, and membrane technologies. Full article

This study utilized polysiloxane as the raw material to successfully prepare black spherical silica fillers with varying internal carbon content. Through different thermal treatment processes, a dense silica layer was formed on the particle surface, while the internal hydrocarbon groups were thermally decomposed into carbon. Four types of spherical silica with different carbon contents were systematically characterized in terms of particle size distribution (D50 ≈ 2.0 μm, D100 < 5 μm), scanning electron microscopy morphology, moisture content (<0.1%), specific surface area (~1.0–1.1 m²/g), true density (~1.90–1.97 g/cm³), carbon content, blackness (L* values), and volume resistivity. The results indicate that the prepared black spherical silica exhibits a narrow particle size distribution, low moisture content, and high electrical insulation properties. Furthermore, the prepared black spherical silica was used as a filler in a polyphenylene oxide-based binder system to fabricate copper-clad laminates (CCLs), and their dielectric properties were systematically investigated. The study found that at electric field frequencies of 1 GHz and 10 GHz, the dielectric constant (D_k) and dielectric loss (D_f) of CCLs prepared with fillers containing less than 5% carbon remained largely consistent with those of carbon-free control samples. However, the D_f of CCLs prepared with fillers containing 9.00% carbon increased nearly tenfold, indicating that when the internal carbon content of the filler exceeds a certain threshold, it adversely affects the high-frequency dielectric properties of the copper-clad laminate. Full article

Terahertz time-domain spectroscopy (THz-TDS) has emerged as a powerful tool for probing hydrated materials and biological tissues, where water dynamics dominate the dielectric response. This study focuses on improving the methodology of THz-TDS by replacing conventional cuvettes, which introduce unwanted absorption, reflections, and liquid bubbles that must be accounted for during measurement interpretation, with nitrocellulose membranes of various pore sizes. The membranes were hydrated with deionized water and sealed with food-grade cling film, and their transmission properties were measured using THz-TDS. To interpret the measurements, transfer matrix method simulations were performed using the optical constants of water reported by some experimentalists, allowing verification of our data. The findings for deionized water highlight the reliability of the methodology. Our results demonstrate that nitrocellulose membranes provide stable and reproducible transmission measurements in good agreement with theoretical reference models, supported by weight retention studies and reproducibility tests conducted in spatial, temporal, and random measurement conditions. These improvements contribute to the development of more robust THz-TDS approaches for hydrated biological materials and suggest future applications in non-invasive tissue hydration monitoring and biomedical diagnostics. Full article

Electromagnetic (EM) radiation emitted by various sources can cause malfunctions or damage to other electronic devices. Composite materials are widely used for EM field shielding. This work presents and analyzes the dielectric properties of 3D-printed composites containing carbon nanotubes (CNTs) and barium titanate (BaTiO₃) over a broad frequency range. The analyzed 3D structures included a fully filled plate (PL), a basic honeycomb (BH), a honeycomb with re-entrant auxetic features (HREA), and a hierarchical honeycomb (HH). It was found that the composite material containing 1.8 wt.% CNTs and 20 wt.% BaTiO₃ exhibits the highest absorption coefficient in the frequency range from 25 GHz to 53 GHz for all investigated 3D structures. A high concentration of BaTiO₃ increases dielectric loss and interfacial polarization, while providing a CNT network. The synergy of these mechanisms results in the highest absorption of EM waves in the 25–53 GHz range. Moreover, all samples containing BaTiO₃ inclusions exhibited a distinctive electrical conductivity behavior, attributed to the high complex dielectric permittivity of barium titanate, which enhances interfacial polarization. The highest conductivity and dielectric permittivity values were measured in samples containing 1.8 wt.% CNTs and 10 wt.% BaTiO₃, while a further increase in BaTiO₃ concentration caused a decline in dielectric performance. This effect is due to the dispersion and agglomeration of filler particles in composites with higher BaTiO₃ concentrations. Full article

The dielectric properties of cement-based composites (CBC) are highly sensitive to environmental humidity, which seriously restricts the quantitative interpretation accuracy of ground-penetrating radar (GPR) in the non-destructive testing of cement concrete pavement. In view of the lack of targeted prediction models due to the unclear mechanism of humidity influence in existing research, the core innovations of this study are: (1) the synergistic mechanism of water vapor dipole polarization and adsorbed water multi-layer polarization is clarified, revealing the intrinsic reason for the accelerated growth of permittivity in the high humidity range; (2) the constructed four-component dielectric model of “cement mortar–aggregate–water vapor–adsorbed water” achieves high-precision prediction within the range of 50~100% RH (R² > 0.94, relative error < 5%), and shows good predictive ability within the test scope of this study; (3) a GPR humidity correction protocol based on the model is proposed, which can effectively improve the accuracy of nondestructive testing of cement concrete structures. In this study, CBC samples with water–cement ratios of 0.4~0.6 were prepared using P.O 32.5/P.O 42.5 cement and limestone aggregate. Under the conditions of 20 ± 0.5 °C, relative humidity (RH) of 50~100%, and 2 GHz (common GPR frequency), the permittivity was measured using an Agilent P5001A network analyzer to verify the model. The results show that the permittivity increases monotonically with humidity, and the growth rate in the high humidity range (70~100%) is 2.2 times that of the low humidity range (50~70%); The higher the water–cement ratio, the shorter the age, and the lower the cement strength grade, the stronger the humidity sensitivity of CBC dielectric properties. This model provides a reliable humidity correction tool for GPR detection, and significantly improves the accuracy of nondestructive evaluation of cement concrete structures. Full article

The present study proposes a fractal-inspired multiscale framework to interpret the structural, thermal, mechanical and dielectric properties of polylactic acid (PLA). Experimental investigations were performed using tensile testing, TG-DTA thermal analysis, X-ray diffraction (XRD) and dielectric spectroscopy. The structural organization was analyzed using XRD data, where a scaling tendency compatible with power-law behavior was identified over a limited $\mathrm{q}$-range. The thermal degradation exhibited a sharp transition, while the mechanical and dielectric responses reflected the heterogenous behavior typical of semicrystalline polymers. Rather than claiming a fully validated fractal model, the present work introduces a conceptual multiscale interpretation, supported by experimental observations, and proposes a fractal integrity index (FII) as an exploratory descriptor integrating structural, thermal and mechanical information. The results suggest that fractal-based descriptors may provide a useful complementary framework for interpreting complex polymer behavior, although further validation across multiple materials and experimental conditions is required. Full article

In battery systems, external mechanical compression is commonly applied to pouch/prismatic cells to improve their electrical performance and mechanical integrity. However, cell clamping can hinder system heat rejection by introducing an additional thermal insulation layer. A novel battery clamping scheme was designed with reduced contact area to explore the system thermal behaviour under different cooling regimes. Experimental data obtained from battery characterisation and performance tests is analysed with a thermal-coupled equivalent circuit model to quantify changes in cell impedance and system thermal properties. By reducing the clamping area by 70%, the temperature rise of the cell was decreased by 0.5 °C in comparison to the reference condition of a cell with no clamping during a 1C discharge under natural convection. Under immersion cooling using BOT2100 dielectric liquid, the thermal benefit was amplified, resulting in temperature reductions of 0.9 °C at 1C and 4 °C at 3C. The principal conclusion of this work is that reshaping the clamping plate has the potential to reduce ohmic heating by lowering battery internal resistance, which outweighs the additional thermal resistance introduced by partial surface coverage. This novel experimental approach demonstrates the potential to improve battery thermal management through geometry-optimised cell clamping, particularly for high-power applications, and further directs the community towards cell clamping solution designed to optimise both thermal and mechanical cell performance. Full article