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This paper aims to investigate the contribution of tool wear and process parameters to the shape defects induced by the micro-machining of glassy polymers such as polycarbonate. An experimental approach is proposed in this study using an instrumented orthogonal cutting configuration. Diamond inserts have been considered as a cutting tool and have been subjected to different levels of accelerated wear. The worn tools were first characterized to identify the wear mechanisms that occurred on the active cutting zone and were then used to perform orthogonal cutting experiments on polycarbonate. Micro-cutting depth values (3–20 µm) were considered to respect the micro-machining configuration. Chip morphology, cutting forces, and machined surfaces' topography have been acquired to analyze and assess the effectively removed material depth regarding the theoretical cutting depth for each worn tool. Results show that the increase of the cutting edge radius is the main wear mechanism that occurred in the diamond inserts. This tool wear evolution was found to be the most influential factor on the induced shape defect by increasing the elastic deformation of polycarbonate rather than its shear when using micro-cutting depths, which induces a spring-back of polycarbonate after cutting. [ABSTRACT FROM AUTHOR]

Cold forming of polycarbonate films results in the formation of shear bands in the necking zone. The numerical results obtained from standard viscoplastic material models exhibit mesh size dependency, requiring mathematical regularization. For this purpose, we present in this work a large deformation gradient theory for a viscoplastic isotropic material model published before. We extend our model to a micromorphic model by introducing a new micromorphic variable as an additional degree of freedom along with its first gradient. This variable represents a microequivalent plastic strain. The relation between the macroequivalent plastic strain and the micromorphic variable is accomplished by a micromorphic coupling modulus. This coupling forces proximity between the macro- and microvariables, leading to the targeted regularization effect. The micromorphic model is implemented as a three-dimensional initial boundary value problem in an in-house finite element tool. The analysis is performed for both uniaxial and biaxial specimens. The provided numerical examples show the ability of our model to regularize shear bands within the specimens and address the issue of localization. [ABSTRACT FROM AUTHOR]

This paper aims to investigate the cutting behavior of optical glassy polymers in order to identify the shape defects induced by the micro-machining processes. Polycarbonate (PC), Allyl Diglycol Carbonate (CR39), and polythiourethane (MR7) polymers are considered in this study to perform micro-machining experiments using the orthogonal cutting configuration. The comparative analysis is carried out by conducting the cutting experiments on hybrid samples that are composed of two types of polymers (MR7-PC, CR39-PC, and MR7-CR39) and then comparing the topographic state of the machined hybrid surfaces. Results show that PC is by far the polymer that generates the most shape defects because of its high rate of spring-back. This finding has been validated by nanoindentation experiments that reveal the highest mechanical reaction of PC at the time of nanoindentation unloading. This study demonstrates also that the measured thrust forces could be an indicator for predicting the spring-back defects induced by micro-machining. [ABSTRACT FROM AUTHOR]

Abstract Hysteretic sorption and desorption of water is observed from 0 to 95% relative humidity and 298–333 K on a glassy polyurethane foam. It is postulated that sorption-induced swelling of the glassy polyurethane increases the concentration of accessible hydrogen-bonding adsorption sites for water. The accessibility of sites is kinetically controlled due to the restricted thermal motions of chains in the glassy polymer, causing a difference in accessible site concentrations during sorption and desorption. This discrepancy leads to hysteresis in the sorbed concentrations of water. A coupled chemo-mechanical model relating volumetric strain, adsorption site concentration, and sorbed water concentration is employed to describe water sorption hysteresis in the glassy polyurethane. This model not only describes the final mass uptake for each relative humidity step, but also captures the dynamics of water uptake, which exhibit diffusion and relaxation rate-controlled regimes.

Hysteretic sorption and desorption of water is observed from 0 to 95% relative humidity and 298–333 K on a glassy polyurethane foam. It is postulated that sorption-induced swelling of the glassy polyurethane increases the concentration of accessible hydrogen-bonding adsorption sites for water. The accessibility of sites is kinetically controlled due to the restricted thermal motions of chains in the glassy polymer, causing a difference in accessible site concentrations during sorption and desorption. This discrepancy leads to hysteresis in the sorbed concentrations of water. A coupled chemo-mechanical model relating volumetric strain, adsorption site concentration, and sorbed water concentration is employed to describe water sorption hysteresis in the glassy polyurethane. This model not only describes the final mass uptake for each relative humidity step, but also captures the dynamics of water uptake, which exhibit diffusion and relaxation rate-controlled regimes. [ABSTRACT FROM AUTHOR]

Aging in polymers of intrinsic microporosity has slowed exploitation due to a decay in performance over time since densification makes them unsuitable for industrial applications. This work aimed to study the impact of the operation and storage temperature on the gas separation properties and aging rates of PIM-1 self-standing films. The permeability, diffusivity, and solubility of the tested membranes were monitored through permeation tests for pure carbon dioxide and nitrogen at a maximum upstream pressure of 1.3 bar for temperatures ranging from −20 °C to 25 °C. This study found significant benefits in the operation of glassy polymeric membranes at low temperatures, resulting in a favourable trade-off in separation performance and a reduction in the aging rate by three orders of magnitude. This brings new opportunities for the industrial application of PIMs in innovative carbon capture processes.

When surface-active molecules or particles assemble at fluid–fluid interfaces, these interfaces acquire complex rheological properties that are of importance in processes that involve flow and deformation of interfaces. Although much progress has been made, interfacial rheology measurements and, in particular, the measurement of interfacial rheological properties of polymers at the air-water interface remain challenging. These are due to weak interactions with the water subphase, the polymer backbone conformation, the glass transition of the interfacial layer, and memory effects. In the present work, we describe systematic rheological measurements of polymer-laden interfaces. The measurements were performed with four different interfacial shear rheometers that can be classified into two types: rheometers in which the surface pressure can be controlled independently, and devices based on fixtures mounted on standard rotational rheometers and lacking control of the surface pressure. We use poly(tert-butyl methacrylate) and poly(methyl methacrylate), two high glass transition temperature, hydrophobic polymers anchored to the water subphase by means of the acrylate group. Using a Langmuir–Pockels (LP) trough, we identify the transition of the polymer monolayer from a viscous to a solid elastic or soft-glassy interface as the polymer surface concentration increases by compression. Then, we compare the linear viscoelastic properties of the interface as obtained by each rheometer. Our results show poor reproducibility and comparability of the rheological data as obtained by different rheometers for the same polymer. This is mainly due to differences in the method used to prepare the layers. For LP-based devices, spreading under dilute conditions and subsequent compression yields layers of compressed glassy blobs with reproducible results. On the other hand, for devices without surface pressure control, deposition of the amount needed to reach a desired concentration may lead to the formation of ill-defined layers resulting in irreproducible data. Furthermore, we find that only when spreading the polymer to form a dilute layer and then controlling the surface pressure by compression, we can clearly distinguish the fluidlike from solidlike interfaces, and a clear correlation is observed between the surface pressure (or interfacial polymer concentration) and the rheological properties of the interface. [ABSTRACT FROM AUTHOR]

When surface-active molecules or particles assemble at fluid–fluid interfaces, these interfaces acquire complex rheological properties that are of importance in processes that involve flow and deformation of interfaces. Although much progress has been made, interfacial rheology measurements and, in particular, the measurement of interfacial rheological properties of polymers at the air-water interface remain challenging. These are due to weak interactions with the water subphase, the polymer backbone conformation, the glass transition of the interfacial layer, and memory effects. In the present work, we describe systematic rheological measurements of polymer-laden interfaces. The measurements were performed with four different interfacial shear rheometers that can be classified into two types: rheometers in which the surface pressure can be controlled independently, and devices based on fixtures mounted on standard rotational rheometers and lacking control of the surface pressure. We use poly(tert-butyl methacrylate) and poly(methyl methacrylate), two high glass transition temperature, hydrophobic polymers anchored to the water subphase by means of the acrylate group. Using a Langmuir–Pockels (LP) trough, we identify the transition of the polymer monolayer from a viscous to a solid elastic or soft-glassy interface as the polymer surface concentration increases by compression. Then, we compare the linear viscoelastic properties of the interface as obtained by each rheometer. Our results show poor reproducibility and comparability of the rheological data as obtained by different rheometers for the same polymer. This is mainly due to differences in the method used to prepare the layers. For LP-based devices, spreading under dilute conditions and subsequent compression yields layers of compressed glassy blobs with reproducible results. On the other hand, for devices without surface pressure control, deposition of the amount needed to reach a desired concentration may lead to the formation of ill-defined layers resulting in irreproducible data. Furthermore, we find that only when spreading the polymer to form a dilute layer and then controlling the surface pressure by compression, we can clearly distinguish the fluidlike from solidlike interfaces, and a clear correlation is observed between the surface pressure (or interfacial polymer concentration) and the rheological properties of the interface. [ABSTRACT FROM AUTHOR]

The properties of films prepared from polystyrene (PS), poly(methyl methacrylate) (PMMA), and polystyrene (PS)/poly(methyl methacrylate) (PMMA) blends and composite films prepared with metal ion-centered complexes were compared. New complexes of Cr(III), Co(II), Ni(II), and Cu(II) prepared according to the template were synthesized from ligand L (4-hydroxy-N-[2-[(4-hydroxybenzoyl)amino]ethyl]benzamide) prepared by condensation of 4-hydroxybenzoic acid and ethylenediamine. Structural analysis of ligands and complexes were determined by LC-MS, 1H-NMR, FTIR, UV-Vis, and XRD. The conductivities and magnetic susceptibility of novel complexes were measured. Morphological properties of the transparent films by SEM and AFM, their thermal stabilities by TGA, and their optical properties by refractometry were characterized. Original composite films of PS, PMMA, and PS/PMMA blend modified with novel complexes were obtained as thermally stable, transparent, and foldable composite films with permanent colors. [ABSTRACT FROM AUTHOR]

Sorption of pure CO2 and CH4 and CO2/CH4 binary gas mixtures in amorphous glassy Poly(2,6-dimethyl-1,4-phenylene) oxide (PPO) at 35 °C up to 1000 Torr was investigated. Sorption experiments were carried out using an approach that combines barometry with FTIR spectroscopy in the transmission mode to quantify the sorption of pure and mixed gases in polymers. The pressure range was chosen to prevent any variation of the glassy polymer density. The solubility within the polymer of the CO2 present in the gaseous binary mixtures was practically coincident with the solubility of pure gaseous CO2, up to a total pressure of the gaseous mixtures equal to 1000 Torr and for CO2 mole fractions of ~0.5 mol mol−1 and ~0.3 mol mol−1. The Non-Equilibrium Thermodynamics for Glassy Polymers (NET-GP) modelling approach has been applied to the Non-Random Hydrogen Bonding (NRHB) lattice fluid model to fit the solubility data of pure gases. We have assumed here that no specific interactions were occurring between the matrix and the absorbed gas. The same thermodynamic approach has been then used to predict the solubility of CO2/CH4 mixed gases in PPO, resulting in a deviation lower than 9.5% from the experimental results for CO2 solubility. [ABSTRACT FROM AUTHOR]

Polymer matrices, when placed in contact with a fluid phase made of low molecular weight compounds, undergo a depression of their glass transition temperature (Tg) determined by the absorption of these compounds and the associated plasticization phenomena. Frequently, this effect is coupled with the mechanical action of the compressive stress exerted by the pressure of the fluid phase that, in contrast, promotes an increase in the Tg. This issue is relevant for technological and structural applications of composites with high-performance glassy polymer matrices, due to their significant impact on mechanical properties. We propose an approach to model and predict rubbery-glassy states maps of polymer–penetrant mixtures as a function of pressure and temperature based on the Gibbs–Di Marzio criterion. This criterion establishes that a 'thermodynamic' glass transition does occur when the configurational entropy of the system vanishes. Although questioned and criticized, this criterion constitutes a good practical approach to analyse changes of Tg and, in some way, reflects the idea of an 'entropy catastrophe' occurring at the glass transition. Several polymer–penetrant systems have been analysed modelling configurational entropy by means of the Non-Random Hydrogen Bond lattice fluid theory, able to cope with possible non-random mixing and occurrence of strong interactions. This article is part of the theme issue 'Ageing and durability of composite materials'. [ABSTRACT FROM AUTHOR]

We identify for visco-elasto-plastic (VEP) glassy polymers, physical phenomena during Berkovich nanoindentation, a locally imposed deformation. Live visuals via in situ nanoindentation indicate mainly sink-in during loading, with pile-up after unloading. Scanning Probe Microscopy (SPM) indicates significant volume conserving upflow below the tip, for these high ν , compliant materials, with compliance correlated high geometric fractional contact, h c Δ h m Δ ∼ 0.86 − 0.95. We adapt the ideal conical indentation framework to VEP Berkovich nanoindentation, to calculate the contact area and visually depict the upflow and the displacement paths, in the material. The combination of SPM and P − h data, indicates a mixed comparison with uniaxial modulus and yield stress, with conventionally defined hardness, H < 3 σ y , and nanoindentation modulus, E N > E. By rationally removing viscoelastic (VE) effects from the loading P − h data, we find instant, zero-time hardness H L 0 > 3 σ y. We apply the power law model to only the recovery onset, to estimate pure elastic recovery. We then deconvolute the VEP nanoindentation into the conventional EP (elasto-plastic) and elastic contributions, isolating the VE component. Constraint-induced sink-in, pile-up and VE recovery of the highly yielded tip-apex region, mirror the converse constrained deformation effects, governing the trends in the conventional EP E N and H L 0 estimates for glassy polymers. [Display omitted] • Sink-in and pile-up coexist and high contact fraction help bottom-up phenomena view. • Estimate full-load topology for viscoelastoplastic Berkovich nanoindentation. • Compression to lateral Poisson expansion to vertical Poisson (least resistance path). • Dichotomy in modulus and hardness help deconvolute viscoelastoplastic deformation. • Constraint forced extra recovery of apex mirrors constrained deformation effects. [ABSTRACT FROM AUTHOR]

[Display omitted] • The simulated glassy polymer films are confirmed to be process dependent. • The PVD-inspired computational procedure is proposed for glassy polymer film. • An optimal temperature of middle layer is identified for greatest film stability. • Free surfaces of glassy polymer films are responsible for the enhanced stability. A molecular dynamics (MD) framework has been proposed to systematically simulate process (but not cooling rate) dependent properties of glassy polymer films. With the coarse-grained (CG) polylactide (PLA) of low molecular weight (MW), the simulated thermal properties of glassy films are confirmed to be surely decided by the routes to prepare them. While the glassy films initially prepared from the melt bulk are stable, the glassy film initially constructed from the glassy bulk appears to be unstable, featuring highest potential energy among those films and different averaged heat capacity from the bulk counterparts. Inspired by physical vapour deposition (PVD), a surface formation process is further applied to the unstable film to generate stable glassy polymer films. Similar to the PVD, an optimal temperature at which the film is most stable can be identified with lower potential energy than the conventional films, for which free surface and enhanced order of the middle layer are responsible. This work paves a way for obtaining simulated models of stable glassy films and experimentally preparing advanced glassy films for high MW polymers, which otherwise are hard to be realized by the PVD process. [ABSTRACT FROM AUTHOR]

In this paper, we use molecular dynamics (MD) simulations to investigate the origin of strain hardening in glassy polymers, with a particular focus on the influences of strain rate and temperature. We demonstrate that strain hardening in uniaxial tension arises from bond stretching and is relaxed by bond rotation, characterized by the evolution of dihedral angles. Based on this rotational relaxation, strain rate plays a role analogous to temperature, resulting in a steady state behavior in the hardening region identifiable by strain rate and temperature. Following these observations, we propose a constitutive model to describe the rate- and temperature-dependent strain hardening behavior of glassy polymers using a viscous potential as a function of strain rate. To capture the elastic and yield behavior at small strains, we integrate this viscous potential with a conventional elasto-viscoplastic (EVP) model, giving rise to our V-EVP model. The V-EVP model is shown to be thermodynamically consistent and is validated by comparison to MD simulation results of glassy polymers undergoing uniaxial tension tests across a broad range of temperatures and strain rates. • We addressed the physical origin of rate- and temperature-dependent strain hardening, • observed steady-state stress response in the hardening region, • proposed a new constitutive model framework for the steady-state hardening behavior. [ABSTRACT FROM AUTHOR]

The temperature dependence of low-frequency IR spectra of glassy polymers in the range ν = 0.24–4 THz (8–135 cm−1) at temperatures from 90 to 400 K has been studied. Their analysis made it possible to detect absorptions corresponding to both individual and correlated torsional vibrations, which couple to the manifestation of relaxation dynamics. The temperature evolution of IR spectra at terahertz frequencies shows 3 universal features: low-temperature, corresponding to the anharmonicity of torsional-vibrational motion, high-temperature, due to the contribution of the α-relaxation (glass transition), and intermediate, associated with unfreezing of the conformational mobility of chains during the β-transition. The results obtained were shown to be applicable to polymers with both hydrogen and van der Waals bonds between the macromolecules. [ABSTRACT FROM AUTHOR]

The first commercial hollow fiber and flat sheet gas separation membranes were produced in the late 1970s from the glassy polymers polysulfone and poly(vinyltrimethyl silane), respectively, and the first industrial application was hydrogen recovery from ammonia purge gas in the ammonia synthesis loop. Membranes based on glassy polymers (polysulfone, cellulose acetate, polyimides, substituted polycarbonate, and poly(phenylene oxide)) are currently used in various industrial processes, such as hydrogen purification, nitrogen production, and natural gas treatment. However, the glassy polymers are in a non-equilibrium state; therefore, these polymers undergo a process of physical aging, which is accompanied by the spontaneous reduction of free volume and gas permeability over time. The high free volume glassy polymers, such as poly(1-trimethylgermyl-1-propyne), polymers of intrinsic microporosity PIMs, and fluoropolymers Teflon® AF and Hyflon® AD, undergo significant physical aging. Herein, we outline the latest progress in the field of increasing durability and mitigating the physical aging of glassy polymer membrane materials and thin-film composite membranes for gas separation. Special attention is paid to such approaches as the addition of porous nanoparticles (via mixed matrix membranes), polymer crosslinking, and a combination of crosslinking and addition of nanoparticles.

Sorption of pure CO2 and CH4 and CO2/CH4 binary gas mixtures in amorphous glassy Poly(2,6-dimethyl-1,4-phenylene) oxide (PPO) at 35 °C up to 1000 Torr was investigated. Sorption experiments were carried out using an approach that combines barometry with FTIR spectroscopy in the transmission mode to quantify the sorption of pure and mixed gases in polymers. The pressure range was chosen to prevent any variation of the glassy polymer density. The solubility within the polymer of the CO2 present in the gaseous binary mixtures was practically coincident with the solubility of pure gaseous CO2, up to a total pressure of the gaseous mixtures equal to 1000 Torr and for CO2 mole fractions of ~0.5 mol mol−1 and ~0.3 mol mol−1. The Non-Equilibrium Thermodynamics for Glassy Polymers (NET-GP) modelling approach has been applied to the Non-Random Hydrogen Bonding (NRHB) lattice fluid model to fit the solubility data of pure gases. We have assumed here that no specific interactions were occurring between the matrix and the absorbed gas. The same thermodynamic approach has been then used to predict the solubility of CO2/CH4 mixed gases in PPO, resulting in a deviation lower than 9.5% from the experimental results for CO2 solubility.

The effects of annealing a glassy polymer at temperatures well below Tg on the dynamic linear viscoelastic properties were investigated. The polymer was an epoxy thermoset with a Tg of 182°C. Specimens were annealed from 2 h to up to 600 h at temperatures from −100°C (Tg −282°C) up to Tg. At annealing temperatures just below Tg, there was no effect of annealing, and annealing at −100°C (Tg −282°C) showed no difference between 2 and 6 h annealing, although annealing effects might be seen at longer times. At temperatures between −50°C (Tg −232°C) and 170°C (Tg −12°C) the storage isotherms increased with annealing while the loss isotherms decreased. In addition, the heat capacity as measured via DSC after annealing at 50°C (Tg −132°C) and 100°C (Tg −82°C) exhibited endothermic peaks approximately 40°C above the annealing temperature. This study clearly shows that a material deep in the glassy state is not frozen, but undergoes continuing evolution. The nature of deep glass aging is different than physical aging in the Tg region, where deep in the glass the relaxation spectrum changes magnitude and shape but does not shift along the log frequency axis in contrast to physical aging in the Tg region. [ABSTRACT FROM AUTHOR]

Scintillating materials emit light when exposed to ionizing radiation or particles and are used for the detection of nuclear threats, medical imaging, high-energy physics, and other usages. For some of these applications, it is vital to distinguish neutrons and charged particles from γ-rays. This is achievable by pulse shape discrimination (PSD), a time-gated technique, which exploits that the scintillation kinetics can depend on the nature of the incident radiation. However, it proves difficult to realize efficient PSD with plastic scintillators, which have several advantages over liquid or crystalline scintillating materials, including mechanical robustness and shapeability. It is shown here that sensitive and rapid PSD is possible with nanostructured polymer scintillators that consist of a solid polymer matrix and liquid nanodomains in which an organic dye capable of triplet-triplet annihilation (TTA) is dissolved. The liquid nature of the nanodomains renders TTA highly efficient so that delayed fluorescence can occur at low energy density. The nanostructured polymer scintillators allow discriminating α particles, neutrons, and γ-rays with a time response that is better than that of commercial scintillators. Exploiting that the liquid nanodomains can facilitate energy transfer processes otherwise difficult to realize in solid polymers, an auxiliary triplet sensitizer is incorporated. This approach further increases the scintillator's sensitivity toward α particles and neutrons and other high-energy processes where localized interactions are involved., (© 2024 Wiley‐VCH GmbH.)

Aging in polymers of intrinsic microporosity has slowed exploitation due to a decay in performance over time since densification makes them unsuitable for industrial applications. This work aimed to study the impact of the operation and storage temperature on the gas separation properties and aging rates of PIM-1 self-standing films. The permeability, diffusivity, and solubility of the tested membranes were monitored through permeation tests for pure carbon dioxide and nitrogen at a maximum upstream pressure of 1.3 bar for temperatures ranging from -20 °C to 25 °C. This study found significant benefits in the operation of glassy polymeric membranes at low temperatures, resulting in a favourable trade-off in separation performance and a reduction in the aging rate by three orders of magnitude. This brings new opportunities for the industrial application of PIMs in innovative carbon capture processes.

The alignment of polymer chains within polycarbonate (PC) significantly influences the mechanical properties of the deformed specimen. This influence can be affected by both the global stretch rate and the type of loading. The objectives of the current work are to investigate uniaxial film, bar specimens, and biaxial thick-walled specimens using 3D-optical measurements. Our approach involves developing different methods to determine the local inhomogeneous strain fields for both thin and thick-walled uniaxial specimens. In the pure tension case and under the assumption of uniaxial plane stress, we utilize the strains to calculate the local volume ratio and, consequently, approximate the local true stress at different axial positions of the specimen. Additionally, we investigate the effect of variations in global stretch rates on local stresses. Furthermore, we explore induced anisotropy for different global stretching ratios. Another objective is to investigate biaxial specimens under sequential and simultaneous biaxial stretching conditions, examining the impact of both stretching types on the mechanical and structural properties of the material. [Display omitted] • Mechanical properties of polycarbonate are strongly influenced by polymer chains alignment. • Developing methods for evaluating local strain within uniaxial specimens. • Local and global approximated stresses are rate-dependent. • Sequential biaxial stretching leads to unbalanced mechanical properties. • Equibiaxial biaxial stretching leads to equal mechanical properties in all directions. [ABSTRACT FROM AUTHOR]

FFT-based solvers are increasingly used by many researcher groups interested in modelling the mechanical behavior associated to a heterogeneous microstructure. A development is reported here that concerns the viscoelastic behavior of composite structures generally studied experimentally through Dynamic Mechanical Analysis (DMA). A parallelized computation code developed with complex-valued quantities provides virtual DMA experiments directly in the frequency domain on a heterogeneous system described by a voxel grid of mechanical properties. The achieved precision and computation times are very good. An effort has been made to illustrate the application of such a virtual DMA tool through two examples from the literature: the modelling of glassy/amorphous systems at a small scale and the modelling of experimental data obtained in temperature sweeping mode by DMA on a particulate composite made of glass beads and a polystyrene matrix, at a larger scale. Both examples show how virtual DMA can contribute to question, analyze, and understand relaxation phenomena on either theoretical or experimental points of view.

In this article, a novel constitutive model using fractional calculus is developed to capture the stress relaxation behavior of glassy polymers, where a variable‐order differential operator based on Marchaud fractional derivative is adopted. To assess the validity of the proposed model, a series of stress relaxation tests of the representative glassy polymer, poly(ethylene glycol‐co‐1,4‐cyclohexanedimethanol terephthalate), are conducted, and the stress responses of the specimens under different ambient temperatures are obtained. In view of the basic theory of fractional viscoelasticity, the varying order is assumed to bea function of time. Through the comparison of the fitting effect and reasonability of four kinds of order function based on the experimental data, it is concluded that the linear order function of time is suitable for our model which shows high accuracy. Moreover, the physical significance of order function is analytically derived, and the rising order is found to have a direct connection with the continuous softening of polymers during relaxation. Deeper investigations manifest that high ambient temperature accelerates the material softening, and the change of microstructures inside polymers could be reflected by the varying order, which is possible to provide a new perspective on manufacturing proper polymers with excellent resistance to stress relaxation. [ABSTRACT FROM AUTHOR]

In this paper, a viscoelastic model able to capture important mechanical features of a wide class of glassy polymers is presented. Among them, the ability of reproducing the highly nonlinear rate-dependent stress response and the post-yield strain softening phenomenon. The simplicity of the proposition allows to recover the same mathematical structure of classical constitutive approaches, well suited for the use of implicit finite element codes. To this aim, the flow resistance concept, elsewhere known as shear strength, is reframed as a state variable of an accumulated strain measure. Three alternative expressions for this function are presented. The model is cast within a variational framework in which consistent constitutive updates are obtained by a minimization procedure. Convenient choices for the conservative and dissipative potentials reduce the local constitutive problem to the solution of a single nonlinear scalar equation, emulating the simplest case of viscoelastic models. Numerical tests on the constitutive model show excellent agreement with experimental data. Finally, a 3D simulation of a standard specimen with heterogeneous material properties illustrates the ability of the present proposition to be implemented in implicit finite element codes. [ABSTRACT FROM AUTHOR]

Glassy polymers are extremely difficult to self-heal below their glass transition temperature (Tg) due to the frozen molecules. Here, we fabricate a series of randomly hyperbranched polymers (RHP) with high density of multiple hydrogen bonds, which show Tg up to 49 °C and storage modulus up to 2.7 GPa. We reveal that the hyperbranched structure not only allows the external branch units and terminals of the molecules to have a high degree of mobility in the glassy state, but also leads to the coexistence of "free" and associated complementary moieties of hydrogen bonds. The free complementary moieties can exchange with the associated hydrogen bonds, enabling network reconfiguration in the glassy polymer. As a result, the RHP shows amazing instantaneous self-healing with recovered tensile strength up to 5.5 MPa within 1 min, and the self-healing efficiency increases with contacting time at room temperature without the intervention of external stimuli. [ABSTRACT FROM AUTHOR]

Investigation of mixed-gas sorption is necessary for robust design and optimization of membrane-based processes. While sorption models for glassy polymers are well-established, they often deviate from observed mixture data. In doing so, however, parameters of these models are typically estimated via traditional least-squares optimization methods, and so parametric uncertainty is often ignored in mixture sorption predictions. As an alternative, we use Bayesian Inference (BI) to estimate probability distributions for sorption models' parameters and thus provide statistically meaningful mixture sorption forecasts that reflect parameter uncertainty rigorously. To this end, we exploit molecular sorption simulations, combining Grand Canonical Monte Carlo (GCMC) and Equilibrium Molecular Dynamics (EMD), to focus on two different glassy polymer systems (i.e., single- and mixed-gas sorption of CO 2 / CH 4 in a fluorinated polyimide and CH 4 / H 2 in a polymer of intrinsic microporosity) and three popular mixture sorption models (the Dual-Mode Sorption model, Non-Equilibrium Thermodynamics for Glassy Polymers model, and the Ideal Adsorbed Solution Theory) to demonstrate the benefits of this technique for uncertainty quantification and propagation in membrane applications. We show that observed sorption data at typical working pressures (e.g., 0 − 25 atm) are often insufficient to accurately estimate model parameters, and consequently, these models often fail to represent observed mixture data adequately. Furthermore, we show that sorption data (e.g., high-pressure data), able to capture intrinsic isotherm nonlinearities of sorption models, are critical to considerably improve parameter inference from collective model-data fits and thus accurately predict mixture sorption. [Display omitted] • Bayesian model-data fitting methods rigorously estimate parametric uncertainty in sorption models. • Numerous sets of parameters accurately fit single-gas sorption data at typical pressures. • Mixed-gas sorption predictions are strongly sensitive to parameter uncertainty. • Single-gas sorption simulations beyond typical pressures significantly decrease parametric uncertainty in sorption models. [ABSTRACT FROM AUTHOR]

The molecular dynamics of poly(1-trimethylsilyl-1-propyne) in the presence of N 2 , CO 2 , CH 4 and C 2 H 4 , is assessed in situ with broadband dielectric and solid state NMR spectroscopies. The measurements of the dielectric permittivity and the analysis of the dielectric spectra show two secondary β relaxations and the absence of a glass transition. These relaxations could be associated to highly flexible and disordered regions (β 1), and to more rigid and ordered ones (β 2). The E a of β 1 observed in the presence of CO 2 was the highest among the four gases studied, suggesting an increased presence in disordered regions. The results of 13C T 1 NMR relaxation measurements provide complementary information on the polymer backbone dynamics. The T 1 s of main chain carbons increase as the concentration of gas sorbed in the polymer increases, indicative of a decrease in chain mobility. The combination of both spectroscopies afforded additional insight toward the understanding of gas transport in glassy microporous polymers. [Display omitted] • PTMSP is a glassy microporous polymer with high free volume fraction and permeability to gases. • BDS and solid state NMR provide information in situ on the molecular dynamics in PTMSP-gas systems. • Carbon dioxide tends to occupied free volume in dense regions of PTMSP membranes. • Increasing concentration of sorbed gas leads to decreasing mobility of polymer chains. [ABSTRACT FROM AUTHOR]

The sorption of CO 2 , CH 4 and CO 2 /CH 4 mixtures in poly(trimethylsilyl propyne) (PTMSP) and PIM-1 (the first reported polymer of intrinsic microporosity) measured in previous works revealed that, in the multicomponent case, significant exclusion effects cause a decrease in solubility with respect to the pure-gas case, and this effect is more pronounced for the less soluble gas (CH 4). In this work we perform a similar experimental analysis on the tetrazole-modified PIM-1 (TZ-PIM), at three mixture compositions (10, 30, 50 mol.% CO 2) and three temperatures (25, 35, 50 °C), up to 35 bar. The obtained trends for solubility and solubility-selectivity of CO 2 , CH 4 , and their mixtures in TZ-PIM are found to be qualitatively and quantitatively comparable to those obtained for other high free volume polymers. Moreover, mixed-gas sorption data collected so far for three materials (TZ-PIM, PIM-1 and PTMSP) are modelled by means of the Non-Equilibrium Lattice Fluid (NELF) model and compared with experimental results. The model was found capable of representing the competitive effects in solubility and solubility-selectivity, in a wide range of temperature and pressure, with a better quantitative accuracy attained at higher temperatures. Finally, by coupling these results with mixed-gas permeation data, an estimate of the mixed-gas diffusivity was obtained, and it was revealed that, in multicomponent conditions, sorption provides a greater contribution to the selectivity than diffusivity, in agreement with experimental findings for similar materials. Image 1 • Mixed-gas CO 2 /CH 4 sorption in TZ-PIM displays strong competitive effects. • Competition enhances the solubility-selectivity in multicomponent conditions. • NELF model yields good predictions of mixed-gas sorption using only pure-gas data as input. • Diffusivity-selectivity in the multicomponent case estimated with the solution-diffusion model. • Solubility-selectivity is higher than diffusivity-selectivity in the mixed-gas case. [ABSTRACT FROM AUTHOR]

The diffusion of small molecules through amorphous polymers proceeds by the thermally activated jumps whose rate changes from one region to another due to polymer heterogeneity. Little is known at present about the origin of diffusion heterogeneity. The oxidation of triplet nitrene and quenching of phenanthrene phosphorescence have been used to study the movement of molecular oxygen on a nanometer length scale in glassy poly(ethyl methacrylate) and poly(n‐butyl methacrylate) far below the glass transition temperature. It has been found that, as temperature increases, the jump rates in all regions increase by the same factor. This finding points to the equality of the activation energies of oxygen jumps in different regions of the polymers. We conclude that the correlated elastic displacements of polymer chains inside regions about several nanometers in size provide molecules jumps. Due to the large size of these regions, the activation energy of jump does not depend on local polymer structure. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1097–1104 [ABSTRACT FROM AUTHOR]

In this study, the rate‐ and temperature‐dependent strain hardening and the Bauschinger effect is studied for three glassy polymers. It appeared that for all materials, an equal distribution of elastic and viscous hardening was necessary to accurately predict the Bauschinger effect, as well as the rate‐ and temperature‐dependent strain hardening response. As for the elastic contribution, the viscous contribution appears to increase with an increase in entanglement network density. Investigating the effect of temperature on the Bauschinger effect revealed that at elevated temperatures the model predictions are not accurately enough. It is shown that this is caused by the magnitude of the elastic hardening contribution; to improve the predictions, a temperature‐dependent elastic contribution is necessary. © 2019 The Authors. Journal of Polymer Science Part B: Polymer Physics published by Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1001–1013 [ABSTRACT FROM AUTHOR]

Abstract The effect of CO 2 on the mechanical properties of three different glassy polymeric materials, polystyrene (PS), polymethylmethacrylate (PMMA) and Matrimid polyimide (PI), has been investigated by dedicated Dynamic Mechanical Analysis (DMA) at 35 °C on samples equilibrated at different penetrant pressures (0–30 bar). The experimental campaign has been designed to inspect the mechanical properties associated to the so-called plasticization phenomenon, which has been invoked as responsible for the increase of gas permeability versus feed pressure in glassy polymeric membranes. The main aim of the work is to find if any correlation holds between the effects induced on polymer mechanical properties and on gas permeability by the presence of different amounts of penetrant gas. The DMA analysis revealed that CO 2 produces a decrease of polymer storage modulus E′ and an enhancement of tan δ factor. Experimental data for both E' and tan δ vary regularly and monotonically with CO 2 content in the membrane, with no indication of the onset of other new phenomena at pressures higher than the "plasticization pressure" associated to permeability data. The mechanical properties show very similar behaviors with CO 2 content for all polymers analyzed, notwithstanding their CO 2 permeability behaviors are different: decreasing with upstream pressure for PS, increasing for PMMA and nonmonotonous for Matrimid. The results obtained indicate that there is no direct correlation between gas permeation dependence on CO 2 content and the changes in the polymer mechanical properties induced by the same CO 2 content. Graphical abstract Image 10685098 Highlights • The mechanical behavior of glassy polymers saturated by CO 2 is investigated by DMA. • Different CO 2 pressures are considered in the range 0–30 bar at 35 °C. • The presence of CO 2 lowers the storage modulus and increases the tan δ coefficient. • No correlation is found between mechanical properties and CO 2 permeability behavior. [ABSTRACT FROM AUTHOR]

Highlights • Experiments on cutting of polymers, with brittle and soft hyperelastic behavior. • Steady state cutting of a sharp thin blade into a thin plate. • Insertion force vs penetration displacement and full-field strain maps are recorded. • Blade sharpness depends on blade profile and material toughness and deformability. • Cut propagation in soft polymers when its tip is reached by the blade. Graphical abstract Abstract An experimental campaign has been carried out with the aim of providing an insight into the fracture processes occurring during the cutting of different types of polymers, with features ranging from typically brittle to soft hyperelastic behaviour. The steady state of cutting is investigated using a sharp thin blade, and tracking the insertion force versus the penetration displacement. For soft, highly-deformable polymers, the influence of large deformations at the crack tip is also taken into account, through full-field finite strain maps obtained by means of digital image correlation. In brittle polymers, the influence of the cutting tool sharpness is discussed with respect to the onset of crack propagation, through a comparison with a simplified analytical model, and numerical finite element analyses. The results suggest that the propagation of the cut clearly depends on the tool sharpness, and for a class of brittle polymers it appears that this may happen as a stable fracture process, with the distance between the blade and the crack tip remaining constant during propagation. On the contrary, soft polymers appear to be much less sensible to the tool profile, and it is the large deformation that ultimately determines the fracture behaviour when the crack tip is reached by the blade. [ABSTRACT FROM AUTHOR]

Global warming by greenhouse gas emissions is one of the main threats of our modern society, and efficient CO2 capture processes are needed to solve this problem. Membrane separation processes have been identified among the most promising technologies for CO2 capture, and these require the development of highly efficient membrane materials which, in turn, requires detailed understanding of their operation mechanism. In the last decades, molecular modeling studies have become an extremely powerful tool to understand and anticipate the gas transport properties of polymeric membranes. This work presents a study on the correlation of the structural features of different membrane materials, analyzed by means of molecular dynamics simulation, and their gas diffusivity/selectivity. We propose a simplified method to determine the void size distribution via an automatic image recognition tool, along with a consolidated Connolly probe sensing of space, without the need of demanding computational procedures. Based on a picture of the void shape and width, automatic image recognition tests the dimensions of the void elements, reducing them to ellipses. Comparison of the minor axis of the obtained ellipses with the diameters of the gases yields a qualitative estimation of non-accessible paths in the geometrical arrangement of polymeric chains. A second tool, the Connolly probe sensing of space, gives more details on the complexity of voids. The combination of the two proposed tools can be used for a qualitative and rapid screening of material models and for an estimation of the trend in their diffusivity selectivity. The main differences in the structural features of three different classes of polymers are investigated in this work (glassy polymers, superglassy perfluoropolymers and high free volume polymers of intrinsic microporosity), and the results show how the proposed computationally less demanding analysis can be linked with their selectivities.

Antiplasticization of glassy polymers, arising from the addition of small amounts of plasticizer, was examined to highlight the developments that have taken place over the last few decades, aiming to fill gaps of knowledge in the large number of disjointed publications. The analysis includes the role of polymer/plasticizer molecular interactions and the conditions leading to the cross-over from antiplasticization to plasticization. This was based on molecular dynamics considerations of thermal transitions and related relaxation spectra, alongside the deviation of free volumes from the additivity rule. Useful insights were gained from an analysis of data on molecular glasses, including the implications of the glass fragility concept. The effects of molecular packing resulting from antiplasticization are also discussed in the context of physical ageing. These include considerations on the effects on mechanical properties and diffusion-controlled behaviour. Some peculiar features of antiplasticization regarding changes in Tg were probed and the effects of water were examined, both as a single component and in combination with other plasticizers to illustrate the role of intermolecular forces. The analysis has also brought to light the shortcomings of existing theories for disregarding the dual cross-over from antiplasticization to plasticization with respect to modulus variation with temperature and for not addressing failure related properties, such as yielding, crazing and fracture toughness.

The transport of gases in glassy polymeric membranes has been analyzed by means of a fundamental approach based on the nonequilibrium thermodynamic model for glassy polymers (NET-GP) that considers the penetrant chemical potential gradient as the actual driving force of the diffusional process. The diffusivity of a penetrant is thus described as the product of a purely kinetic quantity, the penetrant mobility, and a thermodynamic factor, accounting for the chemical potential dependence on its concentration in the polymer. The NET-GP approach, and the nonequilibrium lattice fluid (NELF) model in particular, describes the thermodynamic behavior of penetrant/polymer mixtures in the glassy state, at each pressure or composition. Moreover, the mobility is considered to follow a simple exponential dependence on penetrant concentration, as typically observed experimentally, using only two adjustable parameters, the infinite dilution penetrant mobility L10 and the plasticization factor b, both determined from the analysis of the dependence of steady state permeability on upstream pressure. The available literature data of diffusional time lag as a function of penetrant upstream pressure has been reviewed and compared with model predictions, obtained after the values of the two model parameters (L10 and b), have been conveniently determined from steady state permeability data. The model is shown to be able to describe very accurately the experimental time lag behaviors for all penetrant/polymer pairs inspected, including those presenting an increasing permeability with increasing upstream pressure. The model is thus more appropriate than the one based on Dual Mode Sorption, which usually provides an unsatisfactory description of time lag and required an ad hoc modification. [ABSTRACT FROM AUTHOR]

ABSTRACT Although gas sorption in glassy polymers is a well-studied phenomenon, no general microscopical model is developed which is able to describe the gas sorption in a wide temperature range using only characteristics of polymer and gas molecule. In this work, sorption isotherms and desorption kinetics of O2, Ar, and N2 for glassy poly(ethyl methacrylate) have been measured in the temperature range from 160 to 308 K. To describe both the phenomena, the model is developed which postulates that, in the frozen structure of glassy polymer, any cavities between macromolecules are the sorption sites for small molecules. The cavities of small size can expand elastically to accommodate a gas molecule. The sorption sites are considered to be the potential wells and their depths are distributed according to Gaussian law. The concentration of sorption sites, their mean depth and depths dispersion, and the frequency of molecules oscillations in the sorption sites are the only parameters which determine both the gas transport and sorption. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 288-296 [ABSTRACT FROM AUTHOR]

The transport of gaseous mixtures in glassy polymers is analyzed by means of a thermodynamic based model, which is applied to describe the permeability of CO 2 /CH 4 50/50 binary mixtures in various glassy polymeric membranes. The approach relies on the description of the solubility behavior of penetrant/polymer mixtures provided by the nonequilibrium thermodynamics for glassy polymers (NET-GP), and considers the gradient in penetrant chemical potential of each species as the actual driving force of the diffusive mass fluxes. Such an approach is specialized to dilute solutions conditions, as it is typically of interest for the transport of light gas (e.g. CO 2 , N 2 , CH 4 , O 2 ) in glassy polymeric membranes; that allows for the simple and successful prediction of the gas permeability of gas mixtures based on single component transport data, with no additional parameters required. The NET-GP model is used in combination with an equation of state (lattice fluid theory by Sanchez and Lacombe) to obtain the solubility of pure and mixed gases at various pressures and compositions, as well as the thermodynamic factors accounting for the dependence of chemical potentials of the solutes on the concentrations of both penetrants. An exponential dependence on penetrant concentration is used to describe the mobility coefficient behavior, so that only two adjustable parameters are required for the pure penetrant case (infinite dilution mobility and plasticization factor). A simple but effective linear mixing rule is considered to describe transport in the binary mixture case, which does not introduce any additional adjustable parameter due to the presence of a second penetrating species. The comparison with permeation data of gas mixtures in different polymers shows the good predictive ability of the model. [ABSTRACT FROM AUTHOR]

A set of complementary experiments are used for the first time to elucidate the interrelation between the mechanical properties, the strain field, and the free volume evolution during non-homogenous compression of a glassy polymer. Two sets of quenched and annealed polystyrene samples, having different free volume histories, are notched and exposed to compression. The variation of both the strain field and the free volume are measured on a microscopic scale via digital image correlation in case of strain and Doppler broadening spectroscopy of positron annihilation line in case of free volume measurements. Eventually, the interplay between the local evolution of free-volume, the local strain field, and the mechanical response is investigated throughout the yielding, softening and plateau regions. We found that in all stages of plastic deformation the generated local strain field is positively correlated to the global strain independent of the active mechanism of plastic deformation. Moreover, the local change of free volume is not correlated to the mechanical response of the polymer at the softening stage. Therefore, the free volume evolution should not be responsible for the intrinsic post-yield softening behavior. The easy flow in the plateau region, however, begins at a particular fraction of free volume independent to the thermal history of samples. [ABSTRACT FROM AUTHOR]

A triptycene-based diamine, 1,3,6,8-tetramethyl-2,7-diamino-triptycene (TMDAT), was used for the synthesis of a novel solution-processable polyamide obtained via polycondensation reaction with 4,4′-(hexafluoroisopropylidene)bis(benzoic acid) (6FBBA). Molecular simulations confirmed that the tetrasubstitution with ortho-methyl groups in the triptycene building block reduced rotations around the C⁻N bond of the amide group leading to enhanced fractional free volume. Based on N2 sorption at 77 K, 6FBBA-TMDAT revealed microporosity with a Brunauer⁻Emmett⁻Teller (BET) surface area of 396 m2 g−1; to date, this is the highest value reported for a linear polyamide. The aged 6FBBA-TMDAT sample showed moderate pure-gas permeabilities (e.g., 198 barrer for H2, ~109 for CO2, and ~25 for O2) and permselectivities (e.g., αH2/CH4 of ~50) that position this polyamide close to the 2008 H2/CH4 and H2/N2 upper bounds. CO2⁻CH4 mixed-gas permeability experiments at 35 °C demonstrated poor plasticization resistance; mixed-gas permselectivity negatively deviated from the pure-gas values likely, due to the enhancement of CH4 diffusion induced by mixing effects.

In this paper, the sorption thermodynamics of low-molecular-weight penetrants in a glassy polyetherimide, endowed with specific interactions, is addressed by combining an experimental approach based on vibrational spectroscopy with thermodynamics modeling. This modeling approach is based on the extension of equilibrium theories to the out-of-equilibrium glassy state. Specific interactions are accounted for in the framework of a compressible lattice fluid theory. In particular, the sorption of carbon dioxide, water, and methanol is illustrated, exploiting the wealth of information gathered at a molecular level from Fourier-transform infrared (FTIR) spectroscopy to tailor thermodynamics modeling. The investigated penetrants display a different interacting characteristic with respect to the polymer substrate, which reflects itself in the sorption thermodynamics. For the specific case of water, the outcomes from molecular dynamics simulations are compared with the results of the present analysis.

In an effort to reduce the experimental tests required to characterize the mixed-gas solubility and solubility-selectivity of materials for membrane separation processes, there is a need for reliable models which involve a minimum number of adjustable parameters. In this work, the ability of the Dual Mode Sorption (DMS) model to represent the sorption of CO2/CH4 mixtures in three high free volume glassy polymers, poly(trimethylsilyl propyne) (PTMSP), the first reported polymer of intrinsic microporosity (PIM-1) and tetrazole-modified PIM-1 (TZ-PIM), was tested. The sorption of gas mixtures in these materials suitable for CO2 separation has been characterized experimentally in previous works, which showed that these systems exhibit rather marked deviations from the ideal pure-gas behavior, especially due to competitive effects. The accuracy of the DMS model in representing the non-idealities that arise during mixed-gas sorption was assessed in a wide range of temperatures, pressures and compositions, by comparing with the experimental results available. Using the parameters obtained from the best fit of pure-gas sorption isotherms, the agreement between the mixed-gas calculations and the experimental data varied greatly in the different cases inspected, especially in the case of CH4 absorbed in mixed-gas conditions. A sensitivity analysis revealed that pure-gas data can be represented with the same accuracy by several different parameter sets, which, however, yield markedly different mixed-gas predictions, that, in some cases, agree with the experimental data only qualitatively. However, the multicomponent calculations with the DMS model yield more reliable results than the use of pure-gas data in the estimation of the solubility-selectivity of the material.

Sorption data of nitrogen, argon and krypton in different glassy polymers at different cryogenic temperatures are analyzed, including hydrogen in PIM-1; conventional and high free volume glassy polymers are included. A consistent interpretation of experimental data is obtained by considering penetrant dissolution in a uniform dense glassy polymer, undergoing volume swelling with all penetrants but hydrogen. All the data are properly described by using the NELF model which is appropriate for the solubility in glassy polymers. Remarkably, in each polymer the sorption isotherms of different penetrants are described well by using the same initial polymer density, and the same swelling coefficient value allows satisfactory description of the sorption behavior of one penetrant at different temperatures. For PIM-1, NELF model and molecular dynamics give exactly the same swelling, and desorption after sorption or subsequent sorption-desorption cycles show hysteresis effects clearly associated to irreversible volume changes; in addition, hydrogen sorption in PIM-1 is fully predicted by the NELF model, simply based on nitrogen sorption, as opposed to BET theory. On the bases of the above results the conclusion is drown that BET theory is not applicable to the cryogenic sorption isotherms in glassy polymers. [ABSTRACT FROM AUTHOR]

Crazing is the common reason in polymer composites to cause failure. So far research work on craze phenomenon has been done only in homogenous polymer materials. The first time in our current study, the stress analysis has been carried out on the interaction between a circular inclusion and a full craze in polymer composites. A craze can be treated as a crack with fibrils bridging the two crack surfaces. The forces applied by the bridging fibrils to the crack surfaces (pulling the two surfaces closer) depend on the crack opening displacement, while the crack opening displacement is directly related on the forces applied by the bridging fibrils. To solve this dilemma, an iterative procedure is created and introduced to solve the formulated singular integral equations. The influences of the inclusion's elastic properties on the craze thickness profile and the stress intensity factors are investigated in details. It is found that the case with a “stiffer” inclusion produces smaller craze thickness. Also, the craze thickness profile is strongly affected by the inclusion size and the craze-inclusion distance. The shielding effect of a stiffer inclusion on the craze is discussed by evaluating the stress intensity factors at both craze tips. [ABSTRACT FROM AUTHOR]

Solubility and permeability of gases in glassy polymers have been considered with the aim of illustrating the applicability of thermodynamically-based models for their description and prediction. The solubility isotherms are described by using the nonequilibrium lattice fluid (NELF) (model, already known to be appropriate for nonequilibrium glassy polymers, while the permeability isotherms are described through a general transport model in which diffusivity is the product of a purely kinetic factor, the mobility coefficient, and a thermodynamic factor. The latter is calculated from the NELF model and mobility is considered concentration-dependent through an exponential relationship containing two parameters only. The models are tested explicitly considering solubility and permeability data of various penetrants in three glassy polymers, PSf, PPh and 6FDA-6FpDA, selected as the reference for different behaviors. It is shown that the models are able to calculate the different behaviors observed, and in particular the permeability dependence on upstream pressure, both when it is decreasing as well as when it is increasing, with no need to invoke the onset of additional plasticization phenomena. The correlations found between polymer and penetrant properties with the two parameters of the mobility coefficient also lead to the predictive ability of the transport model. [ABSTRACT FROM AUTHOR]