Local Diffusion Research Articles

On the effect of localized large diffusion in one-dimensional semilinear thermoelastic systems

In this work we introduce a one-dimensional semilinear system arising from the effect of localized large diffusion in one-dimensional semilinear thermoelastic systems. We prove the existence of the global attractor for this new system, as well as, we also prove that each positive orbit of this new system converges to a single equilibrium point.

Diagnostic Investigation of Two EDMF Planetary Boundary Layer Schemes Used in the GFS Model

Abstract The behavior of two eddy-diffusivity mass-flux (EDMF) planetary boundary layer schemes used in versions 15 and 16 of NOAA’s operational Global Forecast System (GFS) is examined in terms of local and nonlocal mixing processes in a one-dimensional (1D) model configuration. Diagnosis using process perturbation sensitivity experiments indicates that the nonlocal mixing represented by the mass-flux term is much more dominant in one scheme than the other. Quantitative aspects of the local eddy diffusivity are different between the two schemes, pointing to uncertainty in the physical partition of local and nonlocal mixing in the EDMF formulation. One of the two schemes is also shown to produce unphysical thermal and tracer tendencies due to the scheme’s specific numerical treatment of moist nonlocal mixing. To resolve this problem, a physically and numerically consistent approach is proposed to calculate these tendencies.

Photodegradable polyacrylamide tanglemers enable spatiotemporal control over chain lengthening in high-strength and low-hysteresis hydrogels.

Covalent hydrogel networks suffer from a stiffness-toughness conflict, where increased crosslinking density enhances the modulus of the material but also leads to embrittlement and diminished extensibility. Recently, strategies have been developed to form highly entangled hydrogels, colloquially referred to as tanglemers, by optimizing polymerization conditions to maximize the density and length of polymer chains and minimize the crosslinker concentration. It is challenging to assess entanglements in crosslinked networks beyond approximating their theoretical contribution to mechanical properties; thus, in this work, we synthesize and characterize polyacrylamide tanglemers using a photolabile crosslinker, which allows for direct assessment of covalent trapping of entanglements under tension. Further, this chemistry allows tuning of the modulus in situ by crosslink photocleavage (from tensile modulus (ET) = 100 kPa to <25 kPa). Beyond cleavage of crosslinks, we demonstrate that even non-degradable tanglemer formulations can be photo-softened and completely degraded through Fe3+-mediated oxidation of the polyacrylamide backbone. While both photodegradation methods are useful for spatial patterning and result in softer gels with reduced fracture strength, only crosslink photocleavage improves gel extensibility via light-induced chain lengthening (εF = 700% to >1500%). Crosslink photocleavage in tanglemers also affords significant control over localized swelling and diffusivity. In sum, we introduce a simple and user-directed approach for probing entanglements and asserting spatiotemporal control over stress-strain responses and small molecule diffusivity in polyacrylamide tanglemers, suggesting a multitude of potential soft matter applications including controlled release and tunable bioadhesive interfaces.

МЕТОДОЛОГИЧЕСКИЕ ОСНОВЫ МАТЕРИАЛОВЕДЧЕСКОЙ ОЦЕНКИ КАЧЕСТВА СМАЗОЧНЫХ СРЕД ДЛЯ НАГРУЖЕННЫХ СОПРЯЖЕНИЙ МАШИН И МЕХАНИЗМОВ. Сообщение 2. Влияние состава смазочных сред на структурно-фазовое состояние зоны деформации металлических трибосопряжений и их антифрикционные свойства

The results of experimental studies of deformation and diffusion in the surface layers of metallic frictional couples, which form the experimental and theoretical basis of the materials science approach to the quality evaluation of lubricants, are presented. The concepts of the component’s role for the lubricating medium in the implementation of the plasticizing and strengthening triboeffect are formulated. Structural condition characteristics for the surface layers of copper alloys during friction on steel in the mode of boundary lubrication in surface-active lubricants, are described. The conditions for achieving minimum power losses of such tribosystems for friction and wear have been found. The greatest service life of tribounit in a lubricating medium containing surfactants is resulted from wear resistance increase of a copper alloy with a relative decrease in hardness and increased plasticity of its surface layer. At the same time, a decrease in hardness due to the plasticizing effect of surfactants occurs only in the near-surface deformed layer of tribomaterial, while in its deeper layers with no plasticization resulted from a lubricating medium effect, the mechanical characteristics of the antifriction alloy remain at the required high level. It is demonstrated that alloys with a single-phase structure of an α-solid solution and a wide concentration range of solubility of the alloying element in the solid state meet these requirements. It is found that such boundary conditions are provided by the presence of stationary macroscopic diffusion flows of alloying elements in the zone of contact deformation of a polycomponent tribomaterial. The role of local diffusion phenomena in quasispinodal phase transitions is indicated. Examples of the selective transfer phenomenon during friction in industrial lubricants, are given.

Preserving large-scale features in simulations of elastic turbulence

Simulations of elastic turbulence, the chaotic flow of highly elastic and inertialess polymer solutions, are plagued by numerical difficulties: the chaotically advected polymer conformation tensor develops extremely large gradients and can lose its positive-definiteness, which triggers numerical instabilities. While efforts to tackle these issues have produced a plethora of specialized techniques – tensor decompositions, artificial diffusion, and shock-capturing advection schemes – we still lack an unambiguous route to accurate and efficient simulations. In this work, we show that even when a simulation is numerically stable, maintaining positive-definiteness and displaying the expected chaotic fluctuations, it can still suffer from errors significant enough to distort the large-scale dynamics and flow structures. We focus on two-dimensional simulations of the Oldroyd-B and FENE-P equations, driven by a large-scale cellular body forcing. We first compare two positivity-preserving decompositions of the conformation tensor: symmetric square root (SSR) and Cholesky with a logarithmic transformation (Cholesky-log). While both simulations yield chaotic flows, only the latter preserves the pattern of the forcing, i.e. its fluctuating vortical cells remain ordered in a lattice. In contrast, the SSR simulation exhibits distorted vortical cells that shrink, expand and reorient constantly. To identify the accurate simulation, we appeal to a hitherto overlooked mathematical bound on the determinant of the conformation tensor, which unequivocally rejects the SSR simulation. Importantly, the accuracy of the Cholesky-log simulation is shown to arise from the logarithmic transformation. We also consider local artificial diffusion, a potential low-cost alternative to high-order advection schemes. Unfortunately, the artificially enhanced diffusive smearing of polymer stress in regions of intense stretching substantially modifies the global dynamics. We then show how the spurious large-scale motions, identified here, contaminate predictions of scalar mixing. Finally, we discuss the effects of spatial resolution, which controls the steepness of gradients in a non-diffusive simulation.

Quaternary Electrolyte Mixtures for Rechargeable Aluminum-Sulfur Batteries

Rechargeable aluminum-sulfur (Al-S) batteries hold great potential due to the abundance, safety, low cost, and high gravimetric capacity of Al metal and elemental sulfur (2980 mAh g-1 and 1675 mAh g-1, respectively). Despite these advantages, technological development of Al-S batteries faces challenges due to the limited number of electrolytes that not only enable the reversible electrostripping of Al metal and concomitant electroreduction of sulfur, but also yield small polarization losses. Currently, Lewis acidic mixtures of AlCl3 in 1-ethyl-3-methylimidazolium chloride ([EMIm]Cl) are the state-of-the-art electrolytes used in Al metal batteries, including Al-S batteries, though polarization losses in Al-S cells are large at room temperature. Recently, alkali chloroaluminate molten salts (NaCl-KCl-AlCl3) were tested in Al-S batteries at 110 °C, resulting in a large decrease in polarization compared to AlCl3-[EMIm]Cl electrolytes, even at elevated temperatures [1]. However, the link between chloroaluminate anion speciation and dynamics, temperature, and overpotential for sulfur reduction and oxidation is poorly understood.Here, we prepare quaternary electrolyte mixtures composed of AlCl3, NaCl, KCl, and either [EMIm]Cl, urea, or LiCl to reduce the liquid temperature window and study how ion speciation and dynamics affect polarization losses in rechargeable Al-S batteries as a function of temperature. All mixtures were compared to AlCl3-[EMIm]Cl (1.5:1 molar ratio) and NaCl-KCl-AlCl3 (26:13:61) molar ratio mixtures as baseline electrolytes. Differential scanning calorimetry (DSC) was performed to measure thermodynamic phase transitions and the liquid temperature windows of these electrolytes. Liquid-state 27Al single-pulse and relaxation nuclear magnetic resonance (NMR) measurements were performed to characterize chloroaluminate anion speciation environments, and dynamics up to 110 °C. In addition, liquid-state 1H single-pulse, relaxation, and pulsed-field-gradient (PFG) NMR experiments were performed to measure the local environments, dynamics, and diffusion coefficients of organic species (e.g., [EMIm]Cl, urea).The electrolytes were tested electrochemically in rechargeable Al-S batteries by performing galvanostatic cycling and cyclic voltammetry up to 110 °C, revealing the effects on cell polarization as well as specific capacity and cyclability. Furthermore, solid-state 27Al NMR measurements on discharged sulfur electrodes containing residual electrolyte [2] revealed how electrolyte composition affects the average environments of rapidly exchanging electrolyte-soluble sulfur species (SxAlCl4)y−). Overall, the results yield design strategies for electrolyte design in rechargeable Al-S batteries to reduce the operating temperature, reduce the polarization loss, and enhance energy efficiency. References “Fast-Charging Aluminium–Chalcogen Batteries Resistant to Dendritic Shorting.,” Quanquan Pang, Jiashen Meng, Saransh Gupta, Xufeng Hong, Chun Yeun Kwok, Ji Zhao, Yingxia Jin, Like Xu, Ozlem Karahan, Ziqi Wang, Spencer Toll, Liqiang Mai, Linda Nazar, Mahalingam Balasubramanian, Badri Narayanan, Donald Sadoway, Nature., 2022, 608, 704-711.“Soluble electrolyte-coordinated sulfide species revealed in Al-S Batteries by nuclear magnetic resonance spectroscopy,” Rahul Jay, Ankur L. Jadhav, Leo W. Gordon, Robert J. Messinger, Chem. Mater., 2022, 34, 4486-4495.

Electric field-controlled on-demand surface deformation in liquid crystal polymer networks with topological defects

ABSTRACT Reconfigurable surface morphing control of liquid crystalline polymer (LCP) films at micro or nano scales has emerged as a promising strategy for various applications. Creating reproducible and adjustable platforms enhances their versatility. This study presents a method for controlling stimuli-responsive deformations in liquid crystal polymer network (LCN) films by forming defect arrays using a three-dimensional (3D) electric field generated by crossed electrode systems. The director field of the system can be simulated, enabling investigation of high-temperature deformations through activation force density calculations. To explain the laterally asymmetric deformation of our film, a 3D analysis of the activation force density vector field was essential. Topographical modifications at room temperature are also achieved by incorporating dichroic dye to the monomeric mixture, which promote local monomer diffusion during photopolymerisation. Additionally, by varying the configurations of signal and ground electrodes, different defect structures are generated, leading to distinct deformation patterns at elevated temperatures. Our findings demonstrate that LCN films in this study exhibit programmable nanometre-scale shape deformations, allowing for varied surface patterns from a single setup. This platform significantly enhances the potential of nano- or micro-morphing LCP coatings for advanced applications across multiple fields.

Modulating the Electrochemical Potential and Zn2+ Diffusion Kinetics in Hydrated Vanadate

Hydrated vanadate (V2O5·nH2O) is regarded as one of the promising cathodes for aqueous zinc ion batteries owing to their high specific capacity and low cost, however, their relatively low operating voltage and sluggish kinetics limit their practical applications. Compared to preinserted metal cations, we develop a series of organic cations, with similar molecular structure but distinct functional terminal-groups, are pre-intercalated into the lattice of hydrated vanadate to regulate the local chemical coordination and the electronic structure of the redox cation. The stronger polarity or larger size causes larger local distortion of VO6 octahedron and V t 2g orbitals splitting, leading to a higher open circuit voltage (>1.60 V) and higher mid-point voltage (>0.75 V) in comparison with unmodified sample. In addition, the modified samples present higher ion diffusion coefficient of 10-8~-7 cm2/s compared with 10-9~-8 cm2/s, resulting in a better rate performance. The understanding on the correlation among local chemical coordination, electrochemical potentials, and ion diffusion could serves as a guide for designing and developing higher energy and power densities in next generation rechargeable batteries.

Cavity self-healing mechanism at the interface of high-Cr ferritic steel/austenitic steel dissimilar diffusion-bonded joint during cyclic phase transformation treatment

In this work, cyclic phase transformation treatment (CPTT) was developed to achieve self-healing of interfacial voids in high-Cr ferritic steel/austenitic steel dissimilar diffusion-bonded joints. The evolution of voids was analyzed based on microstructural characteristics, and mechanical properties of joints were assessed through lap-shear tensile tests. The results indicate that, in contrast to isothermal heat treatment (IHT), CPTT significantly enhances efficiency of cavity healing, leading to substantial improvements in both interface bonded ratio and shear performance of joints. By considering equivalent interfacial internal stress, a kinetic model for cavity healing was proposed, incorporating coupled the interface and surface diffusion, and the power-law creep mechanism. Simulation results demonstrate that diffusion predominates during cavity healing with negligible contribution of plastic flow. The actual cavity healing can be divided into two stages: in initial stage the large penny-shaped cavities become shorter in length with negligible change of height, while in the final stage, nearly circular voids shrinkage with a significant decrease of void size due to the enhanced effect of local surface diffusion. Moreover, it suggests that tensile internal stresses can impede healing or even promote residual void growth. Conversely, normal compressive internal stresses within cavity healing zone induced by the cyclic α↔γ phase transformation during CPTT intensify chemical gradients around void neck. This promotes accelerated atomic diffusion adjacent to void neck region, thereby resulting in a notable reduction in the duration required for complete cavity healing.

Influence of the Clamping Force and the Formation of Liquid Water Along the Channel on the Local Diffusion Processes in PEMFCs

The success of PEMFCs in heavy duty applications depends on achieving high power densities while maintaining exceptional durability. Under high current density operating conditions, the transport of oxygen from the gas channel via the GDL and MPL to the active Pt-particles in the catalyst layer becomes performance limiting. In the different layers, oxygen transport takes place via various transport processes, such as Knudsen, molecular and ionomer diffusion. Gas transport in a fuel cell is influenced to varying degrees by the operating conditions, geometry of the flow channel, and the properties of the porous media. Porosity and tortuosity of the diffusion media depend on the local clamping force and the amount of liquid water present. In a large-active-area cell, the clamping force and liquid water as well as oxygen concentration, pressure and temperature can vary significantly between the inlets and the exits, which results in a spatially varying oxygen transport resistance and local performance along the channel. To enable targeted optimization of the operating strategy and component design for high current density operation, a comprehensive understand of the local diffusion processes and their dependencies is essential.In our study, limiting current measurement is used as a diagnostic tool in combination with a segmented cell to determine the local oxygen transport resistance [1, 2]. In the measurement setup, the clamping force is manually set for each segment and recorded continuously throughout the experiment. By systematically varying the operating conditions (p, RH, T), clamping force and cathode gas composition (N2/He), we aim to deconvolute each transport mechanism and the allocation of the transport resistance to each individual layer. The local operating conditions, such as pressure and temperature, are simulated using empirical models based on local measurement data. The combined results allow us to obtain the local oxygen transport resistance as a function of local operating conditions and the clamping force along the flow channel.In this study, the distribution of different gas diffusion processes and their impact on fuel cell performance along the channel are presented. In particular, the effect of the clamping force and the formation of liquid water along the channel on local porosity and tortuosity in the GDL are discussed. Furthermore, our results demonstrate how the overall performance of the cell can be optimized by adjusting the clamping force distribution along the flow channel.

The Immunologic Downsides Associated with the Powerful Translation of Current COVID-19 Vaccine mRNA Can Be Overcome by Mucosal Vaccines.

The action of mRNA-based vaccines requires the expression of the antigen in cells targeted by lipid nanoparticle-mRNA complexes. When the vaccine antigen is not fully retained by the producer cells, its local and systemic diffusion can have consequences depending on both the levels of antigen expression and its biological activity. A peculiarity of mRNA-based COVID-19 vaccines is the extraordinarily high amounts of the Spike antigen expressed by the target cells. In addition, vaccine Spike can be shed and bind to ACE-2 cell receptors, thereby inducing responses of pathogenetic significance including the release of soluble factors which, in turn, can dysregulate key immunologic processes. Moreover, the circulatory immune responses triggered by the vaccine Spike is quite powerful, and can lead to effective anti-Spike antibody cross-binding, as well as to the emergence of both auto- and anti-idiotype antibodies. In this paper, the immunologic downsides of the strong efficiency of the translation of the mRNA associated with COVID-19 vaccines are discussed together with the arguments supporting the idea that most of them can be avoided with the advent of next-generation, mucosal COVID-19 vaccines.

Revealing the Interplay of Local Environments and Ionic Transport in Perovskite Solid Electrolytes.

Solid-state ionic conduction is significantly influenced by bottleneck sizes, which impede ion diffusion within solid lattices. Using aberration-corrected scanning transmission electron microscopy and multislice electron ptychography, we directly observed that increased La occupancy in the perovskite solid electrolyte Li0.5La0.5TiO3 correlates with reduced bottleneck sizes formed by four oxygen atoms connecting neighboring A-site cages. This correlation was also confirmed in local aperiodic regions, where smaller bottleneck sizes due to increased La occupancies affect the directionality and dimensionality of the Li+ ion conductivity. Furthermore, while prior studies have focused on averaged Li+ ion diffusion across different bottleneck areas or chemical environments, by devising a molecular dynamics (MD)-based methodology, we quantify the diffusivity of Li+ ions through specific bottleneck regions. Atomistic simulations, including nudged elastic band calculations and this MD-based methodology, revealed that larger bottleneck sizes correlate with smaller local migration barriers and higher local diffusivity. This study elucidates the relationship among local chemistry, lattice structure, and Li+ ion transport, providing insights for the design of advanced oxide solid electrolytes.

Hydrogen diffusion mechanisms in the 4130X steel: An integrated study with electrochemical experiments and molecular dynamics simulations

In this work, hydrogen diffusion behavior and mechanisms in the 4130X steel influenced by temperature, locally high concentration, and grain boundary were studied by leveraging both electrochemical hydrogen permeation experiments and molecular dynamics simulations. It was revealed that the hydrogen diffusion coefficient of the 4130X steel was increased with increasing temperature and decreasing locally high hydrogen concentration. The grain boundaries with misorientation below 15° characterized by an electron backscatter diffraction map were identified as hydrogen trapping sites, thus rendering a lower mean square displacement of hydrogen atoms and localized hydrogen diffusion trajectories. Furthermore, at a high hydrogen concentration of 4 at. %, these grain boundaries were saturated by hydrogen atoms, and platelet-like hydrogen clusters were formed within the lattice, which further inhibited the diffusive motion of hydrogen atoms. These findings would deepen our understanding of hydrogen embrittlement mechanisms by establishing the connections between macroscopic permeation behavior and atomic-scale hydrogen diffusion in structural materials.

Excellent radiation resistance via enforced local non-directional He diffusion in a WTaCrV multicomponent alloy containing coherent ordered nanoprecipitates

We design and investigate a W15Ta15Cr35V35 (at.%) multicomponent alloy (MCA) with exceptional radiation resistance. The sintered WTaCrV alloy exhibits a body-centered cubic (BCC) matrix with dispersed coherent ordered nanoprecipitates. After ∼3-hour irradiation under 400 keV He+ at room temperature (RT) and 450 °C with a fluence of 2 × 1017 ions/cm2, the irradiation hardening values of the MCA are about a quarter of those of pure tungsten counterparts irradiated at identical conditions. Besides, helium bubbles generated in the irradiated matrix of the MCA are much smaller, compared with those in the pure tungsten and other tungsten-rich alloys previously reported. The exceptional radiation resistance of the present WTaCrV alloy can be mainly attributed to two synergistic mechanisms. First, the high lattice distortion of the solid solution matrix promotes the local non-directional diffusion of irradiation defects, effectively suppressing the aggregation of irradiation defects and helium atoms along specific orientations. This facilitates more uniform nucleation of helium bubbles in the alloy matrix. Second, carbon was introduced during fast hot pressing sintering as interstitial solute to form carbon-rich coherent ordered nanoprecipitates. The carbon-vacancy complexes generated in the nanoprecipitates inhibit the nucleation and aggregation of helium atoms at the vacancies during He+ irradiation. The above two mechanisms synergistically enhance the resistance against He+ irradiation. This work thus demonstrates a design strategy for high radiation resistance alloys by introducing well-tuned ordered coherent nanoprecipitates in multicomponent alloy systems.

Study on the deep deoxidation mechanism of titanium powder using Y/YOCl/YCl3 and Y/Y2O3 systems

Low-oxygen high-purity titanium (oxygen concentration ≤ 500 ppm) is a critical material for advanced semiconductor and biomedical applications. Current deoxidation methods limit oxygen concentration in titanium to approximately 1000–2000 ppm, failing to meet the demand for ultra-low oxygen levels in high-performance materials. This study investigated the preparation mechanism and conditions for low-oxygen high-purity titanium utilizing a molten salt thermochemical method, employing Y as the deoxidant with a theoretical deoxidation limit below 10 ppm. We experimentally explored the deoxidation mechanisms of titanium using Y/YOCl/YCl3 and Y/Y2O3 systems, successfully reducing the oxygen concentration in titanium to 200 ppm, and proving that the Y/YOCl/YCl3 system is more efficient than the Y/Y2O3 system. Additionally, the titanium samples were analyzed using SEM-EDS, XRD, XPS, and 3D surface profilometry before and after deoxidation. These analyses examined the impact of the deoxidation process using Y on the crystal structure, oxide film, and surface roughness of titanium specimens, which are useful for understanding the deoxidation mechanism. During the sintering process of titanium powder attached to Y, the deoxidation process will produce YOCl or Y2O3. The formation of these deoxidation products leads to local oxygen diffusion, and the crystals of YOCl or Y2O3 are gathered at grain boundaries, which will resolve during the subsequent acid etching process, thus reducing the oxidation concentration of the titanium. The above results provide further theoretical guidance and technical support for the production of ultra-high-purity titanium powder.

DM-HAP: Diffusion model for accurate hand pose prediction

Forecasting hand poses is a challenging task due to inherent uncertainties, occlusions, and inaccuracies in 3D pose estimation. Diffusion models provide a promising direction for predicting precise 3D hand poses under noisy conditions. In this work, we introduce Dual-diffusion, an innovative framework for the precise prediction of future hand poses. Our approach leverages the strengths of diffusion models by framing hand pose forecasting as a reverse diffusion process, effectively addressing the complexities of noisy hand joint movements and their subtleties. To enhance the learning of hand pose representations, we propose a unique neural architecture that simultaneously captures both local and global features. This is achieved through the deployment of Global and Local Diffusion (GLD) blocks within our network, which facilitate the exchange of information between local and global features. This diffusion-based interaction enables the integration of global hand actions and local finger actions, leading to a more powerful representation learning approach. We evaluate the effectiveness of our Dual-diffusion method on three public 3D hand pose estimation datasets (MSRA, F-PHAB, and BigHand2.2M), and our approach outperforms previous methods.

Computational aeroacoustics of low-pressure axial fans installed in parallel

Abstract Ducted rotor-only Low-Pressure Axial (LPA) fans play an integral role in automotive thermal management of electric vehicles and are the primary source of noise from the underhood region. Multiple LPA fans are often placed in parallel in cooling packages of electric vehicles. There is little scientific work concerning aeroacoustics of ducted LPA fans operating in parallel. This work aims to address this gap through hybrid computational aeroacoustic simulations. Three-dimensional, full-annulus, transient simulations are done using the Delayed Detached Eddy Simulation (DDES) turbulence model. First, a numerical validation study is presented, where aerodynamic and aeroacoustic results from this work are compared to experimental results for a LPA fan issued by the European Acoustics Association (EAA). In the second part, aeroacoustic performance of two-fans placed in parallel is presented. A local diffusion zone is observed in the region where the two-fans are closest to one another. A previously unidentified vortex which envelopes the local diffusion zone is observed. For two-fans in parallel, the amplification of the acoustic spectrum scales in accordance to having two identical equally strong sound sources, i.e, by 6 dB. The scaling of the acoustic spectrum for two-fans in parallel in comparison to a single-fan suggests limited interaction between the acoustic field of the two-fans.

Investigation on the creep mechanism of PA6 films based on quasi point defect theory

Polyamide 6 (PA6) films with significant α relaxation process was selected as the model system. The creep behavior and rheological mechanism during deformation in the amorphous regions of semi-crystalline polymers are systematically investigated by carrying out creep experiments. Based on the quasi point defect (QPD) theory, the complete physical process of PA6 film creep behavior from elasticity to viscoelasticity and viscoplasticity was analyzed and modeled from the perspective of structural heterogeneity. The results demonstrate that the creep deformation of PA6 film is a typical thermo-mechanical coupling and nonlinear mechanics process, and potential creep mechanisms corresponds to stress-induced local shear deformation enhancement and thermal activation-induced particle flow diffusion. The elastic-plastic transition involved in the creep deformation process of semi-crystalline polymer originates from the activation of quasi-point defective sites in the amorphous region, the expansion of sheared micro-domains and irreversible fusion. The generalized fractional Kelvin (GFK) model is proposed, and the physical meaning of parameters is explained by combining the quasi point defect theory and creep delay spectrum(L(τ)). Finally, the effectiveness of the GFK model and the QPD theory in studying the deformation behavior of PA6 films was validated by comparing experimental data with theoretical results, which theoretically reveals the structural evolution of PA6 film during creep process.

Influence of the Clamping Force and the Formation of Liquid Water Along the Channel on the Local Diffusion Processes in PEMFCs

A novel measurement setup, technique, and segmented model are introduced to spatially resolve mass transport losses along the channel in a PEMFC. The newly designed segmented cell enables not only the measurement of local current and voltage data but also the capture of local temperature and compression levels. By extending the commonly used limiting current method, the local mass transport resistance is determined as a function of local operating parameters. The local current and temperature are directly measured, while the operating conditions along the channel such as pressure, oxygen fraction, and relative humidity are obtained empirically from a 1-D differential model. Leveraging both measured and empirically-based simulation results, this comprehensive approach facilitates the characterization of mass transport resistance distribution along the gas channel. The learnings from this study provide valuable insight into the optimization of channel and materials design for enhancing large active area fuel cell performance and durability.

Influence of the Clamping Force and the Formation of Liquid Water Along the Channel on the Local Diffusion Processes in PEMFCs

A novel measurement setup, technique, and segmented model are introduced to spatially resolve mass transport losses along the channel in a PEMFC. The newly designed segmented cell enables not only the measurement of local current and voltage data but also the capture of local temperature and compression levels. By extending the commonly used limiting current method, the local mass transport resistance is determined as a function of local operating parameters. The local current and temperature are directly measured, while the operating conditions along the channel such as pressure, oxygen fraction, and relative humidity are obtained empirically from a 1-D differential model. Leveraging both measured and empirically-based simulation results, this comprehensive approach facilitates the characterization of mass transport resistance distribution along the gas channel. The learnings from this study provide valuable insight into the optimization of channel and materials design for enhancing large active area fuel cell performance and durability.