Diffuse Interface Research Articles

High-performance polyurea nanofiltration membrane for waste lithium-ion batteries recycling: Leveraging synergistic control of bulk and interfacial monomer diffusion

The development of high-performance nanofiltration (NF) membranes with extreme chemical stability is urgently needed for the recovery of spent lithium. In this study, a series of polyurea membranes with high lithium recovery efficiency and pH stability were fabricated by zone-regulated interfacial polymerization (IP). The reaction inhibitor Cu2+ in the bulk aqueous phase reduces IP intensity by reversibly binding to the amino groups of polyethyleneimine monomers through chelate bonds. Meanwhile, surfactant promote the uniform diffusion of macromolecular aqueous monomers at the phase interface. The milder polymerization reaction and the more stable phase interface endow the polyurea membrane (NF10k PEI-SDS-Cu2+) with higher water permeance (2.1 L m−2 h−1 bar−1), desirable MgCl2 rejection (94.7 %), and excellent fabrication repeatability. Moreover, the membrane demonstrates stable separation selectivity for Co2+/Li+ and SO42−/Li+ under conditions of 0.05 mol L−1 H2SO4 and 2 mol L−1 LiOH, respectively. Our study provides a facile method for constructing NF membranes with extreme pH stability and confirms the feasibility of membrane-based lithium recovery.

Microstructure of interfacial diffusion layer of cross-layered silver–copper composite strip and its effect on resistivity

Microstructure of interfacial diffusion layer of cross-layered silver–copper composite strip and its effect on resistivity

Structure, orientation, and dynamics of per- and polyfluoroalkyl substance (PFAS) surfactants at the air-water interface: Molecular-level insights

HypothesisUnderstanding the intricate molecular-level details of toxic per- and polyfluoroalkyl substances (PFAS) partitioning to the air–water interface holds paramount importance in evaluating their fate and transport, as well as for finding safer alternatives for various applications, including aqueous film forming foams. The behavior of these substances at interfaces strongly depends on molecular architecture, chemistry, and concentration, which define molecular packing, self-assembly, interfacial diffusion, and the surface tension. SimulationsModeling of three PFAS surfactants, namely, longer-tail (perfluorooctanoate (PFOA)) and shorter-tail (perfluorobutanoate (PFBA) and 2,3,3,3-tetrafluoro-2-(heptafluoropropoxy) propanoate (GenX)) has been conducted using atomistic molecular dynamics simulations. A systematic comparison between these representative PFAS of different sizes and structure reveals factors influencing their association behavior, mechanism of surface tension reduction, and interfacial mobility as a function of surface coverage. FindingsShorter-chain PFAS surfactants (GenX or PFBA) require lower surface coverage compared to longer chain (PFOA) PFAS to achieve the same decrease in surface tension. However, a higher concentration of GenX and PFBA is necessary in the bulk aqueous solution to achieve the same surface coverage as PFOA, due to their higher solubility in water. The PFAS molecular orientation and mobility at the interface are found to be vastly influenced by the length and architecture of the hydrophobic fluorocarbon tail. A significant ordering of the water dipole moment near the anionic headgroup is apparent at high surface concentration. A direct correlation is established between the PFAS interfacial properties and PFAS-PFAS, PFAS-counterion, and PFAS-water interactions.

Incorporation of TC4 (Ti-6Al-4V) to construct strong interfacial bonding with Mg matrix to achieve improved hydrogen storage kinetics

Effective contact between the catalyst and the Mg/MgH2 matrix is the key to efficiently enhancing the hydrogen storage kinetics. In this work, a Mg-10 wt% TC4 (Ti-6Al-4V) composite with strong interfacial bonding was prepared by vacuum hot pressing sintering, and the reinforcement mechanism of TC4 was investigated. The results indicated that TC4 has a significant improvement effect on the activation efficiency and hydrogen absorption/desorption kinetics. The hydrogen absorption and desorption activation energies of AZ91-TC4 (53.0/111.3 kJ/mol) are 19.6 and 37.2 kJ/mol lower than that of AZ91 without TC4, respectively. Moreover, TC4 can cause AZ91 to start dehydrogenation at 449 K, and the reduction is about 110 K. Except for the increase of grain boundaries and microcracks caused by TC4, the transition diffusion interface formed by TC4 and Mg matrix with a lower diffusion barrier can be used as a special fast diffusion channel to accelerate the hydrogenation process controlled by H atom diffusion. Meanwhile, the kinetic calculations indicate that the dehydrogenation process of AZ91 is controlled by the nucleation and growth step of Mg, and its nucleation activation energy is ca. 4 times the growth activation energy. TC4 and its induced precipitation of TiAl and Al8Mn5 can dramatically accelerate the nucleation process of Mg, resulting in the rate-determining step changing to the surface penetration of H atoms, and the desorption rate is significantly improved. These positive findings provide new tactics for designing excellent hydrogen storage catalysts.

Uniqueness of the blow‐down limit for a triple junction problem

AbstractWe prove the uniqueness of blow‐down limit at infinity for an entire minimizing solution of a planar Allen–Cahn system with a triple‐well potential. Consequently, can be approximated by a triple junction map at infinity. The proof exploits a careful analysis of energy upper and lower bounds, ensuring that the diffuse interface remains within a small neighborhood of the approximated triple junction at all scales.

Diffusion Interface Evolution of Low-Alloy Steel Q235 and Ti by Electro-Assisted Hot-Pressing Bond

Diffusion Interface Evolution of Low-Alloy Steel Q235 and Ti by Electro-Assisted Hot-Pressing Bond

A coated hypotrochoidal compressible liquid inclusion neutral to a hydrostatic stress field after relaxation by interface slip and diffusion

We study the steady-state response of a three-phase composite composed of an internal hypotrochoidal compressible liquid inclusion, an intermediate isotropic elastic coating and an outer isotropic elastic matrix with simultaneous interface slip and diffusion occurring on the solid–solid interface when the matrix is subjected to a uniform hydrostatic stress field. We design a neutral coated hypotrochoidal liquid inclusion that does not disturb the prescribed uniform hydrostatic stress field in the surrounding matrix. The neutrality is achieved when the plane-strain bulk modulus or the compressibility of the elastic matrix is determined by solving a system of simultaneous linear algebraic equations for given geometric and material parameters of the coated liquid inclusion.

Microstructure and properties of Cu matrix composites reinforced with surface-modified Kovar particles

The thermal conductivity of Cu/Kovar composites was improved by suppressing element diffusion at the interfaces through the formation of FeWO4 coating on the Kovar particles via vacuum deposition. Cu matrix composites reinforced with unmodified (Cu/Kovar) and modified Kovar (Cu/Kovar@) particles were prepared by hot pressing. The results demonstrate that the interfaces of Cu/FeWO4 and FeWO4/Kovar in the Cu/Kovar@ composites exhibit strong bonding, and no secondary phase is generated. The presence of FeWO4 impedes interfacial diffusion within the composite, resulting in an increase in grain size and a decrease in dislocation density. After surface modification of the Kovar particle, the thermal conductivity of Cu/Kovar@ composite is increased by 110% from 40.6 to 85.6 W·m−1·K−1. Moreover, the thermal expansion coefficient of the Cu/Kovar@ composite is 9.8×10−6 K−1, meeting the electronic packaging requirements.

Pt thin-film resistance thermo detectors with stable interfaces for potential integration in SiC high-temperature pressure sensors

Due to the excellent mechanical, chemical, and electrical properties of third-generation semiconductor silicon carbide (SiC), pressure sensors utilizing this material might be able to operate in extreme environments with temperatures exceeding 300 °C. However, the significant output drift at elevated temperatures challenges the precision and stability of measurements. Real-time in situ temperature monitoring of the pressure sensor chip is highly important for the accurate compensation of the pressure sensor. In this study, we fabricate platinum (Pt) thin-film resistance temperature detectors (RTDs) on a SiC substrate by incorporating aluminum oxide (Al2O3) as the transition layer and utilizing aluminum nitride (AlN) grooves for alignment through microfabrication techniques. The composite layers strongly adhere to the substrate at temperatures reaching 950 °C, and the interface of the Al2O3/Pt bilayer remains stable at elevated temperatures of approximately 950 °C. This stability contributes to the excellent high-temperature electrical performance of the Pt RTD, enabling it to endure temperatures exceeding 850 °C with good linearity. These characteristics establish a basis for the future integration of Pt RTD in SiC pressure sensors. Furthermore, tests and analyses are conducted on the interfacial diffusion, surface morphological, microstructural, and electrical properties of the Pt films at various annealing temperatures. It can be inferred that the tensile stress and self-diffusion of Pt films lead to the formation of hillocks, ultimately reducing the electrical performance of the Pt thin-film RTD. To increase the upper temperature threshold, steps should be taken to prevent the agglomeration of Pt films.

TexSe1-x Shortwave Infrared Photodiode Arrays with Monolithic Integration.

TexSe1-x shortwave infrared (SWIR) photodetectors show promise for monolithic integration with readout integrated circuits (ROIC), making it a potential alternative to conventional expensive SWIR photodetectors. However, challenges such as a high dark current density and insufficient detection performance hinder their application in large-scale monolithic integration. Herein, we develop a ZnO/TexSe1-x heterojunction photodiode and synergistically address the interfacial elemental diffusion and dangling bonds via inserting a well-selected 0.3 nm amorphous TeO2 interfacial layer. The optimized device achieves a reduced dark current density of -3.5 × 10-5 A cm-2 at -10 mV, a broad response from 300 to 1700 nm, a room-temperature detectivity exceeding 2.03 × 1011 Jones, and a 3 dB bandwidth of 173 kHz. Furthermore, for the first time, we monolithically integrate the TexSe1-x photodiodes on ROIC (64 × 64 pixels) with the largest-scale array among all TexSe1-x-based detectors. Finally, we demonstrate its applications in transmission imaging and substance identification.

Investigating Material Interface Diffusion Phenomena through Graph Neural Networks in Applied Materials.

Understanding and predicting interface diffusion phenomena in materials is crucial for various industrial applications, including semiconductor manufacturing, battery technology, and catalysis. In this study, we propose a novel approach utilizing Graph Neural Networks (GNNs) to investigate and model material interface diffusion. We begin by collecting experimental and simulated data on diffusion coefficients, concentration gradients, and other relevant parameters from diverse material systems. The data are preprocessed, and key features influencing interface diffusion are extracted. Subsequently, we construct a GNN model tailored to the diffusion problem, with a graph representation capturing the atomic structure of materials. The model architecture includes multiple graph convolutional layers for feature aggregation and update, as well as optional graph attention layers to capture complex relationships between atoms. We train and validate the GNN model using the preprocessed data, achieving accurate predictions of diffusion coefficients, diffusion rates, concentration profiles, and potential diffusion pathways. Our approach offers insights into the underlying mechanisms of interface diffusion and provides a valuable tool for optimizing material design and engineering. Additionally, our method offers possible strategies to solve the longstanding problems related to materials interface diffusion.

A self-organized sandwich structure of chromium nitride for ultra-long lifetime in liquid sodium.

The development of fast neutron reactors with improved efficiency and sustainability, being a tangible solution to the large-scale utilization of nuclear energy, serves as a critical step prior to the commercialization of fusion energy. These reactors use liquid metal coolants, which can weaken the durability of metallic components. Conventional design of protective coatings counts upon thermodynamics, which often overlooks the kinetic factors such as structural evolutions, resulting in deteriorated coating properties. Herein, we present a novel interface-engineering strategy involving the control of the phase transformation direction and interface diffusion reaction. Through iterations of self-organization, desired surfaces and interfaces can be achieved for materials used in harsh environments. Specifically, a CrN-coated steel sample with an interfacial Cr layer was designed and fabricated. After ultra-long (up to 6000 h) immersion in liquid sodium, the CrN/Cr coating structure was converted into a sandwich Cr2N/CrN/Cr2N structure dynamically. As a consequence, the coating system exhibited enhanced properties, namely increased surface hardness (by ∼36%), reduced coefficient of friction (by ∼13%), and enhanced interfacial adhesion (by ∼37%). Thus, the proposed strategy can guide the future design of robust coatings with ultra-long service life in harsh environments.

Electrochemical-mechanical coupled interfacial degradation model of Ternary polymer composite cathodes in all-solid-state batteries

Despite significant attention focused on the composite cathode composed of active particles, which is considered to increase the interfacial areas and satisfy high areal load, suffers from interfacial issues. In this article, we formulate an electrochemical-mechanical model of LiNixMnyCozO2 (NMC) composite cathode coupling the relations between interfacial degradation, charge transformation, diffusion transport, and mechanical deformation under cyclic loads. Based on the transition state theory, we regard the interfacial degradation as an energy barrier dependent on the interfacial debonding state. Physical mismatch due to chemical expansion results in interfacial current distinction, anisotropic Li diffusion and excessive local stress. Compared to single-crystal NMC particles, the effect of interfacial separation and internal cracks triggers an extremely nonuniformity of Li distribution within random orientation polycrystalline-type particles. The external pressure in the range of operation can cause mechanical deformation to fill in the interface vacancies, which effectively alleviates the rapid growth of damage and provides a better cyclic performance. Moreover, soft polymer-based solid electrolytes take advantage of their flexible property to deal with solid-solid contact, providing considerable maintenance of interface stability. This present framework reveals the failure mechanism with electrochemical-mechanical coupled relations for composite cathode materials and broadens the design guidance toward improving interfacial integrity.

Chemo-elasto-electro free energy of non-uniform system in the diffuse interface context

In the present work, we propose an alternative approach for deriving the free energy formulation of a non-uniform system. Compared with the work of Cahn and Hilliard (1958 J.Chem. Phys.28258-67), our approach provides a more comprehensive explanation for the individual energy contribution in a non-uniform system, including entropy, interaction energy, and internal energy. By employing a fundamental mathematical calculus, we reformulate the local composition within the interface region. Utilizing the reformulated local composition as well as classic thermodynamic principles, we establish formal expressions for entropy, interaction energy, and the internal energy, which are functions of both composition and composition gradients. We obtain a comprehensive free energy expression for a non-uniform system by integrating these energy density formulations. The obtained free energy expression is consistent with the formula type of Cahn and Hilliard and prodives more deeper physical interpretation. Moreover, using the same approach, we derive formulations for elastic energy and electric potential energy in a non-uniform system. However, the proposed approach encounters a limitation in the special case of a non-uniform fluid contacting a solid substrate. Due to the significant difference in the length scales between the solid-fluid and fluid-fluid interfaces, the wall free energy formulation based on the aforementioned concept is unsuitable for this multi-scale system. To address this limitation, we reformulate the wall free energy as a function of the average composition over the solid-fluid interface. Additionally, the previous derivation relies on an artificial treatment of describing the composition variation across the interface by a smooth monotone function, while the true nature of this variation remains unclear. By utilizing the concept of average composition, we circumvent the open question of how the composition varies across the interface region. Our work provides a thorough understanding for the construction of free energy formulations for a non-uniform system in condensed matter physics.

Effects of interfacial oxygen diffusion on the magnetic properties and thermal stability of Pd/CoFeB/Pd/Ta heterostructure

We investigated the effects of annealing temperatures (TA) on a Pd (5 nm)/CoFeB (10 nm)/Pd (3 nm)/Ta (10 nm) multilayer structure. The as-deposited sample showed an amorphous state with in-plane uniaxial magnetic anisotropy (UMA), resulting in low coercivity and moderate Gilbert damping constant (α) values. Increasing TA led to crystallization, forming bcc-CoFe (110) crystals, which increased in-plane coercivity and introduced isotropic magnetic anisotropy, slightly reducing the α. The two-fold UMA persists up to 600 °C, and the thermal stability of the in-plane magnetic anisotropy remains intact even TA = 700 °C. The TA significantly influenced the magnetic properties such as in-plane saturation magnetization (Ms//), in-plane and out-of-plane coercivities (Hc// and Hc⊥), and in-plane effective magnetic anisotropy energy density (Keff). Above 600 °C, Keff decreased, indicating a transition towards uniaxial perpendicular magnetic anisotropy. Interfacial oxidation and diffusion from the Ta capping layer to the Pd/CoFeB/Pd interfaces were observed, influencing chemical bonding states. Annealing at 700 °C, reduced oxygen within TaOx through a redox reaction involving Ta crystallization, forming TaB, PdO, and BOx states. Ferromagnetic resonance spectra analysis indicated variations in resonance field (Hr) due to local chemical environments. The α reduction, reaching a minimum at 300 °C annealing, was attributed to reduced structural disorder from inhomogeneities. Tailoring magnetic anisotropy and spin dynamic properties in Pd/CoFeB/Pd/Ta structures through TA-controlled oxygen diffusion/oxidation highlights their potential for SOT, DMI, and magnetic skyrmion-based spintronic devices.

Influence of compression effect on the MEA structure and performance based on M−N–C electrocatalysts for PEMFC

The single-atom dispersed active sites and the thicker catalytic layer of metal-nitrogen-carbon (M-N-C) electrocatalysts based membrane electrode assembly (MEA) exhibit notable distinctions from Pt-based MEA, necessitating targeted optimization. This study systematically investigates the influence of compression on both structure and performance of the M-N-C electrocatalysts based MEA. Four compression ratios, ranging from 11.5% to 39.3%, were examined across diverse operational conditions. The variations in impedance across different electrochemical regions are observed, resulting from the superposition of distinct impedance components. It is found that the insufficient compression leads to higher porosity and the formation of cracks between catalytic layer and membrane, adversely impacting internal resistance and proton transport. Increasing compression first acts the catalytic layer, and then gradually acts on the interface, membrane and gas diffusion layer, thereby reducing internal resistance, charge transfer resistances, albeit at the expense of heightened mass transfer resistance. Among these factors, the influence of internal resistance affects significance to total performance. Furthermore, compression influenced mass transfer differently in various layers. For the catalyst layer, the effect was uniform and sustained, while for the gas diffusion layer, it initially remained constant and then experienced a sudden deterioration over a certain extent. Optimal MEA performance is achieved when the compression ratio attains 40 %, which 2.1 times higher than the low compression MEA. This finding emphasizes the necessity for higher compression on M-N-C electrocatalysts based MEA compared to Pt-based MEA.

Revealing the coarsening behavior of precipitates and its effect on the thermal stability in Tʹ and ηʹ dual-phase strengthened Al-Zn-Mg-Cu alloys

High-strength Al-Zn-Mg-Cu alloys are widely utilized, but their strength deteriorates as strengthening precipitates coarsen rapidly at elevated temperatures, limiting their applications above 150°C. This study systematically investigates the microstructure evolution and its impact on the properties of peak-aged Al-Zn-Mg-Cu alloys with varying Zn/Mg ratios during thermal exposure at a series of temperatures from 150 to 300°C for 500 h. The results reveal that alloys A1 and A2 with an optimal Zn/Mg ratio (1.50−2.14) and relatively lower (Zn + Mg) content (7.0−8.8 wt.%), exhibit superior heat resistance properties compared to the other three alloys. Despite having lower strength relative to alloys with higher solute content, peak-aged alloys A1 and A2 retain the highest strength after thermal exposure. This performance is attributed to the high proportion (over 80%) of T′/T phases in the precipitates for alloys A1 and A2, which demonstrate better thermal stability in comparison to η′/η phases. Additionally, the lower solute content reduces the driving force for diffusion of Zn and Mg atoms, thus inhibiting the coarsening of precipitates. Moreover, the study elucidates that the coarsening mechanism of precipitates transitions from interfacial diffusion control at 150°C to matrix diffusion control at 200−300°C. These insights into the composition-dependent coarsening behavior of precipitates in dual-phase strengthened Al-Zn-Mg-Cu alloys offer valuable guidance for designing heat-resistant aluminum alloys with enhanced performance at elevated temperatures.

Comparison of Sharp and Diffuse Interface Methods for Radially Symmetric Compressible Multi-Medium Fluid Flows

Comparison of Sharp and Diffuse Interface Methods for Radially Symmetric Compressible Multi-Medium Fluid Flows

Effect of annealing temperature on interface diffusion behavior of ultra-thin Cu/Al composite sheet by secondary micro-rolling

In this paper, the effect of different annealing temperatures on the interface diffusion behavior of ultra-thin Cu/Al composite sheets was studied. The ultra-thin Cu/Al composite sheet of 0.04 mm was successfully prepared by micro-rolling. The results show that with the increase of annealing temperature, the thickness of diffusion layer increases and the grain size of Cu and Al increases, the interface diffusion of Cu/Al becomes more sufficient. Comparison of diffusion layer thickness between secondary micro-rolling ultra-thin Cu/Al composite sheet and primary micro-rolling ultra-thin Cu/Al composite sheet at the same annealing temperature, the thickness of the interface diffusion layer decreases at the annealing temperature of 360℃ and 400℃, but increases at the annealing temperature of 440℃. The intermetallic compounds CuAl2, Cu4Al and Cu9Al4 are formed at the annealing temperature of 360, 400 and 440℃ after primary micro-rolling ultra-thin Cu/Al composite sheet. Intermetallic compounds CuAl2, Cu4Al and Cu9Al4 were formed at the annealing temperature of 360℃, and intermetallic compounds CuAl2, Cu4Al, Cu9Al4 and CuAl were formed at at the annealing temperature of 400℃ and 440℃ after secondary micro-rolling of ultra-thin Cu/Al composite sheet.

Self-chemophoresis in the thin diffuse interface approximation

Self-chemophoresis is an appealing and quite successful interpretation of the motility exhibited by certain chemically active colloidal particles suspended in a solution of their ‘fuel’: the particle has a phoretic response to self-generated, rather than externally imposed, inhomogeneities in the chemical composition of the solution. The postulated mechanism of chemophoresis is the interaction of the particle (via an adsorption potential) with the chemical inhomogeneities in the surrounding medium. When the range of this interaction is much smaller than any other relevant scale in the system, the (translational and rotational) phoretic velocities can be described in terms of a phoretic coefficient and a slip fluid velocity at the surface of the particle. Using the case of a spherical particle as a simple and physically insightful example, here we exploit an integral representation of the rigid-body motion to critically re-examine this framework. The systematic analysis highlights two steps in the approximation: first the thin–layer approximation (very large particle size), and subsequently a lubrication approximation (slow variation of the adsorption potential along the tangential direction). We also discuss how these approximations could be relaxed and the effect of this on the particle's motion.