Fractional Free Volume Research Articles

Largely enhanced damping performance of nitrile rubber/ethylene–vinyl acetate blends via phenolic resin-induced phase separation

The low glass transition temperature (Tg) and narrow effective damping temperature range (EDTR) greatly restrict the application of common vulcanized rubbers in fields relating to high temperature environmental condition due to the greatly reduced damping performances. In this work, phenolic resin (PR) was incorporated into nitrile rubber/ethylene–vinyl acetate (NBR/EVM) blends through melt-compounding processing, and the microstructure and damping performance changes induced by PR were comparatively investigated. The results show that PR induces the phase separation of the blends and most of PR particles selectively locate in the NBR component. Molecular dynamics simulation confirms that more hydrogen bonds form in the ternary blends, and reduced free volume fraction is also achieved. The ternary blends show good high-temperature damping performances, and apparently enhanced Tg (up to 17.7 °C) and EDTR (82.6 °C, from −2.6 to 80 °C) are also achieved. Additionally, the ternary blends exhibit good mechanical properties, including higher ductility and larger fracture energy, and better energy dissipation ability. This work provides an alternative resolution way to enhance the damping performances of the common vulcanized rubbers at high temperatures.

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.

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.

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.

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.

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.

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.

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.

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 300-370 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.

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.

Kinetics of Low Molecular Substances Sorption by the Polymer Mixtures

The sorption capacity of polymer blends was analyzed on the basis of absorption kinetics. The study was carried out in an adsorption-active medium with different degrees of deformation. Heptane and butanol were used as adsorption-active media. The influence of the chemical nature of the adsorbate on the sorption process was studied. The free volume fractions for each sample of the composition were calculated. The ability of materials to absorb different amounts of substances allows us to identify the behavior peculiarities of the interfacial regions of different chemical compositions.

Solvent diffusion mechanism of gun propellant revealed through molecular dynamics simulation

Drying is an important operational unit in the preparation of nitrocellulose-based gun propellant, which affects the drying quality and drying rate of the product. The diffusion properties of solvents during the drying process determine the rate of internal solvent removal from the gun propellant, so the diffusion behaviors of ethanol and acetone in the gun propellant were investigated based on molecular dynamics simulations. Three models of single-, double- and triple-base gun propellant components were established, and the interactions between the solvent and the components of gun propellant were investigated by radial distribution function, hydrogen bonding and interaction energy calculations, and the free volumes, diffusion coefficients and the activation energies of the solvents were used to describe the solvent diffusion performances. The results showed that the interaction between ethanol and the components of the gun propellant was mainly hydrogen bonding, and the interaction between acetone and the components was mainly van der Waals forces. When the mass ratio of ethanol and acetone is 1:1, the interaction energy between ethanol and the components is greater due to the presence of strong hydrogen bonding, which resulted in a higher diffusion activation energy of ethanol. However, since the molecular volume of ethanol is higher than that of acetone, it makes the diffusion coefficient of ethanol larger. Compared with single-base gun propellant, after adding nitroglycerin and nitroguanidine, the free volume fraction decreases, the sum of the interaction energies between the solvent and the components in gun propellant increases, and the diffusion activation energy increases. Hence, this present work regarding the study of solvent diffusion mechanism of gun propellant can provide theoretically guiding suggestion to the actual drying process and manufacture of gun propellant.

Mechanical reinforcement and confinement in elastomeric corn starch/bentonite nanocomposites

The mechanical reinforcement of plasticized corn starch (CS) films induced by bentonite nanoclay was investigated using dynamic mechanical analysis and rheology. Dynamic temperature scans revealed mechanical reinforcement from cryogenic to high temperatures, and two mechanical relaxations named α and α’. The lower temperature relaxation α was associated with long range cooperative molecular motions typical of the glass transition and it was associated to glycerin-rich domains, ranging from −60 °C to −40 °C. The mechanical relaxation α′ was detected in the range −30 °C to −10 °C and it may be associated to phase separated starch-rich domains. The morphology was a function of bentonite concentration, at cbentonite<3 wt% the nanoplatelets were exfoliated and c ≥ 3 wt% they were intercalated. Strikingly, at 3 wt% bentonite content the elastic modulus E′ increased drastically. The viscoelastic properties showed that the geometrical confinement exerted by the nanoplatelets also induced a decrease of fractional free volume fg and of apparent molecular weight between crosslinks Mc,app, and an increase of the activation energy Ea of the α’ relaxation. Spatial confinement in the intercalated morphology appears to be the source of mechanical reinforcement of CS/bentonite nanocomposites.

Long-chain alkyl emulsifiers induced asphalt particle dispersion: Lipophilicity-enhancement effect

The structure of the lipophilic groups within the emulsifiers plays a pivotal role in uniformly dispersing the asphalt particles in the water regarding the storage and thermal stability of emulsified asphalt. This study combines laboratory experiments with molecular dynamics simulations, investigating the influence of alkyl chain length on emulsified asphalt dispersion and behavior at the oil/water interface. The results reveal that long-chain alkyl emulsifiers (C16TAC and C18TAC) present a lipophilicity-enhancement effect. This phenomenon increases the free volume fraction of emulsified asphalt, reducing viscosity and improving the compatibility of emulsion. This results in smaller asphalt particle sizes (D50 = 1.982μm) and more uniform dispersion. Vigorously lipophilic long-chain alkyl promotes emulsifier molecular migration towards the asphalt phase, thickening the oil/water interfacial layer and reducing interfacial tension and energy by more than 90 %. Notely, long-chain alkyl emulsifiers establish strong hydrogen bonds with water molecules, leading to water molecule aggregation into a hydration layer. Laboratory experimental results demonstrate that this lipophilicity-enhancement effect significantly improves the storage and thermal stability of emulsified asphalt. This research recommends long-chain alkyl emulsifiers in developing and designing energy-efficient pavement engineering regarding high-performance emulsified asphalt.

Phase behavior of the carbon dioxide/toluene/poly(ethylene glycol) ternary system

The phase behavior of a carbon dioxide (CO2)/toluene (Tol)/poly(ethylene glycol) (PEG) ternary system was investigated in this study to consider the effect of the polymer species on the phase diagram. Measurements were performed using a synthetic method combined with laser displacement and turbidity measurements. Bubble points (vapor–liquid phase separation) were determined from changes in the piston displacement and cloud points (liquid–liquid (LL) phase separation) were determined from changes in the turbidity. The phase boundaries of the CO2 mass fractions ranging from 0.113 to 0.496 were measured by varying the Tol/PEG mass ratio. The homogeneous phase area decreased when the mass ratio of PEG to Tol increased and/or the temperature decreased. These changes in the LL phase-separation behavior were explained by referring to the free volume fraction and solubility parameter estimated using the Sanchez–Lacombe equation of state. The free volume integral fraction could explain the phase diagram, but not the solubility parameter; the effect of polymer species on the Px phase diagram of the ternary system was explained by considering specific interactions between dissimilar components. These results could promote a comprehensive understanding of the phase diagram of CO2/organic solvent/polymer systems and aid the prediction of phase behavior.

MDI-PTMG-based TPU modified asphalt: Preparation, rheological properties and molecular dynamics simulation

Thermoplastic polyurethane elastomer (TPU) modified asphalt was prepared by a two-step process using MDI and PTMG. The improvement effects of different TPU content on high-and low-temperature rheological properties and thermal stability of asphalt were studied through experimental tests. The results showed that TPU could enhance the high-temperature properties of asphalt obviously. The improvement effect was more significant with the increase of TPU content. At the same time, glass transition temperature (Tg) of asphalt decreased with the increase of TPU content, indicating that TPU could improve the low-temperature performance of asphalt. These experimental results were further verified by the Molecular dynamics (MD) simulation results. Materials Studio 8.0 was used to establish the molecular models of asphalt, TPU and TPU modified asphalt. The effects of TPU content on mechanical modulus and Tg of asphalt were studied by MD simulation. The results revealed that TPU formed a close structure with asphalt to improve the structural stability of asphalt. And the free volume fraction of the modified asphalt decreased with the increase of TPU content. Thus, the high-temperature properties of asphalt were improved. The calculated Tg and moduli obtained from MD simulation accorded well with the experimental results from DSC and DSR, respectively. This study suggests a novel way to provide guidance for the development of TPU modified asphalt.