Local Concentration Gradients Research Articles

Anisotropic Hollow Structure with Chemotaxis Enabling Intratumoral Autonomic Therapy.

Effective intratumoral drug penetration is pivotal for successful cancer treatment. However, due to the disrupted capillary networks and poor perfusion in solid tumors, there exist challenges to realize autonomous directional drug penetration and controlled drug release within the tumor. Considering the specificity of glucose within tumor tissue, we draw inspiration from nature and engineer asymmetrical hollow structures exhibiting chemotaxis towards high glucose levels. By incorporating multiple shells into these structures, we enhance the local chemical concentration gradients, thereby improving cellular uptake and precise targeting. The advantages of anisotropic hollow multishell structure (a-HoMS) can be reflected from the diffusion coefficient and directivity, which increase by 73.4% and 265% respectively compared to conventional isotropic hollow spheres, achieving the most linear movement while ensuring the speed of movement. Furthermore, the multi-level porosity and temporal-spatial order of a-HoMS enable sequential drug delivery that inhibits angiogenesis with inducing cell apoptosis. After the eradication of localized tumor cells, the a-HoMS can automatically migrate to the alive tumor cells under the glucose gradient, inducing another cycle of drug delivery and chemotaxis, resulting in excellent antitumor efficacy. These anisotropic HoMS demonstrate intelligence, adaptability, and precision in tumor therapy, providing valuable insights for programmable treatment within tissues.

Anisotropic Hollow Structure with Chemotaxis Enabling Intratumoral Autonomic Therapy

Effective intratumoral drug penetration is pivotal for successful cancer treatment. However, due to the disrupted capillary networks and poor perfusion in solid tumors, there exist challenges to realize autonomous directional drug penetration and controlled drug release within the tumor. Considering the specificity of glucose within tumor tissue, we draw inspiration from nature and engineer asymmetrical hollow structures exhibiting chemotaxis towards high glucose levels. By incorporating multiple shells into these structures, we enhance the local chemical concentration gradients, thereby improving cellular uptake and precise targeting. The advantages of anisotropic hollow multishell structure (a‐HoMS) can be reflected from the diffusion coefficient and directivity, which increase by 73.4% and 265% respectively compared to conventional isotropic hollow spheres, achieving the most linear movement while ensuring the speed of movement. Furthermore, the multi‐level porosity and temporal‐spatial order of a‐HoMS enable sequential drug delivery that inhibits angiogenesis with inducing cell apoptosis. After the eradication of localized tumor cells, the a‐HoMS can automatically migrate to the alive tumor cells under the glucose gradient, inducing another cycle of drug delivery and chemotaxis, resulting in excellent antitumor efficacy. These anisotropic HoMS demonstrate intelligence, adaptability, and precision in tumor therapy, providing valuable insights for programmable treatment within tissues.

Mechanistic insights into how mixing factors govern polyelectrolyte-surfactant complexation in RNA lipid nanoparticle formulation

Hypothesis: Lipid nanoparticle self-assembly is a complex process that relies on ion pairing between nucleic acids and hydrophobic cationic lipid counterions for encapsulation. The chemical factors influencing this process, such as formulation composition, have been the focus of recent research. However, the physical factors, particularly the mixing protocol, which directly modulates these chemical factors, have yet to be mechanistically examined using a reproducible mixing platform comparable to the industry standard. We here utilize Flash NanoPrecipitation (FNP), a scalable rapid mixing platform, to isolate and systematically investigate how mixing factors influence this complexation step, first by using a model polyelectrolyte-surfactant system and then generalizing to a typical RNA lipid nanoparticle formulation.Experiments: Aqueous polystyrene sulfonate (PSS) and cetrimonium bromide (CTAB) solutions are rapidly homogenized using reproducible FNP mixing and controlled flow rates at different stoichiometric ratios and total solids concentrations to form polyelectrolyte-surfactant complexes (PESCs). Then, key mixing factors such as total flow rate, inlet stream relative volumetric flow rate, and magnitude of flow fluctuation are studied using both this PESC system and an RNA lipid nanoparticle formulation.Findings: Fluctuations in flow as low as ± 5 % of the total flow rate are found to severely compromise PESC formation. This result is replicated in the RNA lipid nanoparticle system, which exhibited significant differences in size (132.7 nm vs. 75.6 nm) and RNA encapsulation efficiency (34.0 % vs. 82.8 %) under fluctuating vs. steady flow. We explain these results in light of the chemical variables isolated and studied; slow or nonuniform mixing generates localized concentration gradients that disrupt the balance between the hydrophobic and electrostatic forces that drive complex formation. These experiments contribute to our understanding of the complexation stage of lipid nanoparticle formation and provide practical insights into the importance of developing controlled mixing protocols in industry.

Nanoscopic Imaging of Self-Propelled Ultrasmall Catalytic Nanomotors.

Ultrasmall nanomotors (<100 nm) are highly desirable nanomachines for their size-specific advantages over their larger counterparts in applications spanning nanomedicine, directed assembly, active sensing, and environmental remediation. While there are extensive studies on motors larger than 100 nm, the design and understanding of ultrasmall nanomotors have been scant due to the lack of high-resolution imaging of their propelled motions with orientation and shape details resolved. Here, we report the imaging of the propelled motions of catalytically powered ultrasmall nanomotors─hundreds of them─at the nanometer resolution using liquid-phase transmission electron microscopy. These nanomotors are Pt nanoparticles of asymmetric shapes ("tadpoles" and "boomerangs"), which are colloidally synthesized and observed to be fueled by the catalyzed decomposition of NaBH4 in solution. Statistical analysis of the orientation and position trajectories of fueled and unfueled motors, coupled with finite element simulation, reveals that the shape asymmetry alone is sufficient to induce local chemical concentration gradient and self-diffusiophoresis to act against random Brownian motion. Our work elucidates the colloidal design and fundamental forces involved in the motions of ultrasmall nanomotors, which hold promise as active nanomachines to perform tasks in confined environments such as drug delivery and chemical sensing.

Interfacial salt effect induced by competitive adsorption of coexisting ions: A new understanding of the mass transfer selectivity in the near-interface boundary layer

Specific ion effects are known to influence the interfacial behavior of ions in the aqueous phase and thus affect their extraction and separation. There are many studies on enhanced extraction and separation of the target ions based on the specific ion effects. A microscopic level understanding of the competitive mass transfer and selectivity of ions at the interface between heterogeneous phases is crucial importance for the precise control of numerous chemical reaction and separation processes. The conventional salt effect (i.e., background coexisting ions promoting the mass transfer of the target ions) are only observed at higher coexisting ion concentrations. However, the present work reveals an interesting phenomenon: the adsorption enrichment and competitive hydration of coexisting salt cations at the liquid–liquid interface can significantly influence the mass transfer rate of the target rare earth ions in the near-interface boundary layer. Notably, such a distinct interfacial salt effect can promote the separation between coexisting and target ions at lower coexisting ion concentrations, and it cannot be explained by the traditional theory for the salt effect. A thin-layer organic oil film extraction system was employed here as a simplified model experiment to investigate this new interfacial salt effect on the non-equilibrium extraction and separation of target rare earth ions. The results demonstrated that the diffusion rate of the target ions (Er3+) is subject to the local concentration gradient of coexisting salt cations (Mg2+) in the near-interface boundary layer. At the lower bulk concentrations, the Mg2+ ions enriched at the interface would compete for water molecules around the hydration shell of target Er3+ ions, resulting in the dehydration of Er3+ ions. Therefore, an enhanced diffusion rate of Er3+ ions and their adsorption affinity towards the interface were observed. However, at a higher bulk concentration of Mg2+ ions, the diffusion resistance of Er3+ ions increased due to the competitive adsorption and hydration of Mg2+ ions at the interface. The thickness of the organic oil film layer also plays an important role in the diffusion of Er3+ ions. In particular, a thinner oil layer makes it easier to perceive the interfacial salt effect, which enhances the separation between Er3+ and Mg2+ compared to the case of a thicker oil layer. A quantitative correlation between the diffusion rate of Er3+ ions and the concentration of coexisting Mg2+ ions was established to describe the interfacial salt effect. This work highlights the microscopic nature of the salt effect induced by the competitive adsorption kinetics of coexisting ions in the near-interface boundary layer on promoting the extraction and separation of target metal ions. The results will help the development of new approaches to control the separation selectivity and enhance the mass transfer of target metal ions in practical applications.

Differential controls on CO2 and CH4 emissions from the free-flowing Neretva River, Bosnia and Herzegovina

Streams and rivers emit methane (CH4) and carbon dioxide (CO2), two greenhouse gasses contributing to global warming. Estimates for diffusive gas emissions can be obtained by multiplying the concentration gradient between water and atmosphere with the gas transfer velocity. The latter is purely physically constrained, yet spatially highly variable. And - in a flowing water ecosystem - the local concentration gradient is the result of a dynamic balance between upstream evasion and resupply. The collection of representative emission data is thus challenging and emissions of river ecosystems are rarely assessed considering temporal variability and spatial dependence at network scale. In this study, we uncover spatial heterogeneity and controls of concentrations and emission fluxes of the two greenhouse gasses, CH4 and CO2, along a 50 km length of a pristine river system, the Neretva River in Bosnia and Herzegovina. This remote river network has so far remained barely influenced by human activities and the hydromorphological status is to date not altered. The Neretva can therefore serve as a reference for similar systems in the region. This seems to be particularly important as rivers in the Western Balkans, including the Neretva, are currently experiencing a surge in hydropower development and damming, which is known to strongly affect riverine greenhouse gas emissions. We found high emissions as a result of co-occurrence of high concentration with high exchange velocity, but we identified different underlying mechanistic processes driving the evasion of the two gasses. CH4 was strongly supply-limited: elevated concentrations were exclusively measured in a large pool (0.84 µmol L-1 compared to a median concentration of 0.005 µmol L-1 in the entire study section). This resulted in CH4 evasion being four orders of magnitude higher in the turbulent reach following the pool (22 mmol m-2 d-1) compared to the median evasion at network scale (0.06 mmol m-2 d-1). In contrast, CO2 evasion was more variable in time and equally dependent on CO2 and gas exchange velocity. The construction of dams intended in this area would lead to reservoirs of slowly flowing or standing water with similar habitat conditions as the observed CH4-hotspot. The concomitant increase in residence time and higher retention of organic material will lead to an increase of CH4 production replacing aerobic respiration. Consequently, CH4 emissions can be expected to drastically increase by orders of magnitude. This greenhouse gas footprint of hydropower generation may counteract the promised climate benefits in terms of renewable energy production.

Reactant enrichment in yolk-shell structured Pd/TiN nanoreactors for boosting electrocatalytic hydrodechlorination performance

Enhancing the enrichment behavior of low-concentration chlorinated organic pollutants remains a significant challenge in electrocatalytic hydrodechlorination (EHDC) technology. Metal-loaded hollow nanoarchitecture has emerged as a promising nanoreactor to improve reaction enrichment behavior because of its tailorable microenvironments and electronic properties. Herein, a structural engineering strategy is developed to synthesize yolk-shell structured TiN spheres supported Pd nanoreactors (Pd/YS-TiN) with confined mesoscopic spaces. Characterization by multiple techniques reveals that the yolk-shell structure of YS-TiN, with high specific surface area (139.0 m2/g) and appropriately mesoporosity (6.9 nm), exposes numerous Pd nanoparticles (∼4.0 nm) on outer/inner surface of the shell and yolk-core solid sphere, ensuring an efficient utilization of active sites for enhancing the 2,4-DCP detoxification. Consequently, the structurally optimized Pd/YS-TiN nanoreactor consistently displays maximum reaction kinetics, dechlorination degree, faradaic current density, H* utilization and product selectivity, surpassing hollow TiN-supported Pd and Pd/C catalysts. The super EHDC performance of 91.8 % 2,4-DCP conversion, a specific activity of 1.68 min−1 molPd−1, and a mass activity of 6.06 min−1 gPd−1 is obtained at −0.85 V and 180 min, outperforming most reported catalysts. Combining experimental and density functional theory results, the exceptional reaction enrichment behavior of Pd/YS-TiN originates from (1) alleviating the overstrong adsorption of product phenol through strong metal-support interactions and (2) enhancing mass transport efficiency facilitated by the local concentration gradient and mesoporous shell. This study elucidates how metal-support interactions and mass transport synergistically enhance reaction enrichment behavior, showcasing potential benefits in environmental remediation applications.

Frameworked electrolytes: Ionic transport behavior and high mobility for solid state batteries

AbstractAll solid‐state batteries (ASSBs) are the holy grails of rechargeable batteries, where extensive searches are ongoing in the pursuit of ideal solid‐state electrolytes. Nevertheless, there is still a long way off to the satisfactorily high (enough) ionic conductivity, long‐term stability and especially being able to form compatible interfaces with the solid electrodes. Herein, we have explored ionic transport behavior and high mobility in the sub‐nano pore networks in the framework structures. Macroscopically, the frameworked electrolyte behaves as a solid, and however in the (sub)‐nano scales, the very limited number of solvent molecules in confinement makes them completely different from that in liquid electrolyte. Differentiated from a liquid‐electrolyte counterpart, the interactions between the mobile ions and surrounding molecules are subject to dramatic changes, leading to a high ionic conductivity at room temperature with a low activation energy. Li+ ions in the sub‐nano cages of the network structure are highly mobile and diffuse rather independently, where the rate‐limiting step of ions crossing cages is driven by the local concentration gradient and the electrostatic interactions between Li+ ions. This new class of frameworked electrolytes (FEs) with both high ionic conductivity and desirable interface with solid electrodes are demonstrated to work with Li‐ion batteries, where the ASSB with LiFePO4 shows a highly stable electrochemical performance of over 450 cycles at 2°C at room temperature, with an almost negligible capacity fade of 0.03‰ each cycle. In addition, the FE shows outstanding flexibility and anti‐flammability, which are among the key requirements of large‐scale applications.image

Microfluidic 3D hepatic cultures integrated with a droplet-based bioanalysis unit

A common challenge in microfluidic cell cultures has to do with analysis of cell function without replacing a significant fraction of the culture volume and disturbing local concentration gradients of signals. To address this challenge, we developed a microfluidic cell culture device with an integrated bioanalysis unit to enable on-chip analysis of picoliter volumes of cell-conditioned media. The culture module consisted of an array of 140 microwells with a diameter of 300 m which were made low-binding to promote organization of cells into 3D spheroids. The bioanalysis module contained a droplet generator unit, 15 micromechanical valves and reservoirs loaded with reagents. Each 0.8 nL droplet contained an aliquot of conditioned media mixed with assay reagents. The use of microvalves allowed us to load enzymatic assay and immunoassay into sequentially generated droplets for detection of glucose and albumin, respectively. As a biological application of the microfluidic device, we evaluated hormonal stimulation and glucose consumption of hepatic spheroids. To mimic physiological processes occurring during feeding and fasting, hepatic spheroids were exposed to pancreatic hormones, insulin or glucagon. The droplet-based bioanalysis module was used to measure uptake or release of glucose upon hormonal stimulation. In the future, we intend to use this microfluidic device to mimic and measure pathophysiological processes associated with hepatic insulin resistance and diabetes in the context of metabolic syndrome.

PH-Sensitive Glucose-Powered Nanomotors for Enhanced Intracellular Drug Delivery and Ferroptosis Efficiency.

We propose a glucose-powered Janus nanomotor where two faces are functionalized with glucose oxidase (GOx) and polydopamine-Fe3+ chelates (PDF), respectively. In the glucose fuel solution, the GOx on the one side of these Janus nanomotors catalytically decomposes glucose fuels into gluconic acid and hydrogen peroxide (H2 O2 ) to drive them at a speed of 2.67 μm/s. The underlying propulsion mechanism is the glucose-based self-diffusiophoresis owing to the generated local glucose concentration gradient by the enzymatic reaction. Based on the enhanced diffusion motion, such nanomotors with catalytic activity increase the uptake towards cells and subsequently exhibit excellent capabilities for Fe3+ ions delivery and H2 O2 generation for enhancing ferroptosis efficiency for inducing cancer cell death. In particular, the Fe3+ ions are released from nanomotors in a slightly acidic environment, and subsequently generate toxic hydroxyl radicals via Fenton reactions, which accumulation reactive oxygen species (ROS) level (~300 %) and further lipid peroxidation (LPO) strengthened ferroptosis therapy for cancer treatment. The as-developed glucose-powered Janus nanomotor with efficient diffusion and Fe ions delivery capabilities show great promise as a potential in biomedical applications.

Diffusiophoresis-enhanced particle deposition for additive manufacturing.

The ability to govern particle assembly in an evaporative-driven additive manufacturing (AM) can realize multi-scale features fundamental to creating printed electronics. However, existing techniques remain challenging and often require templates or contaminating solutes. We explore the control of particle deposition in 3D-printed colloids by diffusiophoresis, a previously unexplored mechanism in multi-scale AM. Diffusiophoresis can introduce spontaneous phoretic particle motion by establishing local solute concentration gradients. We show that diffusiophoresis can play a dominant role in complex evaporative-driven particle assembly, enabling a fundamentally new and versatile control of particle deposition in a multi-scale AM process.

Reactant enrichment in hollow void of Pt NPs@MnOx nanoreactors for boosting hydrogenation performance.

In confined mesoscopic spaces, the unraveling of a catalytic mechanism with complex mass transfer and adsorption processes such as reactant enrichment is a great challenge. In this study, a hollow nanoarchitecture of MnOx-encapsulated Pt nanoparticles was designed as a nanoreactor to investigate the reactant enrichment in a mesoscopic hollow void. By employing advanced characterization techniques, we found that the reactant-enrichment behavior is derived from directional diffusion of the reactant driven through the local concentration gradient and this increased the amount of reactant. Combining experimental results with density functional theory calculations, the superior cinnamyl alcohol (COL) selectivity originates from the selective adsorption of cinnamaldehyde (CAL) and the rapid formation and desorption of COL in the MnOx shell. The superb performance of 95% CAL conversion and 95% COL selectivity is obtained at only 0.5MPa H2 and 40min. Our findings showcase that a rationally designed nanoreactor could boost catalytic performance in chemoselective hydrogenation, which can be of great aid and potential in various application scenarios.

Achieving multi-dimensional Li+ transport nanochannels via spatial-partitioning in crystalline ionic covalent organic frameworks for highly stable lithium metal anode

The fragile solid electrolyte interphase (SEI) and anisotropic dendrite growth during Li plating/stripping have posed as intractable handicaps to the practical implementation of lithium metal batteries (LMBs). The Li+ uniform distribution and unimpeded transfer play significant roles to enable protuberance-free Li textures. Herein, the highly-crystalline TFSI− ionic-covalent organic framework (I-COF) endowed with designated mixed-dimensional channels was constructed as an artificial SEI layer via anionic post-modification. Benefiting from the desirable spatial-partitioning effect triggered by nanochannels reconfiguration, the I-COF with expanded multi-dimensional Li+ transport channels and scaled-down pore volume could effectively disperse the local concentration gradient of Li+ flux and inhibit growth of Li dendrites. Besides, the coordinated TFSI− anions with a high tLi+ of 0.76 can selectively restrict the delivery and decomposition of homogeneous ions. To understand the interfacial charge transfer mechanisms, the lithophilic properties and the energy barriers for Li+ migration were also calculated. Correspondingly, the I-COF(TI−) modified Li|Li symmetric cell showed superb durability over 5500 h at 4 mA cm−2 with extraordinary overpotential. The Li|S full cell also displayed prolonged lifespan and excellent rate performance. The comprehension of the mixed-dimensional interfacial strategy via spatial-partitioning provides new insights into the fabrication of solid–solid interfaces, which can aid in the improved design and development of advanced lithium-metal batteries (LMBs).

Steering CO2 electrolysis selectivity by modulating the local reaction environment: An online DEMS approach for Cu electrodes

Electrochemical CO2 reduction is a typical surface-mediated reaction, with its reaction kinetics and product distributions largely dependent on the dynamic evolution of reactive species at the cathode–catholyte interface and on the resultant mass transport within the hydrodynamic boundary layer in the vicinity of the cathode. To resolve the complex local reaction environment of branching CO2 reduction pathways, we here present a differential electrochemical mass spectroscopic (DEMS) approach for Cu electrodes to investigate CO2 mass transport, the local concentration gradients of buffering anions, and the Cu surface topology effects on CO2 electrolysis selectivity at a temporal resolution of ∼400 ​ms. As a proof of concept, these tuning knobs were validated on an anion exchange membrane electrolyzer, which delivered a Faradaic efficiency of up to 40.4% and a partial current density of 121 ​mA ​cm−2 for CO2-to-C2H4 valorization. This methodology, which bridges the study of fundamental surface electrochemistry and the upgrading of practical electrolyzer performance, could be of general interest in helping to achieve a sustainable circular carbon economy.

The role of variable zeta potential on diffusiophoretic and diffusioosmotic transport

Diffusiophoresis is the spontaneous motion of colloidal particles induced by the presence of a local solute concentration gradient, and diffusioosmosis is the analogous motion of fluid near a surface. The zeta potential, a measure of the electrokinetic potential at the slipping plane in the Debye layer, plays an important role in these processes, as it is a measure of the strength of interactions between solute and surface molecules. Many previous studies on diffusiophoresis/diffusioosmosis have relied on the assumption of constant zeta potential, in part due to the significant theoretical simplification introduced by this assumption. However, in general the zeta potential varies as a function of solute concentration, which often varies by orders of magnitude in typical setups. We seek to characterize the role of variable zeta potential on diffusiophoresis/diffusioosmosis by revisiting recent studies that treated zeta potential as constant. For each case, we characterize and quantify the change in the particle/solute/fluid dynamics when a variable zeta potential model is considered. The four test problems that are considered are: (1) diffusiophoresis-induced particle banding in a stopped-flow diffusion cell, (2) one-dimensional particle injection in a dead-end pore, (3) arrested particle spreading in a solute/particle co-diffusion system, and (4) diffusioosmotic pumping in a micropore connecting solute streams. The results provide examples of the qualitative and quantitative differences that can result when using materials that satisfy constant potential, constant charge, or even charge-regulating surface properties, and stress the importance of selecting the appropriate surface model. This work provides guidance to experimentalists and modelers in selecting efficient and accurate models for their diffusiophoretic/diffusioosmotic systems, and these results indicate that finite Debye layer effects typically affect transport much more than variable zeta potential effects, but detailed problem-specific simulations are needed to quantify these effects.

Critical verification of the effective diffusion concept

Knowing the hydrogen distribution c(x,t) and local hydrogen concentration gradients grad(c) in ferritic steel components is crucial with respect to hydrogen embrittlement. Basically, hydrogen is absorbed from corrosive or gaseous environments via the surface and diffuses through interstitial lattice sites into bulk. Although, the lattice diffusion coefficient DL∼0.01mm2/s is in the order of magnitude of those for well-annealed pure iron, trapping sites in the microstructure retard the long-range chemical diffusion jL=−Dchem(c)grad(c), causing local hydrogen accumulation in near surface regions in limited time. Considering pure ferritic crystals without trapping sites in the microstructure, the limited characteristic diffusion depth xc∼Defft is proportional to the square root of the effective diffusion coefficient Deff and of time t. Effective diffusion coefficients are measured independently for hydrogen using the electrochemical permeation technique. For pure crystals, the effective diffusion coefficient is constant at given temperature and allows accurate calculations of the diffusion depths. However, with trapping sites in the microstructure the effective diffusion coefficient is not a material property anymore and becomes dependent on the hydrogen charging conditions. In the present work, the theory of hydrogen bulk diffusion is used to verify the concept of effective diffusion. For that purpose, the generalized bulk diffusion equation was solved numerically by using the finite difference method (FDM). The implementation was checked using analytical solutions and a comprehensive convergence study was done to avoid mesh and time dependency of the results. It is shown that effective diffusion coefficients can vary by magnitudes depending on the sub-surface lattice concentration. This limits the application of the effective diffusion concept and also the calculation of the characteristic diffusion depth.

Role of surfactant-induced Marangoni effects in droplet dynamics on a solid surface in shear flow

We address the dynamics of a surfactant-laden droplet on a solid surface in simple shear flow numerically. Our analysis uses the front-tracking method to take surfactant transport into account. The interfacial tension and the slip coefficient, both of which depend heavily on the surfactant concentration, are fully integrated into the generalized Navier boundary condition to model the moving contact lines. Accurate prediction of droplet motion indicates that the surfactant can change droplet behavior drastically. Surfactant-induced effects, such as interfacial tension reduction, the Marangoni stress, and wettability alternation, are investigated for various capillary numbers, surface wettabilities, elasticity numbers, and surface Péclet numbers. Deformation and motion of a sliding droplet are enhanced by the Marangoni effect, which is associated with an interfacial tension gradient. When the capillary number reaches a critical value, the sliding-to-detachment and detachment-to-pinch-off transitions occur. Both transitions can be triggered and accelerated by a surfactant, especially when convection is dominant. As a result, the critical capillary number decreases, but exhibits a non-monotonic relationship with the elasticity number and Péclet number. The mechanisms that underlie the effect of Marangoni stress are discussed by analyzing the distributions of the surfactant concentration and the hydrodynamic forces exerted on the droplet. Accumulation of surfactants near the receding contact line reverses the local concentration gradient, attempts to change its direction along the interface, and delays droplet detachment. Furthermore, the strong surfactant dilution reduces both the surfactant concentration and the interfacial tension gradient, and thereby increasing the critical value for droplet pinch-off.

3D Modeling of the Adsorption Rate of Pyridine on Activated Carbon Cloth in a Stirred Tank under Turbulent Conditions

The experimental and numerical analysis of pyridine adsorption onto activated carbon cloth in a stirred batch adsorber under transition and turbulent regime is presented in this work. Three-dimensional numerical modeling of the adsorption process was implemented for the identification of local velocity, local concentration, and concentration gradients inside the adsorber. This represents a costly computational effort in comparison with conventional batch adsorption models, as for instance the Langmuir kinetic model. Both types of modeling yield comparable results, but the advantage of the 3D modeling is a more detailed resolution of variables, thus avoiding the perfectly mixed assumption. Varying the agitation rate (30–200 rpm) and pyridine initial concentration (99 to 487 mg/L), several kinetic and transport parameters were reported. Hydrodynamic and mass boundary layers are identified around the activated carbon adsorbent following the trajectory of agitation. Furthermore, the major pyridine mass flux takes place around the adsorbent, mainly in the posterior zone regarding the agitation direction. This information is crucial in searching for and designing more efficient and intensive adsorbent systems.

Numerical calculation of lithiation-induced stress in a spherical electrode: Effect of lithiation-induced structural damage

The improvement of the long-time stability of metal-ion batteries requires the understanding of structural integrity of electrode materials during electrochemical cycling. Using the correlation between damage state variable, local concentration and concentration gradient of solute atoms proposed by Yang [Journal of Energy Storage 45 (2022) 103748], we analyze the effects of lithiation-induced structural damage/degradation on the stress evolution in a spherical electrode in the framework of linear elasticity with the coupling between diffusion and stress under respective potentiostatic and galvanostatic operation. Without the contribution of the concentration gradient to structural damage/degradation, the effective stress exhibits an increasing trend, reaches local maximum and then decreases with the increase of the lithiation time at a spatial position away from the center of the spherical electrode for both the potentiostatic and galvanostatic operations. The largest maximum effective stress is present at the surface of the spherical electrode immediately after the onset of the lithiation for potentiostatic operation and inside the spherical electrode for galvanostatic operation. The concentration gradient causes less structural damage/degradation under galvanostatic operation than under photentiostatic operation due to that galvanostatic operation introduces less concentration gradient than potentiostatic operation.

Strain induced crack initiation and the subsequent crack propagation of fiber-reinforced resin composites

Fiber-reinforced composite is a kind of excellent lightweight material that has important applications in the fields of aerospace, automotive, etc. However, due to the strong heterogeneous characteristics of its internal microstructures, material properties dramatically changed interfaces, and the rapid brittle damage process, its internal deformation and failure mechanism is a current hot research topic. Here, the synchrotron X-ray computed tomography technology and digital volume correlation method were adopted to investigate the internal three-dimensional deformation and failure evolution of the representative unit of fiber-reinforced resin composites during loading process. It shows that the deformation parameters including the local strain concentration and strain gradient in this fiber-reinforced heterogeneous system have important prediction and guiding effects on crack initiation and the subsequent propagation. These results may have positive significance for revealing the failure mechanisms, as well as microstructure and interface optimization of fiber-reinforced composites.