Fractional Free Volume Research Articles

Assessment of water diffusion in epoxy composites: a novel approach towards holistic understanding

Performance of insulating polymers is seriously impacted by water absorption. Hence, its assessment using Fick’s law and 3-core water shell model are used for a holistic understanding of water diffusion. Epoxy with organically modified montmorillonite clay of 2, 5 and 7 weight percent (wt.%) are fabricated and water diffusion is carried out for 240 hours. The results are analysed by dielectric and gravimetric approaches. The weight gain in epoxy after 240 hours is 0.42% and 0.19% at 5 wt.% of the filler. The weight gain peaks after 120 hours in all the composites and the variations from 120 to 240 hours are minimal. The weight gain rate is lowest at 96 hours, and it peaks at 120 hours and is highest at 0.00033%/hour in epoxy, and reduces to 0.0023%/hour with filler of 7 wt.%. The weight gain and weight gain rate are characteristics of the epoxy and the filler controls the magnitude. Diffusion coefficient is lowest at 5 wt.% but the differences in the other composites are limited. The effect of fillers on free volume, free volume rate and fractional free volume are correlated to the dielectric parameters. Water uptake increases the DC conductivity from 10−14 to 10−12 S/m after 240 hours and the relative permittivity increases by 40%. The water shell model, diffusion parameters and the free volume parameters are correlated to the results of DC conductivity and relative permittivity. Subtle changes induced by absorbed water is identified by the method adopted.

High‐Performance and Scalable Organosilicon Membranes for Energy‐Efficient Alcohol Purification

AbstractThe production of bio‐alcohol is increasingly gaining international attention due to its potential as a viable alternative to fossil fuels and its ability to mitigate carbon dioxide emissions. However, the cost of bio‐alcohol production is almost double that of fossil fuels, primarily because of the low yield of the purification process. Herein, a high‐performance and scalable organosilicon membrane with high chain flexibility and controllable crosslinking density is developed for energy‐efficient alcohol purification. The synthesized organosilicon membrane achieves an ultrahigh total flux (5.8 kg·m−2·h−1) with a comparable separation factor (8.7) for ethanol/water separation, outperforming most state‐of‐the‐art polymer‐based membranes. Integrated experiments and molecular dynamics simulations confirm that the ultrafast alcohol permeation of the membrane originates from its high chain flexibility, large fractional free volume, and weak interactions between feed molecules and membranes. The universal applicability of the low‐crosslinking mechanism for the formation of high‐performance organosilicon membranes is also validated. Moreover, its high efficiency and scalability in membrane production, along with the stability of the casting solution, offer promising prospects for industrial applications.

Modified boron nitride reinforced natural rubber composites and molecular dynamics simulation

AbstractFor thermal conductive boron nitride (BN)/polymer composites, an overabundance of BN in the formulation may significantly impair the mechanical integrity, thereby restricting their applicability in practical scenarios. In this work, we introduced a novel modifying agent, which was grafted onto the exterior of BN following high‐temperature calcination. The resultant modified boron nitride demonstrated a marked improvement in the thermal conductivity and mechanical characteristics of natural rubber (NR) composites. Upon incorporating a filler content of 60 phr, the modified boron nitride NR composite achieved tensile strength, elongation at break, and thermal conductivity to 19.34 MPa, 1402%, and 0.735 W/mK, respectively, which represented an increase of 23.97%, 75.69%, and 33.15% over the BN/NR composite. The observed enhancement in mechanical properties and thermal conductivity of the composites is the contribution of the novel modifier grafting on the BN surface, which has notably improved the interfacial interaction with NR. In addition, the binding energy, solubility parameter, free volume fraction, and radial distribution function of BN/NR and modified boron nitride NR composites were analyzed by molecular dynamics simulation, which provided support for the interface reinforcement mechanism. This simple and versatile modification method introduced in this work can broaden prospects in the design of natural rubber composites.Highlights Successful synthesized of a new modifier with long chains. Interfacial compatibility of composites explained by combining molecular dynamics simulations. Effectively improved both the mechanical and thermal conductivity of the composites. Successful use of high‐temperature assisted modification to graft modifiers onto BN surfaces.

Quantification of physical aging using two MDSC methods and its effect on initial properties of epoxy films

In this work, the effect of aging times and temperatures on the generation of physical aging (P.A) is investigated, as well as its impact on the physico-chemical and mechanical properties of a model epoxy resin. The DGEBA/Jeffamine D230 system was tested with different amounts of P.A generated by applying steps of varying aging times and temperatures during the cooling. The quantification of P.A is carried out through modulated differential scanning calorimetry (MDSC) using two methods, based on the heat flow or the non-reversing heat flow. The results show that the P.A values obtained with the first method are lower than those obtained by the second method. The theorical model of Kohlrausch-Williams-Watts, used to describe the kinetic behavior of P.A process, showed that the second method underestimates the relaxation time. If no chemical change was observed between systems with and without P.A, the thermo-mechanical analysis showed that physical aging induces a storage modulus increase together with a free volume fraction decrease.

Microscopic effect and mechanism of spray polyurea modifier on the asphalt binder: Experimental characterization and molecular dynamics simulations

To investigate the impact of spray polyurea (SPUA) modifiers on the microstructure and performance of asphalt, SPUA powder prepared by cryogenic grinding was selected as modifier to explore the microscopic mechanisms of spray polyurea modified asphalt. Initially, the morphological characteristics of the SPUA modifiers were systematically characterized using morphological methods. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were conducted to examine the effects of SPUA on the thermodynamic properties of asphalt. Finally, molecular dynamics simulations were utilized to model SPUA modified asphalt at different concentrations. Critical parameters such as cohesive energy density, solubility parameters, interaction energy, free volume, and radial distribution function (RDF) were analyzed to elucidate the microscopic mechanisms underlying the experimental results. The results indicate that the surface morphology of SPUA includes several pore structures, which enhance the tight and continuous bonding at the SPUA asphalt interface, thereby enhancing the microstructural stability of the modified asphalt. Additionally, incorporating SPUA increased the decomposition temperature of the asphalt binder, improving its thermal stability. This phenomenon is further validated by molecular dynamics simulations, which show that with increasing amounts of polyurethane, both the cohesive energy density and interaction energy of the asphalt system significantly increase, thereby enhancing the structural strength of the asphalt system. However, while low SPUA concentrations enhance the surface roughness of the asphalt, excessive SPUA may disrupt the uniform dispersion of the asphalt binder. This leads to a reduction in the difference in solubility parameters between the two components, diminishing compatibility, and decreasing the free volume fraction of the asphalt while increasing the peak of the radial distribution function curve. Such changes adversely affect the flowability and stability of the modified asphalt.

Effects of carbon nanotube and alumina doping on the properties of para-aramids: A DFT and molecular dynamics study

Because of its superior mechanical and electrical insulation qualities, paramamid insulating paper is frequently used in the electrical industry. However, a significant barrier preventing it from taking a more prominent role is its low heat conductivity. This research modifies aramid by doping it with carbon nanotubes and alumina to balance its insulating qualities and increase its thermal conductivity. Materials Studio uses molecular dynamics (MD) computations to examine the thermodynamic parameters of the composite system, such as modulus, glass transition temperature, and thermal conductivity. the system's cohesive energy density, free volume fraction, mean square displacement, and other structural characteristics. The relative dielectric constant is used to calculate the insulating characteristics. The Density Functional Theory (DFT) is then used to calculate the fluctuation of the electrostatic potential with Mulliken charge on the electrical properties. According to the findings, a single doped carbon nanotube significantly raises its mechanical and thermal conductivity while completely destroying its insulation. While single alumina doping increases the insulating properties of the system and yields improved structural parameters and tighter intermolecular bonding, it has minimally positive effects on its thermal conductivity. When mixed doping is used, the system's thermodynamics will be significantly enhanced without compromising its insulating qualities.

The influence of diamine structure on low dielectric constant and comprehensive properties of fluorinated polyimide films

Three kinds of polyimide (PI) films with low dielectric constant and excellent comprehensive properties were prepared by polycondensation reaction employing 6FDA as the dianhydride monomer and 6FODA, TFMB and 6FDAM as the diamine monomers, respectively. The effects of diamine moieties on the low dielectric constant and comprehensive properties were investigated by experiments and theoretical simulations. All three PI films show excellent high temperature resistance. For instance, the 5 % weight loss temperature ranges from 495 to 511 °C, and the Tg from 305.5 to 347.2 °C. 6FDA/6FODA exhibits a higher dielectric constant (k) compared with the other two PIs because of low free volume fraction and low rotating energy barrier of torsion angle for 6FODA moieties. 6FDA/TFMB exhibits ultra-low k (1.84 at 104 Hz) being benefit from its high free volume fraction caused by the strong rigidity of molecular chain. Despite having the highest free volume fraction among the three PIs, 6FDA/6FDAM exhibits a slightly higher dielectric constant than 6FDA/TMFB due to the fact that the torsion angle for 6FDAM moieties has low rotating energy barrier, which is beneficial for improving the molecular polarizability. Meanwhile, all the PI films show excellent transparency in the visible light range as well as excellent mechanical properties. The results indicate that the microstructure of PI can be effectively adjusted, thus achieving an ultra-low k and excellent comprehensive properties by rationally designed diamine moiety.

Quaternized poly(aryl imidazolium) containing bulky binaphthyl group as proton exchange membrane for high-temperature fuel cells

The low power output and high phosphoric acid (PA) leakage are the main constraints restricting the commercialization of PA-doped high-temperature proton exchange membranes (HT-PEMs). Ionized imidazoles have been shown to be an effective strategy to improve PA retention, however, less research has been conducted on the fractional free volume (FFV) of the backbone of the main chain on PA loss. Herein, novel imidazolium ions polymer (PQBN-4-IM) material with bulky binaphthyl (BN) group was prepared as PA-doped HT-PEM using a one-step superoxid acid catalyzed polycondensation and subsequent methylation process. The rigidity and hydrophobicity of the BN group promote PQBN-4-IM PEM to produce more obvious microphase separation morphology and large FFV, which is beneficial for forming better ion transport channels and excellent PA interaction. Notably, the PA-doped PQBN-4-IM (PQBN-4-IM/PA) membrane has the highest proton conductivity (90.26 mS cm−1, 180 ℃) and peak power density (PPD) (802.5 mW cm−2, 180 ℃) than PQTP-4-IM/PA and m-PBI/PA HT-PEMs. Moreover, the PQBN-4-IM/PA membrane has higher PA retention at 80 ℃/40 % relative humidity (RH), 40 ℃/60 % RH, or immersed in water due to enhancement on ion-pair interactions by microstructure. Under the accelerated stress test (AST) of the fuel cell (FC), the PQBN-4-IM/PA membrane loses only 12.22 % of PPD after 200 cycles at 80 ℃, which exhibits higher PPD retention than that of the PQBP-4-IM/PA (70.23 %), PQTP-4-IM/PA (74.36 %) and m-PBI/PA (65.25 %) membranes, and shows excellent durability of cell performance for more than 1000 h without significant voltage decay at 160 °C. Thus, the outstanding performance suggests that the microstructure and morphology of imidazolium ions polymer membranes significantly influence proton conductivity, performance, and the durability of a cell.

Mainchain and sidechain-involving H-bonded asymmetric polyimides containing rigid amide and flexible ether linkages

Hydrogen bonds (H-bonds), usually mainchain amide H-bonds, have been well recognized to play important roles in modulating the properties of polyimides (PIs) by strengthening macromolecular interaction. While the structure-properties relationships of symmetric mainchain amide H-bonded PIs have been extensively researched, the asymmetric H-bonded PIs, particularly those containing rigid-flexible backbone structure, and sidechain-involving H-bonds, have been rarely explored. Herein, starting from designed synthesis of diamine monomers, we present two series of asymmetric PIs containing rigid amide and flexible ether linkages that form mainchain amide-amide and amide-imide H-bonds, lacking or bearing pendent trifluoromethyls (-CF3) that form sidechain-involving amide-CF3 H-bonds. The presence of these three types of H-bonds were revealed by RDF simulation and confirmed by FTIR. Mainchain H-bonded PIs (PI-Ax) show higher Tg than sidechain-involving H-bonded PIs (PI-Tx), while PI-Tx series exhibit higher optical transparency and hydrophobicity, lower dielectric constant (ε′) and better mechanical properties than PI-Ax. The general researches on the PIs’ solubility, WAXD spectra, thermal properties, fluorescence emission and optical transparency, the dihedral angles (φ), fractional free volume (FFV), theoretical gas transport properties, chain geometry optimization and HOMO-LUMO energy gap (ΔE) values have been comprehensively carried out from the aspects of both experiments and theoretical calculation.

Interaction and Diffusion Mechanism of Moisture in Power Capacitor Insulating Oil Based on Molecular Simulation.

Characterized by its exceptional electrical, physical, and chemical properties, 1-phenyl-1-xylylethane (PXE) insulating oil finds extensive application in the realm of power capacitor insulation. In this study, molecular simulation is employed to investigate the reactivity of PXE insulating oil molecules and the impact of temperature on water diffusion behavior in PXE insulating oil, as well as its solubility. The findings demonstrate a higher propensity for hydrogen atoms in nucleophilic and electrophilic positions within PXE insulating oil molecules to interact with water molecules. The inclusion of a temperature field enhances the Brownian motion of water molecules and improves their diffusion ability within the oil. Furthermore, the temperature field diminishes the interaction force between water molecules and the oil medium. Under the influence of this temperature field, there is an increase in the free volume fraction of PXE insulating oil, leading to a weakening effect on hydrogen bonds between oxygen and hydrogen atoms within PXE insulating oil. Additionally, with increasing temperature, there is an elevation in moisture solubility within insulating oil, resulting in a transition from a suspended state to a dissolved state.

Engineering designed functional covalent organic frameworks via pore surface modifications for effectively reducing the dielectric constant of polyimide-based electronic packaging materials

Polyimide (PI) is considered one of the most promising candidate materials for the microelectronics and wireless communication industries. Nevertheless, the relatively high dielectric constant of PI has become a significant obstacle, constraining its utilization in the realm of microelectronics. Herein, novel PI nanocomposite films were fabricated by incorporating covalent organic frameworks (COFs) and their functionalized counterparts (COF@POSS and COF@DTF) through post-synthetic modification. Among all PI nanocomposites films, PI/COF@POSS nanocomposite film including 2 wt% COF@POSS achieved the lowest dielectric constant (2.41) and dielectric loss (0.0076). These values represented a reduction of 22.5 % and 24 % compared to pure PI, respectively. The decrease in dielectric constant is ascribed to the combined influence of the porous structure of COF and the augmentation in free volume fraction caused by the steric hindrance of POSS. Additionally, the tensile strength of the PI/COF@POSS and PI/COF@DTF nanocomposite films increased up to 121.1 MPa and 112.0 MPa, representing a 95 % and 80 % improvement over pure PI, respectively. Furthermore, the introduction of COFs functionalized with POSS and DTF significantly enhanced the hydrophobicity of PI nanocomposite films. The combination of porous organic nanofillers with surface functionalization offers a feasible route to create low-k PI nanocomposite films with improved mechanical properties and hydrophobicity.

Computational insights into pectin and chitosan-enhanced MOFs: A green pathway for pollutant remediation

Water contamination with dyes and pharmaceuticals is a major threat to ecological and human well-being. This study highlights the importance of using molecular simulations in designing and predicting the performance of novel adsorbents for wastewater treatment. The research explores the potential of biodegradable polymers like Pectin (PE) and oxidized Chitosan (OCN) in functionalizing a metal-organic framework (MOF) known as UO-66 (Zr) (UO). By incorporating these functional groups, the study aims to improve the adsorption efficiency of UO towards rhodamine B (RHOB, a dye pollutant) and Losartan (LOSA, a pharmaceutical pollutant). Firstly, density functional theory (DFT) calculations were employed to inspect the structures of both pollutants and the modified adsorbents. Subsequently, the research investigated the adsorbents’ various physicochemical characteristics, including fractional free volume, glass transition temperature, and mechanical properties. Finally, molecular dynamics (MD) and Monte Carlo (MC) simulations were accomplished to evaluate the adsorption behaviour of the pollutants on various UO forms (pristine, PE-functionalized, and OCN-functionalized). The study found that all adsorbents showed strong adsorption capabilities, with adsorption energies ranging from −3500 to −4500 kcal/mol for RHOB and −1500 to −2600 kcal/mol for LOSA. Moreover, The drug rejection rate of RHOB for neat is 50 % but increases to 80 % and 90 % with the addition of PE and OCN, respectively, showing their synergistic effect. Similarly, the accumulation rate rises from 6 Å (NH2/UO) to 10 Å (OCN/UO) and 11 Å (PE/UO). For LOSA, the drug rejection rate improves from 30 % to 60 %, while the accumulation rate increases from 4 Å to 8 Å with PE and OCN functionalization. The results demonstrated that functionalizing UO with the chosen biodegradable polymers enhanced its adsorption capacity for both pollutants compared to the pristine form. Notably, the developed adsorbent exhibited a higher affinity towards RHOB dye compared to LOSA pharmaceutical.

Exploring the potential of beta-cyclodextrin-based MIL-101(Cr) for pharmaceutical removal from wastewater: A combined density functional theory and molecular simulations study

Pharmaceutical contaminants pose significant risks to ecosystems and human health, necessitating effective removal strategies. This research focuses on developing advanced adsorbents for removing pharmaceutical pollutants from the environment. Metal-organic frameworks (MOFs), specifically MIL-101(Cr) functionalized with biodegradable beta-cyclodextrin (β-CDex), were investigated as potential nanocomposite adsorbents for the removal of ketorolac (KTRK), naproxen (NPXN), and tramadol (TRML). The study employed molecular simulations and density functional theory (DFT) calculations to explore the interactions between the pollutants and adsorbents. Analyses of DFT results, including electrostatic potential, ionization energy, density of states, and molecular orbital analysis, provided insights into the reactivity of pollutants and adsorbents. Additionally, the structural properties of the adsorbents, such as fractional free volume, radius of gyration, and system energies, were thoroughly examined. Molecular dynamics (MD) and Monte Carlo (MC) simulations were used to evaluate the adsorption capacities of MIL-101(Cr) for the target pharmaceutical pollutants. The results demonstrated the superior adsorption performance of the nanocomposite adsorbent, particularly for KTRK, with an adsorption energy of −1934 kcal/mol, compared to the pristine MIL-101(Cr), which had an adsorption energy of −1916 kcal/mol. This enhanced adsorption is attributed to the optimal molecular fit, guest-host solid interactions, and the selective encapsulation capabilities of β-CDex. This research highlights the potential of MOF-based nanocomposites as effective and sustainable solutions for pharmaceutical pollution. By advancing the understanding of molecular interactions through simulations, this study contributes to developing innovative adsorbents for wastewater treatment and the protection of water resources.

Molecular insights of DGEBA/MeTHPA three-dimensional resin network from design to heat transfer mechanism: Dynamic simulation and experimental research

The epoxy resin composed of bisphenol A diglycidyl ether (DGEBA) and methyl tetrahydrophthalic anhydride (MeTHPA) has been found to enhance its thermal conductivity by increasing its molecular weight and crosslinking density. This was achieved through experiments and all-atom molecular dynamics simulations. Molecular dynamics was employed to calculate the root-mean-square displacement, free volume fraction, potential energy, density, and quantity of hydrogen bonds. The results showed the influence of molecular weight and crosslinking density on the system's thermal conductivity. The results showed that the high molecular weight epoxy resin system exhibited high thermal conductivity at elevated crosslinking densities. During the crosslinking process, the epoxy resin's thermal conductivity increased, starting with the center portion weakening and then strengthening. In addition, a simulation-verified free volume was found to have an inversely proportional connection with thermal conductivity. This study explored the thermal conductivity mechanism of epoxy resin by analyzing the structural changes at the micro level and correlating them with the changes in thermal conductivity at the macro level to enhance guidance for industrial production and practical application.

Correlation of proton conductivity and free volume in sulfonated polyether ether ketone electrolytes: A positron annihilation lifetime spectroscopy study

Proton-conducting polymers play a pivotal role in clean energy technologies and various industrial applications, with a significant emphasis on enhancing energy efficiency and minimizing environmental impact. Sulfonated polyether ether ketone (SPEEK), which is renowned for its proton conductivity, has emerged as a key material in electrochemical processes, notably in proton exchange membrane (PEM) fuel cells. This study investigated the proton conductivity and dielectric behavior of SPEEK electrolytes at varying degree of sulfonation (DS) of 65% and 80%, correlating these properties with free volume profiles determined by positron annihilation lifetime spectroscopy (PALS). The SPEEK-65 and SPEEK-80 electrolytes were prepared via a controlled sulfonation process and characterized by FTIR, TGA, and SEM analyses. Proton conductivity and dielectric measurements were conducted at temperatures ranging from 300 to 370 K and frequencies ranging from 20 Hz to 1 MHz. The results revealed that SPEEK-80 exhibited a maximum proton conductivity of 3.4 × 10−2 S/m at 300 K and 1 MHz, which was significantly greater than the 4.38 × 10−3 S/m observed for SPEEK-65 under the same conditions. PALS analysis demonstrated a notable increase in free volume with increasing DS, with SPEEK-80 showing a higher o-Ps lifetime and intensity, indicating larger free volume sizes and fractions. These findings underscore the critical interplay between DS, free volume, and proton conductivity, offering insights into optimizing SPEEK-based electrolytes for advanced electrochemical applications.

Chain relaxation of carborane segments with tailored chain length at high temperatures

High-performance thermoset polymers have good thermal stability due to their highly crosslinked network, while also represent topological constraints that restrict cooperative segmental motion, making it difficult to relax stresses even at high temperatures. Failure of most thermoset polymers at high temperatures is due to ineffective stress relaxation, which limits the use of thermoset polymers in harsh environments. Herein, we employed a cyclosiloxane hybrid polymer (CHP) containing o-carborane segments with tailored carbon chain length to relieve internal stress. The introduction of o-carborane and lengthening of carbon chain both increased the CHP fractional free volume, and reduced the activation energy required in the later stages of the curing process. The carbon chain changed the conformation to achieve chain relaxation by stretching and rotating the carbon–carbon bonds at high temperatures, which avoided cracking and increased the failure temperature of the CHP. Furthermore, the adhesion strength of the o-carborane modified CHP reached a maximum of 2.15 MPa, surpassing 1.23 MPa of the neat CHP. The o-carborane modified CHP with the longest carbon chain exhibited good stability while supporting 1 kg load for 5 min when subjected to ablation, whereas the neat CHP failed after only 47 s. The o-carborane-modified CHP exhibited enhanced high-temperature properties through chain relaxation to inhibit cracking and in situ generation of boron oxide at high temperatures to protect the resin matrix.

Composition-dependent diffusion and viscosity behavior in liquid Ti–Al–Ni ternary alloys

We conducted ab initio molecular dynamics simulations to investigate the dynamic properties of the liquid Ti–Al–Ni ternary alloy system at 2033 K. Through simulations across the entire composition range, we revealed the complex compositional dependence of self-diffusion coefficients and viscosity. The self-diffusion coefficients of Ti, Al, and Ni exhibit nonlinear distribution characteristics, while viscosity shows non-monotonic compositional dependence, with lower viscosity in Al-rich regions and higher viscosity in Ni-rich regions. To understand the structural origins of these behaviors, we analyzed chemical short-range order and local fivefold symmetry structures using Warren-Cowley parameters and fivefold symmetry parameters, uncovering a close correlation between atomic-scale structural features and dynamic properties. Evaluation of the Stokes-Einstein relation revealed varying degrees of deviation from its predicted viscosity values across composition regions. We observed a negative correlation between free volume fraction and viscosity, with varying strengths in different regions. These findings provide new perspectives for understanding the complex dynamic properties of Ti–Al–Ni liquid alloys.

Thermally stable thin-film composite nanofiltration membranes derived from 3,3′-diaminobenzidine

The rapid development of modern industrialization has put forward high demands on separation and purification technologies. To reduce energy consumption, improve efficiency, and enhance process flexibility, nanofiltration membranes for high temperature separation have become more and more important. Herein, we report the use of 3,3′-diaminobenzidine (DAB) as the aqueous phase monomer and trimesoyl chloride (TMC) as the organic phase monomer to engineer thermally resistant nanofiltration membranes via interfacial polymerization. The incorporation of DAB enhances the rigidity of the cross-linked polyamide network, reduces segmental thermal motion at high temperature, and improves the thermal stability of the composite membrane. The variations in fractional free volumes of the nanofiltration membranes were analyzed at different temperatures by molecular dynamics (MD) simulation, which have also been confirmed by experiments. The findings reveal that incorporating a rigid monomer into the polyamide layer can significantly enhance the thermal resistance. The resultant composite membrane exhibits outstanding resistance to high-temperature feed solutions, boasting a highly stable rejection rate (97.0 %) to Na2SO4 between 25–85 °C. Remarkably, even under sustained operation at 85 °C for 12 h, the rejection rate is consistently stable. This work presents a novel system for the design of thermally stable nanofiltration membranes for high temperature separation.

Dibenzodioxin-Based Polymers of Intrinsic Microporosity with Enhanced Transport Properties for Lithium Ions in Aqueous Media.

Boosting the transport and selectivity properties of membranes based on polymers of intrinsic microporosity (PIMs) toward one specific working analyte of interest is challenging. In this work, a novel family of PIM membranes, prepared by casting and exhibiting optima mechanical properties and high thermal stability, was synthesized from 4,4'-(2,2,2-trifluoro-1-phenylethane-1,1-diyl) bis(benzene-1,2-diol) and two tetrafluoro-nitrile derivatives. Gas permeability measurements evidenced a CO2/CH4 selectivity up to 170% relative to the reference polymer, PIM-1, in agreement with their calculated fractional free volume and the analysis of the textural properties by N2 and CO2 gas adsorption. Besides, the chemical modification by acid hydrolysis of the PIM membranes favored the permeability for lithium ions (LiCl 2M, 6 × 10-9 cm2·s-1) compared to other alkali metal analogs such as sodium (NaCl 2M, 7.38 × 10-10 cm2·s-1) and potassium (KCl 2M, 1.05 × 10-9 cm2·s-1). Moreover, the complete mitigation of the crossover of redox species with higher molecular sizes than the ions from alkali metal salts was confirmed by using in-line benchtop NMR methods. Additionally, the modified PIM membranes were measured in a symmetric electrochemical flow cell using an aqueous electrolyte by combining lithium ferro/ferricyanide redox compounds and lithium chloride. The electrochemical tests showed low polarization, high-rate capability, and capacity retention values of 99% when cycled at 10 mA·cm-2 for over 50 cycles. Based on these results, these polymers could be used as highly selective and conducting membranes in electrodialysis for lithium separation and lithium-based redox flow batteries and as a protective layer in high-energy density lithium metal batteries.

Multiscale revelation of asphalt morphology and adhesion performance evolution during stress relaxation process

The objective of this study is to investigate the evolution of asphalt morphology and adhesion properties during stress relaxation using atomic force microscopy (AFM) and molecular dynamics (MD) simulations. Changes in surface roughness, Derjaguin-Muller-Toporov (DMT) modulus, adhesion force, and force-distance curves were analyzed. Morphological and adhesion property evolution was assessed using correlation length and Lyapunov exponent. MD simulations provided insights into the internal stress-time relationship and free volume fraction of asphalt during relaxation. Results indicate that under constant tensile strain, the “bee structure” on the asphalt surface elongates, dark pits transform into light protrusions, microcracks heal, and surface roughness stabilizes after 10 h. Under compressive strain, similar changes occur but are more pronounced during tensile relaxation. The combined use of AFM and MD simulations offers a comprehensive understanding of the microscopic evolution mechanisms of asphalt under stress relaxation, providing valuable insights for optimizing asphalt pavement design and maintenance.