Search Results (129)

The Clausius–Mossotti (CM) factor underpins the theoretical description of dielectrophoresis (DEP) and is widely used in micro- and nano-scale systems for frequency-dependent particle and cell manipulation. It has further been proposed as an “electrophysiology Rosetta Stone” capable of linking DEP spectra to intrinsic cellular electrical properties. In this paper, the mathematical foundations and interpretive limits of this proposal are critically examined. By analyzing contrast factors derived from Laplace’s equation across multiple physical domains, it is shown that the CM functional form is a universal consequence of geometry, material contrast, and boundary conditions in linear Laplacian fields, rather than a feature unique to biological systems. Key modelling assumptions relevant to DEP are reassessed. Deviations from spherical symmetry lead naturally to tensorial contrast factors through geometry-dependent depolarisation coefficients. Complex, frequency-dependent CM factors and associated relaxation times are shown to inevitably arise from the coexistence of dissipative and storage mechanisms under time-varying forcing, independent of particle composition. Membrane surface charge influences DEP response through modified interfacial boundary conditions and effective transport parameters, rather than by introducing an independent driving mechanism. These results indicate that DEP spectra primarily reflect boundary-controlled field–particle coupling. From an inverse-problem perspective, this places fundamental constraints on parameter identifiability in DEP-based characterization. The CM factor remains a powerful and general modelling tool for micromachines and microfluidic systems, but its interpretive scope must be understood within the limits imposed by Laplacian field theory. Full article

The compounds LiCo_1−xMn_xO₂ (x = 0.5, 0.7) were synthesized via the solid-state method and exhibited crystallization in the cubic spinel structure (space group Fd-3m). UV–Vis spectroscopy reveals strong visible-light absorption and a reduction in the indirect optical band gap from 1.85 eV (x = 0.5) to 1.60 eV (x = 0.7) with increasing Mn content, which is consistent with semiconducting behavior. This narrowing arises from Mn³⁺/Mn⁴⁺ mixed valence, which introduces mid-gap states and enhances Co/Mn 3d–O 2p orbital hybridization within the spinel framework. In contrast, the Urbach energy increases from 0.55 eV to 0.65 eV, indicating greater structural and energetic disorder in the Mn-rich composition which is attributed to the Jahn–Teller distortions and valence heterogeneity associated with Mn³⁺. Impedance and dielectric modulus analyses confirm two distinct non-Debye relaxation processes related to grains and grain boundaries. AC conductivity is governed by the Correlated Barrier Hopping (CBH) model, with bipolaron hopping identified as the dominant conduction mechanism. The x = 0.7 sample displays significantly enhanced conductivity due to increased Mn³⁺/Mn⁴⁺ mixed valence, lattice expansion, efficient 3D electronic connectivity of the spinel lattice, and reduced interfacial resistance. These findings highlight the potential of these two spinels compounds as narrow-gap semiconductors for optoelectronic applications including visible-light photodetectors, photocatalysts, and solar absorber layers extending their utility beyond conventional battery cathodes. Full article

The surface morphology of lithium metal electrodes evolves markedly during cycling, modulating interfacial kinetics and increasing the risk of dendrite-driven internal short circuits. Here, we infer this morphological evolution from direct-current (DC) signals by analyzing open-circuit voltage (OCV) transients after constant current interruptions. The OCV exhibits a rapid initial decay followed by a transition to a slower long-time decay. With repeated plating, this transition shifts to earlier times, thereby increasing the contribution of long-term relaxation. We quantitatively analyze this behavior using an equivalent circuit with a transmission-line model (TLM) representing the electrolyte-accessible interfacial region of the electrode, discretized into ten depth-direction segments. Tracking segment-wise changes in resistances and capacitances with cycling enables morphology estimation. Repeated plating strongly increases the double-layer area near the current collector, while the charge-transfer-active surface shifts toward the separator side, showing progressively smaller and eventually negative changes toward the current-collector side. Together with the segment-resolved time constants, these trends indicate that lithium deposition becomes increasingly localized near the separator-facing surface, while the interior becomes more tortuous, consistent with post-mortem observations. Overall, the results demonstrate that DC voltage-relaxation analysis combined with a TLM framework provides a practical route to track lithium metal electrode surface evolution in Li-metal-based cells. Full article

Conventional polymer-based plugging materials often fail in deep-well environments due to passive thermal softening and network relaxation, which significantly compromise mechanical integrity and interfacial retention. To address this challenge, a novel smart Upper Critical Solution Temperature (UCST)-responsive hybrid microgel (SUPA) was synthesized for adaptive plugging in complex formations. The distinctive UCST responsiveness was conferred by incorporating N-(2-amino-2-oxoethyl)acrylamide (NAGA) and N-(2-hydroxypropyl) methacrylamide (HPMA) functional units into a robust dual-crosslinked network. Particle size analysis and oscillatory rheology in saline solution revealed the thermal activation mechanism: surpassing the critical temperature triggers the dissociation of intramolecular hydrogen bonds, driving polymer chain extension and volumetric expansion. This conformational transition induces dynamic network reinforcement, quantified by a significant ~7.5-fold increase in the storage modulus (G′). Consequently, the SUPA-enhanced fluid exhibited superior rheological performance, including a 4.4-fold increase in low-shear viscosity and rapid thixotropic recovery (ratio of 1.06). Crucially, lost circulation tests confirmed reliable and highly efficient sealing performance under harsh conditions of 150 °C and 5 MPa, even in fractured models. This study validates a design strategy centered on UCST-activated network reinforcement, offering a robust, mechanism-driven solution for severe lost circulation control in deep-well drilling. Full article

Intrusive phase-detection probes remain a standard tool for local characterization of gas–liquid bubbly flows, but their accuracy is strongly affected by probe geometry and bubble–probe interaction kinematics. This work presents a Monte Carlo-based framework to evaluate four-sensor intrusive probes in bubbly flow, relaxing the classical assumptions of spherical bubbles and purely axial trajectories. Bubbles are represented as spheres or ellipsoids, a broad range of non-dimensional probe geometries are explored, and local quantities such as interfacial area concentration, bubble and flux velocities, and chord lengths are recovered from synthetic four-sensor signals. The purpose of the framework is threefold: (i) it treats four-sensor probes in a unified way for interfacial area, velocity, and chord length estimation; (ii) it includes ellipsoidal bubbles and statistically distributed incidence angles; and (iii) it yields compact correction laws and design maps expressed in terms of the spacing-to-diameter ratio $a_p/D$, the dimensionless probe radius $r_p/D$, and the missing ratio $m_r$ (defined as the fraction of bubbles that cross the probe footprint without being detected), which can be applied to different intrusive four-sensor probes. The numerical results show that, within a recommended geometric range $0.5\le a_p/D\le 2$ and $r_p/D\le 0.25$ and for missing ratios $m_r\le 0.7$, the axial velocity $V_z$ estimates the bubble centroid velocity and its projection with typical errors within $\pm 10\%$, while a chord length correction $C{L}_{corr}\left(m_r\right)$ recovers the underlying chord length distribution with a residual bias of only a few percent. The proposed interfacial area correction, written solely in terms of $m_r$, remains accurate in polydisperse bubbly flows. Outside the recommended $(a_p/D,r_p/D)$ range, large probe radius or extreme tip spacing lead to velocity and chord length errors that can exceed 20–30%. Overall, the framework provides quantitative guidelines for designing and using four-sensor intrusive probes in bubbly flows and for interpreting their measurements through geometry-aware correction factors. Full article

Improving the interfacial stability of graphite anodes remains a major challenge for extending the lifetime of lithium-ion batteries. In this study, ultrananocrystalline diamond (UNCD) and nitrogen-incorporated UNCD (N-UNCD) coatings were employed as protective layers to enhance the electrochemical and mechanical robustness of graphite electrodes. Half-cells were cycled for 60 charge–discharge cycles, and their behavior was examined through electrochemical impedance spectroscopy (EIS), Distribution of Relaxation Times (DRT), and Equivalent Circuit Modeling (ECM) to disentangle the characteristic relaxation processes. The potential–capacity profiles exhibited the typical LiC₁₂–LiC₆ transition plateaus without any additional features for the coated electrodes, confirming that the UNCD and N-UNCD films do not participate in lithium storage but serve as chemically inert and electrically stable interlayers. In contrast, the uncoated reference graphite anodes showed greater capacity fluctuations and increasing interfacial impedance. DRT and ECM analyses revealed four consistent relaxation processes—electronic transport (τ₁), ionic transport through the electrolyte (τ₂), Solid Electrolyte Interface (SEI) response (τ₃), and lithium intercalation (τ₄). The τ₂ process remained invariant, whereas τ₃ and τ₄ were markedly stabilized by the UNCD and N-UNCD coatings. UNCD exhibited the lowest SEI-related resistance and the most stable charge-transfer kinetics, while N-UNCD displayed an initially higher τ₃ resistance followed by progressive self-stabilization after 20 charge/discharge cycles, linked to reorganization of nitrogen-rich grain boundaries. Overall, polycrystalline diamond coatings—particularly UNCD—proved to be highly effective in suppressing SEI layer growth, minimizing impedance rise, and preserving lithium intercalation efficiency, leading to enhanced long-term electrochemical performance. These findings highlight the potential of diamond-based protective layers as a durable and scalable strategy for next-generation graphite anodes. Full article

This work investigates the role of preload pressure in governing the electro-chemo-mechanical (ECM) behavior of lithium iron phosphate (LFP)/graphite pouch cells during calendar aging. Cells aged at 60 °C under different preload levels were systematically evaluated through in situ monitoring of force evolution and capacity retention. To interpret these behaviors, a coupled model was developed that integrates solid electrolyte interphase (SEI)-induced electrode expansion, viscoelastic relaxation, and stiffness evolution, and it was validated against multi-rate discharge experiments, showing excellent agreement with measured voltage and force responses. The results reveal that higher preload amplifies internal pressure fluctuations, prolongs viscoelastic relaxation, and delays irreversible force recovery, while the overall capacity fade remains largely unaffected. A slight mitigation in capacity loss is observed at high preload, primarily due to suppressed SEI growth resulting from reduced electrode porosity and a decrease in active surface area available for interfacial reactions. Fitting parameters for stiffness correction, relaxation amplitude, and relaxation time exhibited systematic preload dependence. By decoupling irreversible and relaxation forces, the framework enables quantitative analysis of aging-induced pressure accumulation. Overall, this study underscores the critical role of mechanical constraints in long-term battery degradation and demonstrates the predictive capability of the proposed ECM model for guiding preload design in practical modules. Full article

The performance of heterogeneous polymer-based materials is largely governed by the efficiency of interfacial adhesion and the strength of interactions between their constituent phases. This work mainly focuses on correlating the properties of dielectrically active interfaces, identified through broadband dielectric spectroscopy (BDS), with the mechanical behavior of heterogeneous polymer-based materials. Blends of polypropylene (PP) and biodegradable poly (butylene succinate) (PBS) were investigated across a wide composition range (100/0, 80/20, 70/30, 50/50, 20/80, and 0/100 PP/PBS). The interface between the immiscible PP and PBS phases induces a Maxwell–Wagner–Sillars (MWS) interfacial polarization in the permittivity spectrum. For the 80PP/20PBS formulation, the high activation energy of this polarization is well correlated with the material’s elevated tensile strength measured under uniaxial tension. A series of nanocomposites based on the 80PP/20PBS blend and reinforced with organically modified montmorillonite (Cloisite 20A) were thoroughly investigated. A strong correlation was established between their mechanical performance and the additional interfacial polarization arising from charge accumulation at the clay–matrix interface. The 80PP*/20PBS–3%C20 nanocomposite demonstrated superior matrix–filler adhesion, reflected by the highest activation energy of interfacial polarization and a marked increase in Young’s modulus (~22%) and zero-shear viscosity η₀ (~44%). Complementary rheological measurements confirmed a substantial increase in viscosity and relaxation time for the 80PP/20PBS–3%C20 nanocomposites, indicating restricted chain mobility and the formation of a percolated network. Morphological analysis by SEM provided insights into the overall microstructure of the polymer blends and nanocomposites. These results demonstrate a direct correlation between interfacial structure, chain dynamics, and macroscopic performance in immiscible polymer blends and nanocomposites. Full article

This study investigated the effect of nanofiller on the structural properties of thermally aged polyvinyl chloride (PVC)/Aluminum oxide (Al₂O₃) nanocomposites prepared with different amounts of nanoparticles (2.5, 5.0, and 7.5 wt%) using various techniques. Experimental studies were designed to monitor structural changes in PVC/Al₂O₃ nanocomposites by means of dielectric characterization, charging and discharging currents measurements, SEM and FTIR analyses, and visual observations as a function of nanofiller amount and aging time. The results obtained demonstrated that the dielectric permittivity of PVC was increased for unaged samples with the addition of 2.5% and 7.5% Al₂O₃ nanoparticles. An increase in dielectric losses is also observed at the same level of filler content, attributable to interfacial polarization driven by improved charge transport and dipole relaxation. A decrease in charging and discharging currents with higher Al₂O₃ content is attributed to an increase in matrix rigidity, which restricts charge carrier mobility. The charging and discharging currents progressively increased during thermal aging, as polar aging products were formed during this process, which could improve charge mobility and conductivity. FTIR and SEM analyses indicated that with thermal aging, polar groups formation was more likely due to structural decomposition of the matrix and mild dehydrochlorination. The changes in color were indicative of surface degradation. These results provide new insight into the electrical and aging behaviors in PVC/Al₂O₃ nanocomposites. Full article

Electrocatalytic water splitting offers a promising route to sustainable H₂, but the oxygen evolution reaction (OER) in alkaline media remains the principal bottleneck for activity and durability. This review focuses on alkaline OER and integrates mechanism, kinetics, materials design, and cell-level considerations. Reaction mechanisms are outlined, including the adsorbate evolution mechanism (AEM) and the lattice oxygen mediated mechanism (LOM), together with universal scaling constraints and operando reconstruction of precatalysts into active oxyhydroxides. Strategies for electronic tuning, defect creation, and heterointerface design are linked to measurable kinetics, including iR-corrected overpotential, Tafel slope, charge transfer resistance, and electrochemically active surface area (ECSA). Representative catalyst families are critically evaluated, covering Ir and Ru oxides, Ni-, Fe-, and Co-based compounds, carbon-based materials, and heterostructure systems. Electrolyte engineering is discussed, including control of Fe impurities and cation and anion effects, and gas management at current densities of 100–500 mA·cm⁻² and higher. Finally, we outline challenges and directions that include operando discrimination between mechanisms and possible crossover between AEM and LOM, strategies to relax scaling relations using dual sites and interfacial water control, and constant potential modeling with explicit solvation and electric fields to enable efficient, scalable alkaline electrolyzers. Full article

The Ni/Al₂O₃ interface bears the load transfer and energy dissipation, which determines the service performance of the composite materials. In this study, three distinct vacancy-defect-modified interface models (D₁, D₂, and D₃, corresponding to vacancies in the first, second, and third layers of the Ni substrate surface, respectively) were constructed to systematically investigate the regulatory mechanism of vacancies on interfacial stability. The underlying mechanism of vacancy-enhanced interfacial stability was elucidated from both atomic-scale structural and electronic property perspectives. The results demonstrate that the D₁, D₂, and D₃ structures increase the adhesion work of the interface by 2.0%, 6.7%, and 0.3%, respectively. This enhancement effect mainly stems from vacancy-induced atomic relaxation at the interface, which optimizes the equilibrium interfacial spacing and effectively releases residual strain energy. Further electronic structure analysis reveals a notable increase in charge density at the vacancy-modified interface (particularly in the D₂ structure), indicating that vacancy defects promote charge transfer and redistribution by altering local electron distribution. More importantly, the bonding strength of the interface exhibits a positive correlation with electron orbital hybridization intensity, where stronger s-, p-, and d-orbit hybridization directly leads to a more stable interface. These findings provide atomic- and electronic-scale insights into the mechanistic role of vacancy defects in governing bonding at the Ni/Al₂O₃ interface. Full article

This study reports the synthesis, structural characterization, and electromagnetic shielding performance of tantalum (Ta)-doped nickel ferrite (NiFe₂O₄) composites reinforced with chopped strands. Ta-doped NiFe₂O₄ powders were prepared via the conventional mixed-oxide route and sintered at 1200 °C for 4 h, resulting in a well-crystallized single-phase spinel structure. Comprehensive structural and chemical analyses were carried out using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS), confirming the successful incorporation of Ta into the NiFe₂O₄ lattice and the uniform microstructural distribution. The ferrite powders were subsequently embedded with chopped strands and epoxy resin through hot pressing to fabricate composites with varying filler contents. The electromagnetic interference (EMI) shielding effectiveness (SE) of the composites was systematically evaluated in the 7–18 GHz frequency range using a network analyzer (NA). The optimized composite, with a thickness of 1.2 mm, demonstrated a maximum SE of 34.74 dB at 17.4 GHz, primarily attributed to interfacial polarization, dipolar relaxation, and multiple scattering effects induced by the chopped strands. The results indicate that the shielding performance of the composites can be precisely tuned by modifying the filler concentration and microstructural characteristics, enabling selective frequency-band applications. Overall, this work highlights the potential of Ta-doped NiFe₂O₄/chopped strand composites as lightweight, cost-effective, and high-performance candidates for advanced microwave absorption and electromagnetic shielding applications in defense, and next-generation communication technologies. Full article

Chitosan films obtained by solution casting were investigated by broadband dielectric spectroscopy (BDS) to explore both their glass transition and the effects of thermal annealing on molecular dynamics, deriving from residual water content as well as from cold crystallization. Glass transition at low temperatures could be evidenced in as-produced as well as thermally annealed films, where non-Arrhenian dielectric relaxation processes, consistent with a structural (α) relaxation, could be detected. The process detected at low temperatures could reflect the dynamics of residual water slaved by the polymer matrix. Secondary (β) relaxations, along with a slow process ascribed to interfacial polarization at the amorphous/crystalline interfaces, were concurrently detected. In most cases, a further Arrhenian process at intermediate temperatures (α_c) was present, also indicative of crystallization. Notably, the α processes, due to the primary relaxation of the polymer matrix plasticized by water, could be discriminated from other processes, present in the same frequency range, thanks to improvements in the dielectric fitting strategy. All relaxation processes showed the expected dependence on T_a. The more accurate exploration of the glass transition for chitosan helps to better rationalize its crystallization behavior, in view of an optimized application of this biopolymer. Full article

Here, the effects of Fe vacancy defects on the bonding properties of γ-Fe (111)/α-Al₂O₃ (0001) interfaces are studied in depth at the atomic and electronic levels using first-principles calculations. The first (V₁), second (V₂), third (V₃), and fourth (V₄) layers of vacancy structures within the Fe substrate, as well as the ideal Fe/Al₂O₃ interface structure, are proposed and contrasted, including their thermodynamic parameters and atomic/electronic properties. The results demonstrate that the presence of vacancies in the first atomic layer of Fe deteriorates the interfacial bonding strength, whereas vacancies situated in the third layer enhance the interfacial bonding strength. The effect of vacancy beyond the third layer becomes negligible. This occurs mainly because vacancy defects at different positions induce the relaxation behavior of atoms, resulting in bond-breaking and bond-forming reactions at the interface. Following that, the formation process of vacancies can cause the transfer and rearrangement of the electrons at the interface. This process leads to significant changes in the charge concentration of the interfaces, where V₃ is the largest and V₁ is the smallest, indicating that the greater the charge concentration, the stronger the bonding strength of the interface. Furthermore, it is discovered that vacancy defects can induce new electronic orbital hybridization between Fe and O at the interface, which is the fundamental reason for changes in the properties of the interface. Interestingly, it is also found that more electronic orbital hybridization will strengthen the bonding performance of the interface. It seems, then, that the existence of vacancy defects not only changes the electronic environment of the Fe/Al₂O₃ interface but also directly affects the bonding properties of the interface. Full article

Unidirectional carbon fiber-reinforced polymer (UD-CFRP) composites demonstrate superior tensile creep strain and stress relaxation behavior along fiber orientation. However, prolonged transverse compressive loading in structural connection zones induces significant interfacial stress relaxation and creep deformation, primarily driven by resin matrix degradation and interfacial slippage under thermal-mechanical interactions, and remains poorly understood. This study systematically investigates the transverse stress relaxation characteristics of UD-CFRP through controlled experiments under varying thermal conditions (20–80 °C) and compressive stress levels (30–80% ultimate strength). Post-relaxation mechanical properties were quantitatively evaluated, followed by the development of a temperature-stress-time-dependent predictive model aligned with industry standards. The experimental results reveal bi-stage relaxation behavior under elevated temperatures and compressive stresses, characterized by a rapid primary phase and stabilized secondary phase progression. Notably, residual transverse compressive strength remained almost unchanged, while post-relaxation elastic modulus increased by around 10% compared to baseline specimens. Predictive modeling indicates that million-hour relaxation rates escalate with temperature elevation, reaching 51% at 60 °C/60% stress level—about 1.8 times higher than equivalent 20 °C conditions. These findings provide crucial design insights and predictive tools for ensuring the long-term integrity of CFRP-based structures subjected to transverse compression in various thermal environments. Full article