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The transformation of elliptical polarization in a layer of azobenzene-containing amorphous polymer is calculated. The dependences of the Stokes parameters for the propagation of a light wave deep into the layer are obtained. It is shown that the light-induced change in absorption leads to a decrease in the ellipticity of the light wave, which, in turn, slows down the rotation of the polarization ellipse. The obtained results are important for optical writing of phase structures in polymers. [ABSTRACT FROM AUTHOR]

Amorphous polymer‐based materials combining high optical transparency, mechanical flexibility, and the potential for low‐cost scalability and processing, are attractive in the vibrant field of ultralong organic phosphorescence (UOP). However, developing amorphous polymer‐based UOP materials with high quantum efficiency (ФP) remains a formidable challenge because the inherently loose polymer networks lead to the violent non‐radiative transition and quenching processes of triplet excitons. Herein, a series of amorphous polymer‐based UOP materials are fabricated by doping organic phosphors (SA, DA, and TA) composed of triphenylamine units modified with different numbers of carboxyl groups into polyvinyl alcohol (PVA) matrix. These experimental and computational results indicate that the resulting polymer films (SA/PVA, DA/PVA, and TA/PVA) exhibit the gradually enhanced UOP, which is attributed to the increased intermolecular hydrogen‐bonded interactions, enabling incremental repulsive interactions between the isolated chromophores and PVA matrix, resulting in the reduced dissipation of triplet excitons through a non‐radiative transition. Remarkably, TA/PVA has an optimal ФP of up to 77.5%, which is a record ФP among the reported heavy‐atom‐free amorphous polymer‐based UOP materials. Given the bright afterglow emission and solution‐processable properties, the promise of transparent, flexible, and large‐area paints for display and illumination are demonstrated. This study will provide a design strategy to enhance the quantum efficiency of amorphous phosphorescent materials, showing great promise in flexible electronics. [ABSTRACT FROM AUTHOR]

Three polymeric materials; polystyrene (amorphous), low-density polyethylene (semi-crystalline), and poly(methyl methacrylate) (amorphous) were used to explore their behavior and properties during processing using a co-rotating twin-screw extruder. Injection molding and compression molding were used for preparing the test specimens. Screw speed and barrel set temperatures were considered as the main processing variables while observing the process energy consumption of the extruder. The tensile, thermal, and rheological properties of the extruded materials under different processing conditions were evaluated. Test results confirmed that the motor power of the extruder for processing polystyrene and low-density polyethylene increased with increasing screw speed and decreased with increasing barrel set temperatures. Motor power for processing poly(methyl methacrylate) increased significantly with increasing screw speed. The total power consumption of the barrel heaters for processing polystyrene and low-density polyethylene slightly increased with the barrel set temperatures. The tensile modulus of polystyrene decreased with increasing screw speed at higher barrel set temperatures, while low-density polyethylene showed no significant variation. The tensile modulus of poly(methyl methacrylate) did not exhibit a clear trend with the extruder process settings. The effect of process settings on the glass transition temperature and melting temperature of the polymers was not significant, and no evidence was found of any molecular degradation during processing. Rheological properties of poly(methyl methacrylate) showed a significant variation with increasing screw speed and barrel set temperatures, while those of polystyrene and low-density polyethylene did not exhibit a consistent variation.

Three polymeric materials; polystyrene (amorphous), low-density polyethylene (semi-crystalline), and poly(methyl methacrylate) (amorphous) were used to explore their behavior and properties during processing using a co-rotating twin-screw extruder. Injection molding and compression molding were used for preparing the test specimens. Screw speed and barrel set temperatures were considered as the main processing variables while observing the process energy consumption of the extruder. The tensile, thermal, and rheological properties of the extruded materials under different processing conditions were evaluated. Test results confirmed that the motor power of the extruder for processing polystyrene and low-density polyethylene increased with increasing screw speed and decreased with increasing barrel set temperatures. Motor power for processing poly(methyl methacrylate) increased significantly with increasing screw speed. The total power consumption of the barrel heaters for processing polystyrene and low-density polyethylene slightly increased with the barrel set temperatures. The tensile modulus of polystyrene decreased with increasing screw speed at higher barrel set temperatures, while low-density polyethylene showed no significant variation. The tensile modulus of poly(methyl methacrylate) did not exhibit a clear trend with the extruder process settings. The effect of process settings on the glass transition temperature and melting temperature of the polymers was not significant, and no evidence was found of any molecular degradation during processing. Rheological properties of poly(methyl methacrylate) showed a significant variation with increasing screw speed and barrel set temperatures, while those of polystyrene and low-density polyethylene did not exhibit a consistent variation. [ABSTRACT FROM AUTHOR]

Shape memory polymers are a typical class of smart materials with wide potential applications. Mathematically modeling their thermomechanical behaviors with both simplicity and accuracy is challenging. In this work, a time‐varying viscosity model was introduced to investigate amorphous thermoset‐based shape memory polymers, with a special focus on recovery behaviors. This model employs only a varying viscosity to describe both the mechanism of strain storage and release during the shape memory cycle and the modulus‐temperature trend, along with a phenomenological description for the structural transition. Furthermore, the model effectively captures the effect of temperature rates and load conditions on recovery behaviors by tracking the evolution of parameter τ. This parameter shares the same dimension as time and serves as a phenomenological indicator of the chain mobility. Moreover, the parameter τ exhibits similar values among diverse materials at a specific characteristic temperature, providing a simple way to estimate the extent of recovery. Highlights: Introduced a simple phenomenological model to reproduce recovery behaviors and depict the modulus‐temperature trend.Both simulation and prediction results exhibit good agreement with tests.Effects of heating rates and load conditions can be traced by the model.The key model parameter τ possesses engineering and physical significance. [ABSTRACT FROM AUTHOR]

The intermolecular forces are of great importance to scientists in a wide field of disciplines as the progress of interactions between molecules determines the bulk properties of substances. It is a matter of fact that the approximation of thermodynamic and transport properties of polymers requires a realistic intermolecular potential associated with the topological constraints of the matter, namely the specific one‐to‐one secondary interactions between molecular groups. The out‐of‐equilibrium volume relaxation in glassy polymers remains confined to the phenomenological observation of bulk properties. The Lennard‐Jones (LJ)‐type potentials and the Tait equation are compared in this communication. It is shown that the subtle relaxation responses observed in glassy polymers can be suitably described using both the local (LJ) interactions and the phenomenological Tait equation for bulk behavior. The approach is based on the oversimplified assumption that the volume relaxation phenomena are the isotropic manifestation of random relaxations of local directional interactions of secondary bonds. The results appear surprisingly appealing, given the straightforward approach. [ABSTRACT FROM AUTHOR]

We report an experimental study of the self-action of TEM01 and TEM00 Gaussian modes in a layer of a comb-shaped amorphous polymer with cyanobiphenyl and azobenzene side fragments. For the linearly polarized TEM01 mode, a pattern of aberration self-action is observed in the form of rings with an additional system of the fringes, caused by interference from two intensity peaks. The position of the fringes and the microscopic image of the deformation region correspond to the local nature of the nonlinear optical response. For the circularly polarized (with an ellipticity of about 7%) TEM00 Gaussian mode, the polarization of the outer aberration ring is close to linear. This effect stems from the self-rotation of the polarization ellipse due to the manifestation of Kerr-type nonlinearity. A characteristic feature of this effect in an amorphous polymer is an increase in the eccentricity of the ellipse (transformation of circular polarization into linear polarization), which is caused by a light-induced change in the orientation distribution function of the chromophores. [ABSTRACT FROM AUTHOR]

One of the important problems of the modern rheology of polymer materials, namely, the possibility of describing the deformation of amorphous polymers within the framework of linear rheological relationships between relative deformation and deforming stress or the need to use nonlinear rheological equations is considered. The criteria for distinguishing these approaches, namely, the determination of the corresponding critical values of the macro- and microphysical characteristics of the material and the conditions for carrying out the mechanical tests are also discussed. In particular, the difference between the influence of kinetic and thermodynamic nonlinear effects on the regularities of deformation processes of amorphous polymers in warm and frozen states was noted. The influence of nonlinear effects on the general shape and characteristics of individual stages of the "relative strain - deforming stress" diagram at deformation of polymer samples with specified values of strain rate and temperature is analyzed in detail. The results of the theoretical analysis were used for the physical interpretation of the general form and features of individual stages of the tensile test diagrams of amorphous polyimide films (V. D. Natsik, H. V. Rusakova, S. V. Lubenets, V. A. Lototskaya, and L. F. Yakovenko, Fiz. Nyzk. Temp. 49, 569 (2023) [Low Temp. Phys. 49, 521 (2023)]), empirical estimates for the rheological characteristics of this polymer were obtained. [ABSTRACT FROM AUTHOR]

[Display omitted] The self-diffusion coefficient of active ingredients (AI) in polymeric solid dispersions is one of the essential parameters for the rational formulation design in life sciences. Measuring this parameter for products in their application temperature range can, however, be difficult to realise and time-consuming (due to the slow kinetics of diffusion). The aim of this study is to present a simple and time-saving platform for predicting the AI self-diffusivity in amorphous and semi-crystalline polymers on the basis of a modified version of Vrentas' and Duda's free volume theory (FVT) [A. Mansuri, M. Völkel, T. Feuerbach, J. Winck, A.W.P. Vermeer, W. Hoheisel, M. Thommes, Modified free volume theory for self-diffusion of small molecules in amorphous polymers, Macromolecules. (2023)]. The predictive model discussed in this work requires pure-component properties as its input and covers the approximate temperature range of T < 1.2 T g , the whole compositional range of the binary mixtures (as long as a molecular mixture is present), and the whole crystallinity range of the polymer. In this context, the self-diffusion coefficients of the AIs imidacloprid, indomethacin, and deltamethrin were predicted in polyvinylpyrrolidone, polyvinylpyrrolidone/vinyl acetate, polystyrene, polyethylene, and polypropylene. The results highlight the profound importance of the kinetic fragility of the solid dispersion on the molecular migration; a property which in some cases might entail higher self-diffusion coefficients despite an increase in the molecular weight of the polymer. We interpret this observation within the context of the theory of heterogeneous dynamics in glass-formers [M.D. Ediger, Spatially heterogeneous dynamics in supercooled liquids, Annu. Rev. Phys. Chem. 51 (2000) 99–128] by attributing it to the stronger presence of "fluid-like" mobile regions in fragile polymers offering facilitated routes for the AI diffusion within the dispersion. The modified FVT further allows for identifying the influence of some structural and thermophysical material properties on the translational mobility of AIs in binary dispersions with polymers. In addition, estimates of self-diffusivity in semi-crystalline polymers are provided by further accounting for the tortuosity of the diffusion paths and the chain immobilisation at the interface of the amorphous and crystalline phases. [ABSTRACT FROM AUTHOR]

An increasing number of high-performing gas separation membranes is reported almost on a daily basis, yet only a few of them have reached commercialisation while the rest are still considered pure research outcomes. This is often attributable to a rapid change in the performance of these separation systems over a relatively short time. A common approach to address this issue is the development of mixed matrix membranes (MMMs). These hybrid systems typically utilise either crystalline or amorphous additives, so-called fillers, which are incorporated into polymeric membranes at different loadings, with the aim to improve and stabilise the final gas separation performance. After a general introduction to the most relevant models to describe the transport properties in MMMs, this review intends to investigate and discuss the main advantages and disadvantages derived from the inclusion of fillers of different morphologies. Particular emphasis will be given to the study of the compatibility at the interface between the filler and the matrix created by the two different classes of additives, the inorganic and crystalline fillers vs. their organic and amorphous counterparts. It will conclude with a brief summary of the main findings. [ABSTRACT FROM AUTHOR]

A comprehensive experimental and theoretical study of the regularities of active deformation at a constant rate of an amorphous polymer at room temperature and the influence of moderate and deep cooling on them was performed. The samples of amorphous aromatic polyimide (an analogue of kapton H) that are randomly cut fragments of the industrially produced thermoplastic film with a thickness of 25 μm were the object of the experimental study. The σ–ε diagrams of the tensile test, where σ and ε = ε ˙ t are the tensile stress and the relative strain, respectively, were recorded for 32 samples at three rates ε ˙ = 7⋅10–5, 7⋅10–4, 6⋅10–3 s–1 under three temperatures T = 293, 77, and 4.2 K. In the state of deep cooling at T = 4.2 K, several samples were deformed as brittle glassy bodies – rupture after short elastic deformation. But the majority of the samples at all values of the experimental parameters (T , ε ˙) had the rheological properties of rubber-like highly elastic materials (elastomers) with traditional tensile test diagrams: initial stage I of linear elastic deformation σ I = M e ε with Young's modulus M e = M e (T) ; stage III of linear highly elastic deformation σ III = σ f e + M h e ε with modulus M h e = M h e (T) and conditional limit of elasticity σ f e = σ f e (T , ε ˙) ; intermediate stage II of the relaxation type σ II (ε ; T , ε ˙) with a nonlinear stress-strain dependence. The σ–ɛ diagrams of the individual samples with sufficiently high accuracy coincide with the graph of the function σ (ε ; T , ε ˙) which is the solution of the previously derived nonlinear rheological equation (V. D. Natsik and H. V. Rusakova, Fiz. Nizk. Temp.48, 281 (2022) [Low Temp. Phys.48, 253 (2022)]; Fiz. Nyzk. Temp.49, 246 (2023) [Low Temp. Phys.49, 228 (2023)]). In its derivation, a molecular-kinetic model was used: an amorphous polymer is considered as a set of statistically independent kinetic units, namely, molecular segments, and the elementary act of deformation is caused by thermomechanical activation of nonlinear excitations of these segments called elastons. The elaston mechanism of transformation of the deformation diagrams of amorphous polyimide samples under their moderate and deep cooling is discussed in detail: the transition between deformation states of warm and frozen elastomer, low-temperature effects of structural-deformation glass transition and deformation melting. Comparing the results of experiments and theory made it possible to obtain the empirical estimates for the macromechanical characteristics of the studied samples and the microparameters of elaston excitations. A significant and unsystematic (random) scatter of the macro- and micromechanical characteristics of the samples was revealed, which indicates a significant and random heterogeneity of the macro- and microstructure of the polyimide film from which they were made. [ABSTRACT FROM AUTHOR]

Four model polymers, representing (i) amorphous homopolymers (Kollidon K30, K30), (ii) amorphous heteropolymers (Kollidon VA64, KVA), (iii) semi-crystalline homopolymers (Parteck MXP, PXP), and (iv) semi-crystalline heteropolymers (Kollicoat IR, KIR), were examined for their effectiveness in creating posaconazole-based amorphous solid dispersions (ASDs). Posaconazole (POS) is a triazole antifungal drug that has activity against Candida and Aspergillus species, belonging to class II of the biopharmaceutics classification system (BCS). This means that this active pharmaceutical ingredient (API) is characterized by solubility-limited bioavailability. Thus, one of the aims of its formulation as an ASD was to improve its aqueous solubility. Investigations were performed into how polymers affected the following characteristics: melting point depression of the API, miscibility and homogeneity with POS, improvement of the amorphous API's physical stability, melt viscosity (and associated with it, drug loading), extrudability, API content in the extrudate, long term physical stability of the amorphous POS in the binary drug–polymer system (in the form of the extrudate), solubility, and dissolution rate of hot melt extrusion (HME) systems. The obtained results led us to conclude that the physical stability of the POS-based system increases with the increasing amorphousness of the employed excipient. Copolymers, compared to homopolymers, display greater homogeneity of the investigated composition. However, the enhancement in aqueous solubility was significantly higher after utilizing the homopolymeric, compared to the copolymeric, excipients. Considering all of the investigated parameters, the most effective additive in the formation of a POS-based ASD is an amorphous homopolymer—K30. [ABSTRACT FROM AUTHOR]

We present calculation results of the temperature interval δTg characterizing the liquid–glass transition in amorphous materials obtained on the basis of available data of the empirical parameters C1 and C2 in the Williams–Landel–Ferry (WLF) viscosity equation. We consider the unambiguous dependence of the relative transition temperature interval δTg/Tg on the fraction of the fluctuation volume fg frozen at the glass transition temperature Tg utilizing Sanditov's model of delocalized atoms. The parameter f = ΔVe/V, which determines the molecular mobility characteristic of delocalized atoms in the liquid–glass transition region, is weakly dependent on the nature of most vitreous substances and can be found as fg = 1/C1. We show that the temperature interval δTg is less than 1% of the Tg for most amorphous substances. This result conforms with Simon's classical idea of a small temperature range in which the structure freezes. The structural relaxation time τg at Tg of polymers and chalcogenide glasses is also calculated. [ABSTRACT FROM AUTHOR]

The main goal of this work was to elucidate, for the first time, the applicability of Gaussian and Weibull statistical models to describe the distributions of the mechanical properties of quasi-brittle and ductile amorphous polymers and miscible blends thereof characterizing by tensile strength of common materials of order of 10–100 MPa. For this purpose, the distributions of tensile strength (σ), strain at break (ε), and Young's modulus (E) of polystyrene (PS), poly(2,6-dimethyl-1,4-phenylene oxide) (PPO), and two miscible blends thereof with different PS/PPO weight ratios (3/1 and 1/1) have been analyzed using the Gaussian and Weibull statistical models. It has been shown that the applicability of a chosen theoretical model to correctly describe the statistical distribution of a measured mechanical property was dependent on the property analyzed (σ, ε, or E), the sample brittleness [quasi-brittle PS (ε = 3%) and PS/PPO blends (ε = 4–5%) or ductile PPO (ε = 20%)], and the PPO content in the test samples. Scatter of the experimental data of σ, ε, and E for the four polymer systems investigated has been characterized with the Weibull modulus (m) calculated from the plots constructed in specific coordinates "loglog(function of fracture probability) − log(property)." The calculated values of m for PS, PPO, and PS/PPO blends have been compared with those reported in the literature for ultra-high-strength materials of various natures (σ > 1 GPa) and low-strength polymer–polymer interfaces (σ < 1 MPa), and similarities and differences found have been discussed. [ABSTRACT FROM AUTHOR]

The effect of temperature variations over a wide range on the rheological properties of amorphous polymers with high rubber-like elasticity (elastomers) is discussed. A theoretical study of the transition from the deformation state of a warm elastomer to the state of a frozen one, the effects of structural-strain glass transition and forced elasticity was done. Two types of mechanical testing of polymer samples are considered in detail: slow tensile deformation at a constant rate and relaxation of the deforming stress after deformation stops. The study was carried out on the basis of the previously proposed molecular-kinetic model of the processes of highly elastic deformation of amorphous polymers and the corresponding nonlinear rheological equation (V. D. Natsik and H. V. Rusakova, Fiz. Nizk. Temp.48, 281 (2022) [Low Temp. Phys. 48, 253 (2022)]). [ABSTRACT FROM AUTHOR]

The amorphous polymers present remarkable temperature- and rate-dependent deformation behaviors. Based on a combination of the multiple relaxation viscoelastic-viscoplastic model and the three-element viscoelastic model, a constitutive model was constructed to describe the changes in mechanical properties of amorphous polymers from below to above glass transition temperature (θg). In this model, an exponential evolution equation of volume fraction was constructed to reflect the changes in glassy and rubbery phases at different temperatures. The proposed model was implemented into ABAQUS using the user-defined material subroutine (VUMAT). The strain-softening after yield and rate-dependent behaviors above and below θg were reasonably captured by the present model. Meanwhile, the creep and relaxation behaviors of the material were described. Finally, the processes of the tensile deformation of a dumbbell plate with a circular hole and the rate-dependent pressed film molding were simulated by the VUMAT. The results show that the implemented model can reasonably predict the structural responses of amorphous polymers.

The mesogen orientations of liquid crystals are sensitive to the nature of the contacting surface. For side chain liquid crystalline polymer (SCLCP) films, most investigations have been conducted for thin films formed on a solid substrate surface such as glass, quartz and metal oxides, and little knowledge has been accumulated for SCLCP films whose top surface is covered by amorphous polymers. This work presents the effect of a topcoat with amorphous polymers placed on SCLCP films on the mesogen orientation and photoalignment behavior. When an SCLCP film that adopts a homeotropic mesogen orientation is covered with a glass plate or polymer layer, the mesogens turns to a random planar orientation. This planar orientation is favorable for efficient in-plane photoalignment by irradiation with linear polarized light. An in-plane order parameter exceeding 0.5 is readily obtained. Unexpectedly, a significant stabilization of the liquid crystal phase by over 10 °C is observed above the isotropization temperature of the SCLCP. These fundamental sets of knowledge should be significant in the fabrication of various polymer LC devices. [ABSTRACT FROM AUTHOR]

Long‐lived room temperature phosphorescent (LRTP) materials have attracted widespread attention due to their unique luminescence phenomenon and application prospects in the fields of information encryption and bioimaging. However, achieving intelligent response LRTP from amorphous polymers under atmospheric conditions is fascinating but challenging. Here, a series of irradiation‐dependent LRTP systems with ultralong phosphorescent lifetime and high quantum yields are fabricated by a consuming triplet oxygen strategy, and the LRTP performance exhibits obvious chromophore structure and polymeric molecular weight dependence. By extending the UV irradiation time, the phosphorescence lifetime can be increased by hundreds of times, which can exceed 2 s. Experimental results prove that the molecular weight of the polymer matrix, the doping concentration, and the structure of the chromophore have a crucial influence on the stimulus‐response speed and phosphorescence properties of the materials. This kind of intelligent and irradiation‐dependent LRTP material has excellent application prospects in the field of multi‐level information encryption. This work will effectively promote the development of stimulus‐responsive LRTP materials under atmospheric conditions. [ABSTRACT FROM AUTHOR]

Ultralong room temperature phosphorescence is employed in information encryption, chemical sensing, lighting, and imaging on account of its long lifetime and high signal‐to‐noise ratio. As the triplet excitons can be easily quenched and interfered by nonradiative transition process, it is difficult to obtain long‐lived phosphorescence through conventional methods. Herein, a general design strategy to form cross‐linked networks by click chemistry is presented for efficiently promoting the phosphorescence performance. Using the hydrogen bonding interactions formed between CO···HN units and covalently cross‐linked network by the BO bond, the rigidity of the entire system is greatly enhanced, so the radiative transition process is well strengthened. Interestingly, under the influence of water molecule, the afterglow colors of the system change from blue (488 nm) to green (510 nm). Because of the presence of cross‐linked network, the emission is not directly quenched when the system is intervened by water. Having long phosphorescence lifetime (841.06 ms) and high quantum yield (10.48%), the obtained system is utilized for anti‐counterfeiting demonstration. This strategy paves a new way for the design of amorphous ultralong room temperature phosphorescence materials by efficient and user‐friendly click chemistry. [ABSTRACT FROM AUTHOR]

Molecular doping of conjugated polymers is the performance-determining step in the fabrication of organic thermoelectric devices. Although strongly oxidizing salt-type dopants effectively produce charge carriers in polymer chains, their poor solubility in the processing solvents leads to undesired precipitation and complicates the film fabrication process. Thus, it is important to develop a conjugated polymer that can be readily doped in a mixed solution using organic dopants. In this study, we synthesized amorphous but highly electronrich polymers (PCT1 and PCT2) by combining 4H-cyclopenta[2,1-b:3,4-b'] dithiophene and thieno[3,4-b]thiophene moieties, whose full-names are poly[(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b:3,4-b']dithiophene-2,6-diyl)-alt- (2-ethylhexyl-3-fluorothieno[3,4-b]thiophene-2-carboxylate 4,6-diyl)] (PCTs). The PCT polymers were heavily doped with the organic dopant 2,3,5, 6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), and the resulting PCT:F4TCNQ complex formed an integer charge transfer complex and promoted the intermolecular ordering of PCT polymers. Notably, the PCT: F4TCNQ complex exhibited unique thermoelectric behaviors, with significantly increased power factors even in the presence of large quantities of F4TCNQ, reaching values 3.2-fold higher than those achieved with FeCl3 sequential doping. Moreover, the higher-molecular-weight polymer, PCT2, exhibited more efficient molecular ordering and charge carrier transport than PCT1, which are crucial for enhancing the thermoelectric properties. [ABSTRACT FROM AUTHOR]

We conducted large-scale molecular dynamics (MD) simulations of shock wave propagation and spallation in amorphous polyurethane and polyurea. First, we computed the shock Hugoniot of the polymers using the multiscale shock technique and compared them with available experimental data to establish the upper limit of the shock pressure that can be accurately modeled using a non-reactive interatomic force field. Subsequently, we simulated shock wave propagation in the polymers, varying the shock particle velocity from 0.125 km/s to 2 km/s. A remarkable similarity in the shock behavior of polyurethane and polyurea was observed. The spall strength of each sample was computed by two methods: (a) the indirect method (based on the free surface velocity history)--accessible in experiments and (b) a direct method (based on the atomic stresses in the region of spallation)--accessible only through MD. The results reveal that the tensile strength computed from the indirect method is consistently smaller than the value obtained from the direct method. Moreover, the strength computed from the indirect method shows a noticeable agreement with the fracture nucleation stress. Our results provide novel molecular-level insights into the spallation mechanisms of amorphous polymers, which could facilitate the design of polymers for structural barrier applications. [ABSTRACT FROM AUTHOR]

We present calculation results of the temperature interval δTg characterizing the liquid–glass transition in amorphous materials obtained on the basis of available data of the empirical parameters C1 and C2 in the Williams–Landel–Ferry (WLF) viscosity equation. We consider the unambiguous dependence of the relative transition temperature interval δTg/Tg on the fraction of the fluctuation volume fg frozen at the glass transition temperature Tg utilizing Sanditov’s model of delocalized atoms. The parameter f = ΔVe/V, which determines the molecular mobility characteristic of delocalized atoms in the liquid–glass transition region, is weakly dependent on the nature of most vitreous substances and can be found as fg = 1/C1. We show that the temperature interval δTg is less than 1% of the Tg for most amorphous substances. This result conforms with Simon’s classical idea of a small temperature range in which the structure freezes. The structural relaxation time τg at Tg of polymers and chalcogenide glasses is also calculated.

The mesogen orientations of liquid crystals are sensitive to the nature of the contacting surface. For side chain liquid crystalline polymer (SCLCP) films, most investigations have been conducted for thin films formed on a solid substrate surface such as glass, quartz and metal oxides, and little knowledge has been accumulated for SCLCP films whose top surface is covered by amorphous polymers. This work presents the effect of a topcoat with amorphous polymers placed on SCLCP films on the mesogen orientation and photoalignment behavior. When an SCLCP film that adopts a homeotropic mesogen orientation is covered with a glass plate or polymer layer, the mesogens turns to a random planar orientation. This planar orientation is favorable for efficient in-plane photoalignment by irradiation with linear polarized light. An in-plane order parameter exceeding 0.5 is readily obtained. Unexpectedly, a significant stabilization of the liquid crystal phase by over 10 °C is observed above the isotropization temperature of the SCLCP. These fundamental sets of knowledge should be significant in the fabrication of various polymer LC devices.

A copolymer of perfluoro-2-ethyl-2-methyldioxole and perfiuoropropyl vinyl ether was prepared by the method of high-pressure polymerization. The synthesized polymer has high optical transparency, a low refractive index, and a low material dispersion in the telecommunication wavelength ranges near 0.85, 1.3, and 1.5 µm. In addition, the polymer is predominantly amorphous and has high glass-transition and decomposition temperatures. The synthesized polymer is able to film formation and promising for the design and construction of high-speed optoelectronic printed circuit boards in which a metallic conductor-based electrical data bus is supplemented with an optical data bus based on a polymeric waveguide array. Films with a thickness of 4–8 µm were fabricated from the synthesized polymer by centrifuging. The polymer was characterized by DSC, DTGA, TMA, X-ray diffraction analysis (XRD), and IR spectroscopy. [ABSTRACT FROM AUTHOR]

In our previous study, electrically induced mechanical stress was produced on monolithic polycarbonate (PC) films under a DC voltage using a needle‐plane electrode setup. This study investigated other materials with various structures and dielectric constants, in order to further understand the deformation mechanism. It was found that the elastic behavior occurred at electric fields intensities below that initiating measurable surface deformation. The amorphous materials, PS, and the semi‐crystalline materials, HDPE and PP, having dielectric constants all around 2.5, exhibited a similar observable deformation onset electric field at 200 MV/m. While PVDF, having a dielectric constant of 10.0–12.0, showed an onset at only 30 MV/m. The data was also compared to our previous study on PC. The depth and diameter of the deformation for all materials increased relative to the applied electric field up to film breakdown. Thermal annealing of the deformed films revealed a recoverable "delayed elastic" component and an irreversible "plastic" component. A three‐stage electrically induced mechanical deformation mechanism was proposed for amorphous materials, while a two‐stage mechanism was proposed for the semi‐crystalline materials. The difference on the energy loss versus deformed volume for amorphous and semi‐crystalline polymers was also determined and discussed. [ABSTRACT FROM AUTHOR]

A physically-based constitutive model for predicting the mechanical response of amorphous glassy polymers at room temperature and low strain rates was established within the frame of thermodynamics and kinematics. In our previous work (Lan et al., 2022b), the concepts of permanent entanglement (PE) and dynamic entanglement (DE) were utilized to reproduce the complicated behavior of amorphous glassy polymers from quasi-static to dynamic loading at temperatures from below to near the glass transition temperature. PE formed by the coiling of macromolecular chains is relatively stable and contributes to the yield and unloading behavior. DE formed by the weak interaction between monomers of adjacent segments is unstable and contributes to the macroscopic yield peak and strain hardening. However, due to including many parameters, the model is not easy to apply in practice. In this work, by ignoring the influence of temperature, the previous model (Lan et al., 2022b) was simplified. Taking polycarbonate (PC) and polystyrene (PS) as examples, the simplified model focused on the macroscopic mechanical behavior under simple compression and cyclic simple compression, analyzed the effects of mesh and specimen size on the evolution of shear bands under plane strain compression, and compared the obvious differences in localized deformation of these two types of amorphous polymers under plane strain compression. In addition, the forging process of PC at room temperature was simulated. By comparing the predictions with the experiments, it is demonstrated that the simplified model can reproduce the macroscopic mechanical response of amorphous polymers under simple compression, cyclic simple compression, plane strain compression and forging. • Based on thermodynamics a physically-based model is developed. • The evolution of shear bands in PS under plane strain compression is discussed. • The model can predict the mechanical behavior under different loading conditions. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the time–temperature correlation of amorphous thermoplastics at large strains based on coarse-grained molecular dynamics simulations. This correlation behavior is characterized by the strain hardening modulus in uniaxial tension simulations at different strain rates across the glass transition region. The temperature regime is divided into a melt zone, a glassy zone, and a transition zone between them, according to the storage modulus calculated from dynamic mechanical analysis (DMA) at small strains. In the melt zone, the existence of time–temperature superposition (TTS) at large strains is verified by constructing a master curve of the hardening modulus. The obtained shift factors are then compared to those from DMA at small strains, showing that the TTS behavior is transferable between small and large strains. In the glassy zone, the effects of time and temperature are not superposable at large strains but still can be correlated. To demonstrate this correlation behavior, we introduce a level set of the hardening modulus with a variable pair of strain rate and temperature. Pairs lying in the same level result in coincident stress–strain curves at large strains. The transferability of the correlation behavior between large and small strains is validated by comparing these stress–strain curves at small strains in the pre-yield region. In the transition zone, the correlation behavior is studied with both aforementioned methods, showing that TTS is applicable to large strains but not transferable to small strains. Finally, we propose a phenomenological constitutive model for uniaxial tension to demonstrate the time–temperature correlation at large strains, considering different constant strain rates and temperatures. • The time–temperature superposition (TTS) is observed at large strains above T g. • The time and temperature are observed to be correlated at large strains below T g. • The transferability of the correlation is observed between small and large strains. • A phenomenological constitutive model for this correlation behavior is proposed. [ABSTRACT FROM AUTHOR]

Following the growing use of amorphous polymers in an expanding range of applications, interest for numerical modeling of polymer behavior has greatly increased. Together with reliable constitutive models, stable, accurate and rapid integration algorithms valid for large deformations need to be developed. Here, in the framework of hyperelasto-viscoplasticity and multiplicative split formulation, three integration algorithms (explicit, fully implicit and forward gradient) are generated for a constitutive polymer model and respective stability is investigated. The algorithms are furthermore implemented in a commercial Finite Element code and simulation of a full field tensile test is shown to capture the actual deformation behavior of polymers. [ABSTRACT FROM AUTHOR]

Highlights • Effect of temperature and strain rate on the yield stress of amorphous polymers. • Thermodynamic analysis of Argon's model for the yield stress of polymers. • Use of elastic modulus approaches for the effect of temperature and strain rate. • Extended range of predictive capability of Argon's model. Abstract In amorphous polymers, the yield stress is strongly dependent on strain rate and temperature. It is demonstrated that the influence of strain rate and temperature can be studied from a thermodynamic point of view by defining activation parameters. These parameters allow for understanding the mechanisms that take place during plastic yielding. A comparative study based on this thermodynamic framework is conducted on the classical Argon's model for the yield stress. Different cases are investigated using different expressions of the elastic modulus as a parameter of this model: constant Young's modulus value, temperature dependent Young's modulus and temperature-and-strain-rate dependent Young's modulus. The corresponding activation parameters are derived and analysed for a wide range of temperatures and strain rates. The numerical predictions are also compared with experimental data taken from the literature. This analysis shows that the validity of Argon's model can be extended to dynamic strain rates and to higher temperature (up to the glass transition) when combined with appropriate models for the elastic modulus for these ranges of strain rates and temperatures. [ABSTRACT FROM AUTHOR]

Weathering-induced polymer degradation is typically heterogeneous which plays an integral part in fragmentation. Despite that, the current selection of techniques to investigate such heterogeneities, especially beneath the sample surface, is sparse. We introduce Laser-induced Breakdown Spectroscopy (LIBS) as an analytical tool and evaluate its performance for depth profiling. Three types of polymers were selected (polyethylene, polypropylene, and polystyrene) that were aged under controlled conditions. We demonstrate that LIBS can detect heterogeneous oxidation on the surface and inside the samples. The results reveal that different oxidation behaviors are linked to the sample's lattice structure and the subsequent formation of microcracks. This implies that LIBS is beneficial to give additional insights into the weathering and degradation behavior of environmentally relevant plastics. [Display omitted] • Heterogeneous plastic degradation is related to the plastic's lattice structure. • Degradation processes should be studied over the entire sample volume. • LIBS can conduct three-dimensional chemical mapping without exposing the cross-section. • PE, PP and PS samples have been studied for different weathering times. [ABSTRACT FROM AUTHOR]

Abstract Laser transmission welding is widely used for the creation of strong, hermetic and optically appealing joints between thermoplastic parts. Amorphous polymers like polycarbonate and poly(methyl methacrylate) offer excellent optical properties, making them suitable for this joining technique and especially attractive for lighting and decorative applications, for example in the automotive industry. However, the rapid and non-uniform temperature changes during the process can lead to residual stresses, which can impair weld strength and result in part failure due to environmental stress cracking. In this work it was found, that the application of 2 µm laser radiation can lead to reduced stress-cracking-susceptibility compared to conventional laser transmission welding with wavelengths of ~1 µm. [ABSTRACT FROM AUTHOR]

Abstract: Pure organic, heavy‐atom‐free room‐temperature phosphorescence (RTP) materials have attracted much attention and have potential applications in photoelectric and biochemical material fields owing to their rich excited state properties. They offer long luminescent lifetime, diversified design, and facile preparation. However, recent achievements of efficient phosphorescence under ambient conditions mainly focus on ordered crystal lattices or embedding into rigid matrices, which require strict growth conditions and have poor reproducibility. Herein, we developed a concise approach to give RTP with a decent quantum yield and ultralong phosphorescence lifetime in the amorphous state by radical binary copolymerization of acrylamide and different phosphors with oxygen‐containing functional groups. The cross‐linked hydrogen‐bonding networks between the polymeric chains immobilize phosphors to suppress non‐radiative transitions and provide a microenvironment to shield quenchers. [ABSTRACT FROM AUTHOR]

The present study describes comparative results obtained experimentally on two polymeric surfaces during contacts with a rigid spherical indenter. An experimental setup specifically dedicated to transparent materials has been used to analyze the creep phenomenon over long holding time segments (10 5 s) and to study the recovery process once contact has been removed. As a function of imposed contact time, a normalized value of representative strain is defined to quantify creep and recovery steps. Experimental results indicate that the recovery of the deformed surface after contact is mainly dependent on the initial contact time. Finite Elements Modeling will be used to discuss further the time-depending behaviors of the materials. [ABSTRACT FROM AUTHOR]

The structural response of amorphous elastomers to applied pressure and temperature is of significant interest given their potential for blast and impact protection applications. While understanding disordered structures is often challenging, this study focuses on the ordered correlations that are present at the atomic level even in amorphous materials. This local order was characterized in polyurea elastomers with two molecular weights up to 6 GPa and ∼280 °C using in situ energy dispersive X-ray diffraction at the Advanced Photon Source via total scattering techniques. The resulting structure factors and pair distribution functions indicate that the applied pressure reduced the free volume but had little effect on covalent bonds for both molecular weights. Temperature-induced order-disorder transitions that occur readily at ambient pressures within the temperature range studied here were not observed, their onset likely delayed by the limited chain mobility associated with the free volume reduction. This study demonstrates that total scattering offers insights into the high-pressure structure of disordered polymers that are otherwise inaccessible using more conventional X-ray scattering techniques. [Display omitted] • Atomic structure of polyurea studied at 6 GPa, 280 °C via total X-ray scattering. • Structural response was identical for two different molecular weights. • Applied pressure reduced free volume with little impact on covalent bonding. • Restricted chain mobility prevented temperature-induced transitions at 6 GPa. • Molecular dynamics simulations used to analyze and interpret the experimental data. [ABSTRACT FROM AUTHOR]

In this paper, a recently proposed finite strain visco-elastic visco-plastic (three-dimensional) constitutive model is extended to predict the nonlinear response of amorphous polymers from low to high strain rates. The model accounts for the influence of distinct molecular mechanisms, which become active at different deformation rates. Therefore, the constitutive equations include two relaxation phenomena to describe the strain rate sensitivity of amorphous polymers. Well-established rheological elements are adopted to define visco-elasticity (generalized Maxwell elements) and visco-plasticity (Eyring dashpots). In addition, strain hardening is modeled with a plasticity-induced (nonlinear) hardening element which is extended to distinguish between the contribution of the two transitions. From a computational viewpoint, a fully implicit integration algorithm is derived, and a highly efficient implementation is obtained. It is shown that it is possible to reduce the return mapping system of equations to only two independent (scalar) nonlinear equations. A four-stage optimization-based calibration procedure is proposed to identify the model's material parameters in a completely unsupervised way. The predictive capability of the constitutive model is validated against literature results for polycarbonate and poly(methyl methacrylate), accounting for temperature and strain rate dependencies under different loading conditions. The results show that the model can capture the transition in the yield behavior and predict the post-yield large strain behavior over a wide range of strain rates. The efficiency of the calibration procedure and the overall numerical strategy is also demonstrated. Despite the adiabatic conditions observed under high strain rates, the model replicates the associated effect of temperature through strain rate dependency. • A visco-elastic visco-plastic constitutive model is formulated from low to high strain rates. • Two molecular mobility mechanisms are modeled with known rheological elements. • A fully implicit formulation is derived leading to an efficient implementation. • A four-stage optimization-based calibration procedure is proposed. • Excellent agreement with experimental and numerical results for two thermoplastics. [ABSTRACT FROM AUTHOR]

The comparative analysis of gas transport properties and conformational parameters of membranes obtained from two polyimides and polysulfone was made. It was shown that the introduction of a sulfone group instead of a methylene group in the amine component of polyimide leads to an increase in glass transition temperature and of polymer membrane permeability coefficient and a reduction in selectivity. Also it was demonstrated that the solvent used during the preparation of polymer membranes had a significant influence on their gas transport characteristics. [ABSTRACT FROM AUTHOR]

ABSTRACT The mechanical loading induced flow of glassy polymers is triggered by the nucleation of shear transformation units, and strongly depends on the initial microstructural state of the material. Therefore, investigation of the possible relationship between the microstructural state variables and plastic deformation is required for a better understanding of the macroscopic response of this class of materials during large deformation. In this study, free volume content is considered as a state variable and thermal treatment is selected as a process through which the accelerated and forced evolution of the free volume can be imposed. For two well-known glassy polymers, poly(methyl methacrylate) and polycarbonate, the free volume content alteration upon annealing is monitored via positron annihilation spectroscopy, and the changes of the micro- and macromechanical properties are also obtained by utilizing nanoindentation technique and employing the homogeneous amorphous flow theory. The correlation between the microstructural state variable, that is, free volume, and the micromechanical state variable, that is, shear activation volume, is then investigated. The results reveal opposite direction of alterations of free volume and shear activation volume with annealing temperature. Accordingly, the possibility of the existence of an interrelation between these two state variables is critically discussed. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 1286-1297 [ABSTRACT FROM AUTHOR]

Due to their high deformation capabilities, polymeric materials are widely used in several industries. However, polymers exhibit a complex behaviour with strain rate, temperature and pressure dependencies. Numerous constitutive models were developed in order to take into account their specific behaviour. Among these models, the ones proposed by Richeton et al Polymer 46:6035-6043 (2005a), Polymer 46:8194-8201 (2005b) seem to be particularly suitable. They proposed expressions for the Young modulus and the yield stress with strain rate and temperature dependence. Moreover, these models were also implemented in a finite elastic-viscoplastic deformation approach using a flow rule based on thermally activated process. The increase of computational capabilities allowed simulating polymer forming processes using finite element (FE) codes. The aim of the study is to implement the proposed constitutive model in a commercial FE code via a user material subroutine. The implementation of the model was verified using compressive tests over a wide range of strain rates. Next, FE simulations of an impact test and of a plane strain forging process were carried out. The FE predictions are in good agreement with the experimental results taken from the literature. [ABSTRACT FROM AUTHOR]

This document defines terms relating to the properties of individual macromolecules, macromolecular assemblies, polymer solutions, and amorphous bulk polymers. In the section on polymer solutions and amorphous bulk polymers, general and thermodynamic terms, dilute solutions, phase behaviour, transport properties, scattering methods, and separation methods are considered. The recommendations are a revision and expansion of the IUPAC terminology published in 1989 dealing with individual macromolecules, macromolecular assemblies, and dilute polymer solutions. New terms covering the principal theoretical and experimental developments that have occurred over the intervening years have been introduced. Polyelectrolytes are not included. [ABSTRACT FROM AUTHOR]

This document defines terms relating to the properties of individual macromolecules, macromolecular assemblies, polymer solutions, and amorphous bulk polymers. In the section on polymer solutions and amorphous bulk polymers, general and thermodynamic terms, dilute solutions, phase behaviour, transport properties, scattering methods, and separation methods are considered. The recommendations are a revision and expansion of the IUPAC terminology published in 1989 dealing with individual macromolecules, macromolecular assemblies, and dilute polymer solutions. New terms covering the principal theoretical and experimental developments that have occurred over the intervening years have been introduced. Polyelectrolytes are not included. [ABSTRACT FROM AUTHOR]

In this article, we propose an approach suitable for modeling isothermal fatigue in amorphous polymers. The theory is formulated in a rate form within continuum mechanics framework without the need to measure damage changes per loading cycles. Using the approach, contribution of ratcheting to fatigue of polycarbonate (PC) was investigated and the results were compared to previous experimental observations. When subjected to uniaxial stress-controlled cyclic loadings, ratcheting deformation apparently occurs and increases with mean stress and amplitude. The development of ratcheting deformation shows an initial growth followed by a decrease to almost a constant growth rate which occupies majority of the total lifetime. Ratcheting behavior under multiaxial stress states was also investigated based on finite element analyses of a dogbone-shaped test specimen. The results show that fatigue damage develops at the sites following closely the localized plastic deformation and increases with ratcheting deformation during cyclic loadings. The results indicate that the ratcheting behavior can be exploited in the evaluation of the entire fatigue lifetime. [ABSTRACT FROM AUTHOR]