Reduced Diffusion Coefficient Research Articles

High-temperature capacitive energy stroage in polymer nanocomposites through nanoconfinement

Polymeric-based dielectric materials hold great potential as energy storage media in electrostatic capacitors. However, the inferior thermal resistance of polymers leads to severely degraded dielectric energy storage capabilities at elevated temperatures, limiting their applications in harsh environments. Here we present a flexible laminated polymer nanocomposite where the polymer component is confined at the nanoscale, achieving improved thermal-mechanical-electrical stability within the resulting nanocomposite. The nanolaminate, consisting of nanoconfined polyetherimide (PEI) polymer sandwiched between solid Al2O3 layers, exhibits a high energy density of 18.9 J/cm3 with a high energy efficiency of ~ 91% at elevated temperature of 200°C. Our work demonstrates that nanoconfinement of PEI polymer results in reduced diffusion coefficient and constrained thermal dynamics, leading to a remarkable increase of 37°C in glass-transition temperature compared to bulk PEI polymer. The combined effects of nanoconfinement and interfacial trapping within the nanolaminates synergistically contribute to improved electrical breakdown strength and enhanced energy storage performance across temperature range up to 250°C. By utilizing the flexible ultrathin nanolaminate on curved surfaces such as thin metal wires, we introduce an innovative concept that enables the creation of a highly efficient and compact metal-wired capacitor, achieving substantial capacitance despite the minimal device volume.

Alkyl chain length affecting the structure and interactions of choline-based amino acid ionic liquids: Insights from a computational study

The influences of the alkyl chain length of amino acid anions on the structure and interactions of choline-based amino acid ([Cho][AA]) ionic liquids were investigated based on density functional theory (DFT) and molecular dynamics (MD) simulations. The most stable configuration of the individual [Cho][AA] ion pair was determined, revealing negligible variations in the binding energy between choline cation ([Cho]+) and different amino acid anions ([AA]−). To further characterize the intermolecular interactions between charged entities, the atoms in molecules theory (AIM) and independent gradient model based on Hirshfeld partition (IGMH) were employed, which highlight the presence of robust hydrogen bonds between [Cho]+ and [AA] −, underscoring their significance in shaping the structure of [Cho][AA] ion pairs. The MD studies exhibited the aggregation of anions in [Cho][AA] ILs, which was attributed to side chain interactions of anions. This aggregation effect becomes more pronounced with the elongation of anionic alkyl chain. Simultaneously, radial distribution functions (RDF) analysis revealed a higher probability of hydrogen bonds occurring between [Cho]+ and [AA]− as the alkyl chain in [AA]− lengthened. Additionally, the hydrogen bond lifetimes roughly display an increasing trend as the alkyl chain of the [AA]− increases, which may be due to the reduced diffusion coefficients of ions. Hopefully, our results would contribute fundamental knowledge regarding the impact of alkyl chain length of anions on the structure and interactions in the choline-based amino acid ionic liquids.

Regions of Suppressed Diffusion around Supernova Remnants?

The recent discovery of the so-called TeV halos has attracted much attention. The morphology of the emission requires that the region is characterized by severe suppression of the diffusion coefficient. This finding raises many questions as to its origin: (1) is the suppressed diffusion to be attributed to instabilities induced by the same radiating particles? (2) or does it actually show that the diffusion coefficient is small throughout the disk of the Galaxy? In both cases, one would expect that the surroundings of supernova remnants (SNRs) should also show evidence of a reduced diffusion coefficient since most remnants are located in the disk and are expected to be sites of effective particle acceleration. Should we expect the existence of regions of extended γ-ray emission from these regions as well? Here, we investigate the transport of cosmic rays (CRs) that have escaped from SNRs in order to assess the viability of the idea of having a cocoon of suppressed diffusion around them. A comparison of our results with the γ-ray emission from the regions around HB9 and W28 does not provide solid evidence of reduced diffusivity. However, if indeed the phenomenon of reduced diffusivity occurs around SNRs surrounded by molecular clouds, our calculations show that the effects on the grammage of Galactic CRs can be significant.

Dynamic structure of E. coli cytoplasm: supramolecular complexes and cell aging impact spatial distribution and mobility of proteins

Protein diffusion is a critical factor governing the functioning and organization of a cell’s cytoplasm. In this study, we investigate the influence of (poly)ribosome distribution, cell aging, protein aggregation, and biomolecular condensate formation on protein mobility within the E. coli cytoplasm. We employ nanoscale single-molecule displacement mapping (SMdM) to determine the spatial distribution of the proteins and to meticulously track their diffusion. We show that the distribution of polysomes does not impact the lateral diffusion coefficients of proteins. However, the degradation of mRNA induced by rifampicin treatment leads to an increase in protein mobility within the cytoplasm. Additionally, we establish a significant correlation between cell aging, the asymmetric localization of protein aggregates and reduced diffusion coefficients at the cell poles. Notably, we observe variations in the hindrance of diffusion at the poles and the central nucleoid region for small and large proteins, and we reveal differences between the old and new pole of the cell. Collectively, our research highlights cellular processes and mechanisms responsible for spatially organizing the bacterial cytoplasm into domains with different structural features and apparent viscosity.

High-performance intrinsically stretchable organic solar cells based on flexible spacer incorporated dimerized small-molecule acceptors

High power conversion efficiency (PCE), long-term stability, and mechanical robustness are important requirements for the practical applications of organic solar cells (OSCs). Herein, we develop a series of flexible spacer (FS)-incorporated dimerized small-molecule acceptors (DSMAs; DYBT-C0, DYBT-C4, and DYBT-C8) and demonstrate high-performance OSCs with a high PCE of 18.6%, excellent mechanical robustness (crack-onset strain (COS) = 32%) and photostability (t80% lifetime = 1735 h under 1-sun illumination). The incorporation of aliphatic FS units with optimal length effectively reduces the backbone rigidity of the DSMAs and increases the fraction of intermixed domains in the blend films, while maintaining excellent electron transport properties. The DYBT-C4-based OSCs demonstrate higher PCE (18.6%) and stretchability (COS = 32%) compared to the OSCs based on the monomer acceptor (MYT; PCE = 15.9% and COS = 10%) and DSMA without FS units (DYBT-C0; PCE =17.2% and COS = 17%). In addition, due to the reduced diffusion coefficient and higher glass transition temperature of DYBT-C4, the DYBT-C4-based OSCs exhibit photostability significantly higher than that of the OSCs fabricated using MYT (t80% lifetime= 36 h). Consequently, DYBT-C4-based intrinsically stretchable (IS)-OSCs exhibit high device stretchability (strain at PCE80% = 36%) and PCE of 14.3%, demonstrating potential for wearable applications.

Micelles and structural variation of the solution synergistically changing the viscosity of sodium aluminate solutions

Complicated organic behavior in the sodium aluminate solution limits the economical alumina production and improvement in alumina quality by Bayer process. Sodium gluconate (SG) or sodium stearate (SS) in sodium aluminate solution containing sodium oxalate (SO) changed the interfacial occurrence of anionic organics. The single anionic organic compounds or mixed organics initially decreased and then raised the viscosity of the sodium aluminate solution, and further increasing total organic carbon (TOC) remarkably increased the viscosity of the industrial sodium aluminate solution. Correspondingly, increasing concentration of anionic organic compound raised initially and then reduced diffusion coefficient. The minimum viscosity of the solution nearly occurred at the critical micelle concentration (CMC) of the anionic organic compound. Anionic organics also increased the viscous flow activation energy of sodium aluminate solutions. The disordered structure of sodium aluminate solution reduced the viscosity and increased the diffusion coefficient at low concentrations of organics less than CMC. Further increasing the concentration of organic compound more than CMC, micelles then contributed to the ordered structure of the sodium aluminate solution, increasing viscosity and reducing the diffusion coefficient of the sodium aluminate solution. Therefore, a large amount of micelles and the different solution structures synergistically changed the viscosity and diffusion coefficient of the sodium aluminate solution.

MODELLING PARACRINE CHONDROCYTE COMMUNICATION EFFECTS AT THE TISSUE LEVEL

Osteoarthritis (OA) leads to articular cartilage degradation, following complex dysregulation of chondrocyte's metabolism towards a catabolic state. Mechanical and biochemical signals are involved and need to be considered to understand the condition. Regulatory network-based models (RNM) successfully simulated the biological activity of the chondrocyte and the transduction of mechanical signals at the molecular and cell levels. However, the knowledge gap between single-cell regulation and intercellular communication in tissue volumes hinders the interpretability of such models at larger scales. Accordingly, a novel tissue-level biochemical model is proposed. We hypothesise that it is possible to simulate interacting network effects through the transport of diluted species in a finite-element model, to grasp relevant dynamics of cell and tissue regulation in OA. Chondrocyte RNM equations were translated into a reaction term of 18 multi-species diffusion model (e.g., 3 anti-inflammatory and 8 pro-inflammatory interleukins, 3 pro-anabolic and 1 pro-catabolic growth factors, 2 nociceptive factors and 2 pro-inflammatory cytokines). Elements with RNM reaction terms represented the chondrocytes and were distributed randomly through the model, according to known cellular density in the knee cartilage, and could both react to and produce diffusive entities through the pericellular matrix, associated with reduced diffusion coefficients. The model was constructed over a 2D square of 0.47 mm sides considered to be in the middle of the cartilage, so boundary conditions were settled as periodic. Different simulations were initialised with initial concentrations of either healthy or pro-OA mediators. Preliminary results showed that, independently of the initial conditions, the chondrocytes successfully evolved into anabolic states, in absence of sustained pro-catabolic external stimulations, in contrast to single-cell RNM [2]. Our intercellular model suggests that paracrine communication may increase robustness towards cartilage maintenance, and future tests shall reveal new OA dynamics.Acknowledgements: Funding was provided by the European Commission (ERC-2021-CoG-O-Health-101044828).

Water behavior at PEMFC triple phase boundary: Exploring ionomer and catalytic layer effects via molecular dynamic simulations and NMR experiments

Polymer electrolyte membrane fuel cells (PEMFCs) offer a clean and efficient energy generation technology. However, optimizing their performance in terms of water transport through the electrolyte membrane remains a challenge. In this study, we employ molecular dynamics simulation and nuclear magnetic resonance (NMR) experiments to investigate the influence of carbon materials and membrane thickness on water diffusion within the triple phase boundary of a PEMFC. Our theoretical investigation highlights the significant impact of Nafion content on water morphology within the system. The structural analysis reveals the intricate interplay between material properties and water behavior in confined environments. The formation of water channels facilitated by the ionomer enhances water mobility, while excessive ionomer content leads to reduced diffusion coefficients. Experimental measurements using NMR diffusion validate the correlation between our simulation results and real-world observations. Furthermore, our Molecular Dynamic (MD) and NMR studies identify the optimal performance range for ionomer content, with systems containing 12 to 24 oligomers (20–30 % w/w) exhibiting superior water diffusion within Vulcan Carbon (VC) structures. By shedding light on water transport phenomena in PEMFCs, our findings contribute to a better understanding of fuel cell performance and provide valuable insights for the design and optimization of fuel cell systems.

Diffusion and viscosity coefficient in Lennard-Jones fluids: excess entropy scaling law

We investigated the proportional relationship between the diffusion coefficient and the viscosity coefficient and excess entropy in Lennard-Jones fluids. Based on the theoretical basis of Dzugutov and Bell et al., we came up with a new expression. Using molecular dynamics simulation to calculate the radial distribution function (RDF), the reduced diffusion coefficient D* and the reduced shear viscosity coefficient η* in the state of reduced density ρ* = 0.5 and the reduced temperature range of 1 ≤ T* ≤ 2.8. The two body excess entropy S2 was calculated from RDF. The results showed that the reduced diffusion coefficient and the reduced viscosity coefficient and the excess entropy present the exponential scaling behaviour. Our results supported the notion put forth by Dzugutov and Bell et al. but had different adjust parameters. The dependence of the reduced diffusion coefficient on the reduced temperature are also explored, they qualitatively exhibited a 2/3 power function relationship. In addition, we have quantitatively calculated the relation schema of ln(η*)-ln(D*/T*) in Lennard-Jones fluids that with LJ potential (n = 12) without considering the influence of the packing fraction and found that the reduced diffusion coefficient and reduced viscosity satisfy the new Stokes–Einstein relationship proposed by Ohtori et al.

Modifying the microstructure and stress distribution of crossover Al-Mg-Zn alloy for regulating stress corrosion cracking via retrogression and re-aging treatment

For next-generation high-performance Al alloys, stress corrosion cracking (SCC) under the combined action of anodic dissolution and hydrogen embrittlement has been a long-standing problem. Herein, a novel SCC-resistant Al alloy design strategy that maintains high strength by optimizing the microstructure and microstress distribution is proposed and developed. Results demonstrated that stress corrosion cracks sprouted and expanded along stress concentration regions. In a T-phase strengthened crossover Al–5.0Mg–4.0Zn alloy, minimal stress concentrations at the grain and phase boundary improved the SCC resistance by high-temperature retrogression and re-aging treatments. Compared with the T6 alloy, the high-temperature retrogression RRA435 °C alloy reduced stress concentration by 36.7% and decreased the diffusion rate of H atoms by 81 folds. The improved SCC resistance was primarily attributed to the reduced diffusion coefficient of hydrogen because of the minimal stress concentrations.

An Elucidative Review of the Nanomaterial Effect on the Durability and Calcium-Silicate-Hydrate (C-S-H) Gel Development of Concrete.

Concrete as a building material is susceptible to degradation by environmental threats such as thermal diffusion, acid and sulphate infiltration, and chloride penetration. Hence, the inclusion of nanomaterials in concrete has a positive effect in terms of promoting its mechanical strength and durability performance, as well as resulting in energy savings due to reduced cement consumption in concrete production. This review article discussed the novel advances in research regarding C-S-H gel promotion and concrete durability improvement using nanomaterials. Basically, this review deals with topics relevant to the influence of nanomaterials on concrete's resistance to heat, acid, sulphate, chlorides, and wear deterioration, as well as the impact on concrete microstructure and chemical bonding. The significance of this review is a critical discussion on the cementation mechanism of nanoparticles in enhancing durability properties owing to their nanofiller effect, pozzolanic reactivity, and nucleation effect. The utilization of nanoparticles enhanced the hydrolysis of cement, leading to a rise in the production of C-S-H gel. Consequently, this improvement in concrete microstructure led to a reduction in the number of capillary pores and pore connectivity, thereby improving the concrete's water resistance. Microstructural and chemical evidence obtained using SEM and XRD indicated that nanomaterials facilitated the formation of cement gel either by reacting pozzolanically with portlandite to generate more C-S-H gel or by functioning as nucleation sites. Due to an increased rate of C-S-H gel formation, concrete enhanced with nanoparticles exhibited greater durability against heat damage, external attack by acids and sulphates, chloride diffusion, and surface abrasion. The durability improvement following nanomaterial incorporation into concrete can be summarised as enhanced residual mechanical strength, reduced concrete mass loss, reduced diffusion coefficients for thermal and chloride, improved performance against sulphates and acid attack, and increased surface resistance to abrasion.

Kinetic and Thermodynamic Properties of Ytterbium Chloride and Fluoride Complexes in Chloride Melts

The electrochemical behavior of trichloride ytterbium in NaCl-KCl, KCl, and CsCl melts was studied in the temperature range 973–1173 K by different electrochemical methods. The diffusion coefficients (D) of Yb(III) and Yb(II) were determined by linear sweep voltammetry, chronopotentiometry and chronoamperometry methods. The standard rate constants of charge transfer (k s) for the Yb(III)/Yb(II) redox couple were calculated on the basis of cyclic voltammetry data using Nicholson’s equation. The formal redox potentials E * Yb(III)/Yb(II) in alkali chloride melts were obtained by the cyclic voltammetry and the Gibbs free energy for the reaction: YbCl2(sol.) + 1/2 Cl2(g.) ↔YbCl3(sol.) in alkali chloride melts was calculated. The electrochemical behavior of the Yb(III)/Yb(II) redox couple in the NaCl-KCl- NaF (5 wt%) melt was studied. A comparative analysis of electrochemical behavior of ytterbium chloride complexes in the NaCl-KCl melt and ytterbium fluoride complexes in the NaCl-KCl- NaF (5 wt%) melt was performed. It was shown that the formation of the stronger fluoride complexes reduced diffusion coefficients, standard rate constants of charge transfer for the Yb(III)/Yb(II) redox couple, and shifted the formal standard redox potentials to more electronegative values.

Quantum localization corrections from the Bethe–Salpeter equation

We investigate coherent matter wave transport in isotropic 3D speckle potentials by using the Bethe–Salpeter equation and the self-consistent theory of localization. This model constitutes an efficient tool to properly evaluate corrections to Boltzmann diffusion by taking into consideration quantum interference terms between the multiple-scattering paths. We calculate analytically and numerically the static current density, the density of states, the dipolar contribution and the reduced diffusion coefficient. Our results reveal that quantum corrections to diffusive transport, known as weak localization may not only lead to shift the above quantities but affect also the position of the mobility edge.

Bijels as a Fluid Labyrinth for Drugs: The Effect of Nanoparticles on the Release Kinetics of Ethosuximide and Dimethyl Fumarate.

Bijels (bicontinuous interfacially jammed emulsion gels) raised an increasing interest as biomaterials for controlled drug delivery due to their biphasic nature organized in mesoscopic tortuous domains. Two bijel formulations were prepared and explored as delivery systems for both hydrophilic and lipophilic drugs, ethosuximide and dimethyl fumarate. The two bijel-like structures, based on polymerized ε-caprolactone/water, differ in the stabilizing nanoparticle hydroxyapatite (inorganic) and nanogel-based nanoparticles (organic). Diffusion nuclear magnetic resonance spectroscopy has been used to characterize the bijel structure and the transport behavior of the drug molecules confined within the water/organic interconnected domains. A reduced diffusion coefficient is observed for several concentrations of the drugs and both bijel formulations. Moreover, in vitro release profiles also reveal the effect of the microstructure and drug-nanoparticle interactions.

Walker breakdown of Brownian domain wall dynamics

The Brownian motion of domain walls in uniaxial and biaxial ferromagnetic nanowires is studied, comparing spin dynamics simulations with analytical calculations within the framework of a collective coordinate approach. Our results demonstrate that the interplay between spatial and angular dynamics gives rise to a complex time dependence of the MSD in biaxial nanowires and to a drastically reduced diffusion coefficient in uniaxial nanowires, analogous to magnetic skyrmions. This diffusion suppression is also responsible for the peculiar temperature dependence of the diffusion coefficient in biaxial systems: while it is found to scale linearly with temperature up to a certain threshold, the emergence of a Walker breakdown of Brownian motion is responsible for a reduction of the diffusion coefficient with increasing temperature above this threshold.

Modeling pyramidal silicon nanopores with effective ion transport

While the electrical models of the membrane-based solid-state nanopores have been well established, silicon-based pyramidal nanopores cannot apply these models due to two distinctive features. One is its 35.3° half cone angle, which brings additional resistance to the moving ions inside the nanopore. The other is its rectangular entrance, which makes calculating the access conductance challenging. Here, we proposed and validated an effective transport model (ETM) for silicon-based pyramidal nanopores by introducing effective conductivity. The impact of half cone angle can be described equivalently using a reduced diffusion coefficient (effective diffusion coefficient). Because the decrease of diffusion coefficient results in a smaller conductivity, effective conductivity is used for the calculation of bulk conductance in ETM. In the classical model, intrinsic conductivity is used. We used the top-down fabrication method for generating the pyramidal silicon nanopores to test the proposed model. Compared with the large error (≥25% in most cases) when using the classical model, the error of ETM in predicting conductance is less than 15%. We also found that the ETM is applicable when the ratio of excess ion concentration and bulk ion concentration is smaller than 0.2. At last, it is proved that ETM can estimate the tip size of pyramidal silicon nanopore. We believe the ETM would provide an improved method for evaluating the pyramidal silicon nanopores.

Drug diffusion in biomimetic hydrogels: importance for drug transport and delivery in non-vascular tumor tissue

Hydrogels of varying complexity are routinely used as scaffolds and 3D structures for in vitro tumor models to increase physiological relevance within pre-clinical cancer research. Relatively simple hydrogels such as agarose are well characterised, meanwhile biomimetic gels containing collagen and fibrin(ogen) have been studied to a much lesser extent. In this study, hydrogels mimicking the biophysical characteristics of liver cancer progression were investigated in terms of their UV-properties and influence on diffusion coefficients of different substances. UV-imaging technology was used to both visualize and quantify the diffusion process in a simple and rapid way. In general, agarose gel diffusion agreed well with predictions using the Stokes-Einstein equation meanwhile the biomimetic gels reduced diffusion coefficients by up to 70%. For doxorubicin, spatio-temporal tissue concentration modelling was used to translate in vitro diffusion to the more clinical context of tumor penetration in a solid liver tumor supplied by arterial blood.

Molecular diffusion in gases and liquids

The diffusion coefficients in gases and liquids calculated by the molecular dynamics method with the use of the hard absolutely rough elastic spheres model are compared with those calculated using the Lennard-Jones potential. It is shown that dependences of reduced diffusion coefficients on density are similar, but differ numerically for different intermolecular interaction models. The simulation results have been compared with the experimental data on the diffusion in gaseous and liquid argon and in liquid benzene.

Simulating diffusion in the conditions of vapor-liquid phase transition by the molecular dynamics method

The molecular dynamics calculations of diffusion coefficients in binary Lennard-Jones systems have been carried out. The parameters of Lennard-Jones potentials correspond to argon and krypton atoms. The universal dependence of the reduced diffusion coefficient of krypton atoms on density for the homogeneous systems of low and middle densities is found. The deviations of the diffusion coefficients from the universal function are observed for the systems in the vapor – liquid phase transition region. The simulations have shown that almost all krypton atoms have situated inside the liquid phase of argon. Special numerical experiments have shown that the nanodroplets of argon are formed as a result of homogeneous nucleation and then the krypton atoms are captured by these droplets. This phenomenon decreases the diffusion coefficient of krypton atoms greatly.

Non-Exponential 1H and 2H NMR Relaxation and Self-Diffusion in Asphaltene-Maltene Solutions.

The distribution of NMR relaxation times and diffusion coefficients in crude oils results from the vast number of different chemical species. In addition, the presence of asphaltenes provides different relaxation environments for the maltenes, generated by steric hindrance in the asphaltene aggregates and possibly by the spatial distribution of radicals. Since the dynamics of the maltenes is further modified by the interactions between maltenes and asphaltenes, these interactions—either through steric hindrances or promoted by aromatic-aromatic interactions—are of particular interest. Here, we aim at investigating the interaction between individual protonic and deuterated maltene species of different molecular size and aromaticity and the asphaltene macroaggregates by comparing the maltenes’ NMR relaxation ( and ) and translational diffusion (D) properties in the absence and presence of the asphaltene in model solutions. The ratio of the average transverse and longitudinal relaxation rates, describing the non-exponential relaxation of the maltenes in the presence of the asphaltene, and its variation with respect to the asphaltene-free solutions are discussed. The relaxation experiments reveal an apparent slowing down of the maltenes’ dynamics in the presence of asphaltenes, which differs between the individual maltenes. While for single-chained alkylbenzenes, a plateau of the relaxation rate ratio was found for long aliphatic chains, no impact of the maltenes’ aromaticity on the maltene–asphaltene interaction was unambiguously found. In contrast, the reduced diffusion coefficients of the maltenes in presence of the asphaltenes differ little and are attributed to the overall increased viscosity.