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Power electronic conversion systems introduce different types of voltage stresses on high-voltage epoxy cast insulation in medium-frequency transformers (MFTs), which challenges the reliability of MFTs. The endurance of epoxy insulation at different voltages (AC, DC and pulse) and environmental (thermal and humidity) stresses was studied using encapsulated electrodes in the absence of partial discharge. To assess aging processes and select aging state indicators, various tests including AC breakdown strength (BDE), broadband dielectric spectroscopy, small-angle x-ray scattering (SAXS), Fourier-transform infrared spectroscopy and differential scanning calorimetry (DSC) were first conducted on aged flat samples. The increase of mesoscopic free volume from the SAXS result and local densification (physical aging) of epoxy network from the DSC result were both found. BDE is proved to be sensitive to various aging conditions and thus determined as a test method for encapsulated samples. It is found that the physical aging effect under thermal stress at early aging stages can cause a reversible increase in BDE compared to non-aged samples. This effect can be erased by coupled medium-low electrical stress during aging. In contrast, a sufficiently high electric field will deepen the physical aging extent. Occasional sample failures were observed simultaneously within this process. According to the SAXS and DSC results on flat samples, the failure of encapsulated samples is possibly attributed to the chain fracture around increased mesoscopic free volume during electron bombardment and microcracks generated by interfacial stress release during physical aging. At longer aging periods, the volumetric absorption and diffusion of chemical reactants (oxygen and water) in epoxy networks at high temperatures determines the eventual decrease in BDE, which can be accelerated by the electric field. Ages with different voltage types were gauged by the reduction of BDE compared to pure environmental stress. Bipolar pulses bring heavier aging effects than ACs at the same RMS value. However, the DC component has opposite effects on the BDE with and without thermal stress. [ABSTRACT FROM AUTHOR]

Artworks, particularly easel paintings, are multi‐component materials intended to last indefinitely. The protective coatings applied to these artworks often consist of amorphous glass‐like polymers, which undergo slow physical aging and structural recovery below their glass transition temperature. This process alters key physical properties such as mechanical strength, optical clarity, and thermal stability over extended periods. This study investigates the time‐dependent evolution of these properties in Laropal A81, a widely used synthetic resin for cultural heritage conservation, particularly as a replacement for ancient varnishes. The investigation involves characterization of enthalpy recovery via differential scanning calorimetry, refractive index evolution via refractometry, and creep compliance evolution via rheological measurements. The aging behavior of Laropal A81 is further analyzed using the Kohlrausch–Williams–Watts function and the Tool–Narayanaswamy–Moynihan model, enabling the quantification of critical dynamic parameters such as activation energy, nonlinearity, partition coefficients, and non‐exponentiality. The gained insights into the long‐term behavior of this coating's properties can be valuable for improving preservation and restoration strategies for cultural heritage. [ABSTRACT FROM AUTHOR]

AbstractOur research described in this article examined the physical aging of natural rubber (NR) and nitrile rubber (NBR) compounds reinforced with nano-silica (n-SiO2) particles. The impact of NR and nano-silica content on the mechanical, spectral, and thermal properties of the composites was assessed using Shore hardness, thermal gravimetric analysis (TGA), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). The results showed that after 8 days of aging in toluene or xylene at room temperature, high NR content caused significant swelling in the non-polar solvents, unlike NBR, which prevented rubber chain stretching and reduced the free volume. The transport mechanism of the toluene and xylene was pseudo-Fickian and slightly dependent on the nano-silica content. The hardness of the vulcanized blends increased with NBR and silica incorporation due to better dispersion of the particules and rubber-filler interaction, leading to high cross-linking density. XRD patterns confirmed the filler intercalation within the polymer matrix, causing a diffraction shift to a lower 2θ value of the various reflectures. Differential thermogravimetric analysis (DTGA) revealed that the n-SiO2 nanoparticles enhanced the thermal stability due to strong polymer chain interactions. These findings suggest that nano-silica-filled NR/NBR blends have significantly improved physical, mechanical, and thermal properties, supporting their potential for advanced elastomer-based materials in industrial applications. [ABSTRACT FROM AUTHOR]

Physical aging as a novel maturation method for fruit wine is gradually gaining attention and utilization from various research institutions and enterprises. This paper aims to grasp the current research progress and future development trends of physical aging in fruit wine. Using bibliometrics, this study conducted statistical analysis on relevant studies from the China National Knowledge Infrastructure (CNKI) and Web of Science (WOS) core collections. This study also utilized the SooPAT patent search engine and the commercial query platform Tianyancha to summarize the industry's current development status. Results indicate that the total publication volume on the physical aging of fruit wine is on the rise, with Spain actively engaging in international cooperation and producing the most outcomes. Literature related to this topic in China is primarily funded by national funds and is mostly published in China Brewing journals. Through keyword analysis, current research focuses on exploring the application of physical aging technology in grape wine, examining the impact of physical aging on phenolic substances in fruit wine and investigating the influence of physical aging technology on sensory quality. In terms of industry development, relevant enterprises in China are densely distributed in coastal areas, accumulating a total of 93 patents in this field. The physical aging technology for fruit wine offers advantages such as low cost and quick effectiveness, indicating significant development potential and prospects. [ABSTRACT FROM AUTHOR]

The ability of vitrification when crossing the glass transition temperature (Tg) of confined and bulk water is crucial for myriad phenomena in diverse fields, ranging from the cryopreservation of organs and food to the development of cryoenzymatic reactions, frost damage to buildings, and atmospheric water. However, determining water's Tg remains a major challenge. Here, we elucidate the glass transition of water by analyzing the calorimetric behavior of nano-confined water across various pore topologies (diameters: 0.3 to 2.5 nm). Our approach involves subjecting confined water to annealing protocols to identify the temperature and time evolution of nonequilibrium glass kinetics. Furthermore, we complement this calorimetric approach with the dynamics of confined water, as seen by broadband dielectric spectroscopy and linear calorimetric measurements, including the fast scanning technique. This study demonstrated that confined water undergoes a glass transition in the temperature range of 170 to 200 K, depending on the confinement size and the interaction with the confinement walls. Moreover, we also show that the thermal event observed at ~136 K must be interpreted as an annealing prepeak, also referred to as the "shadow glass transition." Calorimetric measurements also allow the detection of a specific heat step above 200 K, which is insensitive to annealing and, thereby, interpreted as a true thermodynamic transition. Finally, by connecting our results to bulk water behavior, we offer a comprehensive understanding of confined water vitrification with potential implications for numerous applications. [ABSTRACT FROM AUTHOR]

This study investigated the physical aging behavior of commodity polymers, specifically polystyrene (PS) and poly(methyl methacrylate) (PMMA), across various molecular weights (MWs). Using ellipsometry, we examine the physical aging behavior of bulk polymer films supported on silicon across a wide range of quench depths below glass transition temperature. At shallow quench depths, where the physical aging behavior is thermodynamically controlled, we observe that the physical aging rate for both PS and PMMA increases with decreasing MW. The MW dependence of the physical aging rate in the thermodynamic‐control region is hypothesized to originate from the MW dependence of the fractional free volume. In support of this hypothesis, we observe that the difference in thermal expansivity between the rubbery state and the glassy state (αrubbery − αglassy), which has been demonstrated to be positively related to fractional free volume, exhibits a similar MW dependence as the physical aging behavior. This correlation lends support to the free volume model of physical aging. Building on the free volume model, we propose a method to tune the physical aging behavior, demonstrating that incorporating flexible chain ends alters the physical aging behavior in a manner akin to reducing MW. Highlights: Polystyrene and poly(methyl methacrylate) have maximum physical aging rates at specific quench depths.Physical aging behavior is thermodynamically or kinetically controlled.With thermodynamic control, the aging rate increases with a reduction in molecular weight.With thermodynamic control, the aging rate correlates with free volume.Aging behavior can be tuned by blending with low MW polymer with highly flexible chain ends. [ABSTRACT FROM AUTHOR]

Glassy polymers stiffen or soften when exposed to volatile compounds, depending on the specific combination of polymer compound and the specimen history. Relevant to the long‐term applicability of the separation membranes, three common membrane glassy polymers are studied in this work. Freshly prepared and 2‐years aged films from cellulose triacetate (CTA), poly[1‐(trimethylsilyl)‐1‐propyne] (PTMSP), and the archetypal polymer of intrinsic microporosity (PIM‐1) were tested using isothermal Dynamic Mechanical Analysis (DMA) at varied vapor activity. Vapors of organic compounds, in which the polymers do and do not dissolve in the liquid phase (solvents and nonsolvents), were studied at 40 °C, namely: dichloromethane (DCM, solvent), p‐xylene (solvent for PTMSP and PIM‐1), and methanol (nonsolvent). Functional groups of the mer units sensitive to the dissolution were identified using Raman spectroscopy. All aged films were stiffer than the freshly prepared ones. Stiffening prevailed for most freshly prepared film‐vapor pairs at low vapor saturations (activity < ≈0.4), except CTA and PIM‐1 in nonsolvent methanol vapors. Softening prevailed for the aged films and higher vapor saturations (activity > ≈0.6). Vapors of the solvents and nonsolvents did not show the expectable prevalence of softening and stiffening, respectively. Physical aging influenced the stiffening and softening of polymer glasses expectably. [ABSTRACT FROM AUTHOR]

Physical aging is an inherent property of glassy matter, but understanding its microscopic mechanism remains a challenge particularly at the particle level. In this work, we use a confocal microscope to in-situ trace the particle trajectories in a 3D colloidal glass for 73000 s, aiming at resolving the aging dynamics. By calculating the mean square displacement of particle motions, we find that the glass aging with time can be divided into three stages: β relaxation, α relaxation and free diffusion. The system's mean square displacement at each aging state is quantitatively resolved into three contributions of particle dynamics modes: vibration within the nearest-neighbor cages, hopping between cages and cooperative rearrangement. We further calculate the particle's free volume and find that the β-to-α transition is accompanied by the temporary increase of the system-averaged free volume due to pronounced hops of particles. Nevertheless, the temporal autocorrelation of the free volume spatial distribution still obeys a monotonically stretched exponential decay with an exponent of 0.76, which is related to the sub-diffusion dynamics of cooperative rearrangements and hops mixed in α relaxation. According to the resolved vibrational displacements, we calculate the vibrational density of states of this 3D glass, and the characteristic boson peak is reproduced at low frequencies. Our findings shed insight into the particle-level aging dynamics of a real glass under purely thermal activation. [ABSTRACT FROM AUTHOR]

The tensile creep tests for two kinds of epoxy resin matrix composite laminates were performed under 25°C and 50°C. Results indicate that these materials deform in a time‐dependent manner, that is, the tensile strain increases within a short time after the tests began, and then decreases during most of the loading period. Such increase and decrease trends reflect the creep characteristic and effect of physical aging, respectively. A linear viscoelastic model is developed to include both the creep temperature effect and physical aging effect, starting from the Boltzmann superposition principle. In modeling, these two effects both contribute to the transient compliance and result in the increase and decrease of the transient compliance. Time–temperature/aging time superposition principle is adopted to deal with the influences of temperature and physical aging. This theoretical model is further implemented numerically within a finite element framework. To verify the newly proposed model, not only the experimental and numerical results of the tensile deformations of laminates are compared, but also the bending deformations of structural components made from the above laminates are analyzed. Highlights: Tensile creep tests were done for carbon fiber/epoxy laminates.The strain shows creep temperature and aging effect (TE and AE).New constitutive relation was proposed to describe the TE‐ and AE‐caused strains.Structural‐level flexure creep tests and simulation analyses were conducted. [ABSTRACT FROM AUTHOR]

The direct action of salt on asphalt materials has received limited research despite the abundance of studies on salt erosion and its effects on the moisture stability of asphalt concrete. This study aimed to investigate the effects of chloride salt on the rheology of asphalt and erosion mechanisms. Microscopic properties of asphalt mortar were analyzed through scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FTIR), and the erosion degree of salt in asphalt mortar was evaluated based on three major indexes. Rheological properties of asphalt mortar were determined through temperature sweep and multiple stress creep and recovery (MSCR) tests, while the modified water-boiling test was conducted to evaluate the adhesion of asphalt mortar. Results showed that as salinity increases, the agglomerate phenomenon tends to occur in asphalt mortar, leading to physical aging effects on its basic properties. Meanwhile, chloride salt modified asphalt concrete is prone to cracking at low temperatures and has reduced durability at high temperatures, making it unsuitable for standard load or heavy traffic pavement requirements of PG64 modified asphalt. Furthermore, the presence of chloride in asphalt mortar was not conducive to its adhesion. [ABSTRACT FROM AUTHOR]

Shape memory polymers (SMPs) maintain a temporary shape after pre‐straining, wherein the polymer chains are constrained in a non‐equilibrium thermodynamic state. Physical aging lowers the chain conformational energy, which affects the mechanical properties. Herein, we investigate the relationship between physical aging and the shape recovery of SMP sheets, whereas both processes involve motion of polymer chains. We induce conformational changes to polymer chains either by physical aging or via a thermomechanical pre‐straining process. We then quantify structural relaxation via recovered enthalpy measurements using modulated differential scanning calorimetry (MDSC), and the shape recovery performance using dynamic mechanical analysis (DMA). We vary pre‐straining holding time, amount, and rate and observe the relationship between physical aging, recovered enthalpy, and the shape recovery performance. The results indicate that an increase in recovered enthalpy correlates with an increase in characteristic shape recovery time. Further, a maximum decrease in recovery time of 65% is observed at the highest strain rate, and only small amounts of recovered enthalpy occur for aging times longer than 16 h. The results provide insight into the relationship between physical aging and its effects on shape memory, which is important for applications requiring storage for long durations. [ABSTRACT FROM AUTHOR]

In this work, epoxy networks used for civil engineering constructions are aged at ambient temperature, and the impact of the early stages of aging on mechanical properties is analyzed. It is observed that Young's modulus and the yield stress increase with the aging time whereas the strain at break and the toughness decrease. The structural causes for these variations are investigated by swelling experiments, infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis. By combining experimental results, it is deduced that the aging process occurs in two stages. During the first 7 days of aging, the change in mechanical properties should essentially be attributed to the postcuring, which results in additional crosslinking reactions. When increasing the aging time to 21 days, the crosslinking density reaches a plateau, but a second stage emerges, in which the mechanical properties continue evolving in the same way, with variations of the mechanical parameters being of comparable amplitude. This second stage is attributed to the evolution of the thermodynamic state of the glass, leading to a densification of the epoxy network through minimization of the free volume, and favoring the creation of physical interactions between polymer segments. Therefore, structural relaxation is shown to have a significant impact on the mechanical properties. [ABSTRACT FROM AUTHOR]

Temperature and physical aging effects on the three-dimensional behaviors, such as shear and bulk properties, of viscoelastic solids are critical for developing polymer composite systems but are rarely addressed. Furthermore, accurate identification of time-temperature-dependent viscoelastic constitutive theories remains a challenging problem. In this work, we propose a robust and automated method to simultaneously identify the viscoelastic, temperature, and physical aging related three-dimensional model parameters based on the Bayesian framework. The proposed method was applied to three-dimensional experimental data from nonisothermal physical aging tests on polycarbonate at different temperatures. The posterior distribution of the model parameters was obtained through Markov chain Monte Carlo (MCMC) simulations, which allowed us to determine the minimum number of material parameters yielding an optimized accuracy. The experimental results are in excellent agreement with the predictions of the identified parameters. Moreover, we have found through the experimental results that the shear properties of polycarbonate are affected by temperature and physical aging, whereas its bulk properties are affected only by temperature and are relatively insignificant in comparison to the shear properties. The proposed method can be applied to polymers or composites to predict their long-term three-dimensional mechanical properties under complex working conditions. [ABSTRACT FROM AUTHOR]

Aggregation‐induced emission (AIE) luminogens are attractive dyes to probe polymer properties that depend on changes in chain mobility and free volume. When embedded in polymers the restriction of intramolecular motion (RIM) can lead to their photoluminescence quantum yield (PLQY) strong enhancement if local microviscosity increases (lowering of chain mobility and free volume). Nonetheless, measuring PLQY during stimuli, i.e. heat or mechanical stress, is technically challenging; thus, emission intensity is commonly used instead, assuming its direct correlation with the PLQY. Here, by using fluorescence lifetime as an absolute fluorescence parameter, it is demonstrated that this assumption can be invalid in many commonly encountered conditions. To this aim, different polymers are loaded with tetraphenylenethylene (TPE) and characterized during the application of thermal and mechanical stress and physical aging. Under these conditions, polymer matrix transparency variation is observed, possibly due to local changes in refractive index and to the formation of microfractures. By combining different characterization techniques, it is proved that scattering can affect the apparent emission intensity, while lifetime measurements can be used to ascertain whether the observed phenomenon is due to modifications of the photophysical properties of AIE dyes (RIM effect) or to alterations in the matrix optical properties. [ABSTRACT FROM AUTHOR]

Abstract Aggregation‐induced emission (AIE) luminogens are attractive dyes to probe polymer properties that depend on changes in chain mobility and free volume. When embedded in polymers the restriction of intramolecular motion (RIM) can lead to their photoluminescence quantum yield (PLQY) strong enhancement if local microviscosity increases (lowering of chain mobility and free volume). Nonetheless, measuring PLQY during stimuli, i.e. heat or mechanical stress, is technically challenging; thus, emission intensity is commonly used instead, assuming its direct correlation with the PLQY. Here, by using fluorescence lifetime as an absolute fluorescence parameter, it is demonstrated that this assumption can be invalid in many commonly encountered conditions. To this aim, different polymers are loaded with tetraphenylenethylene (TPE) and characterized during the application of thermal and mechanical stress and physical aging. Under these conditions, polymer matrix transparency variation is observed, possibly due to local changes in refractive index and to the formation of microfractures. By combining different characterization techniques, it is proved that scattering can affect the apparent emission intensity, while lifetime measurements can be used to ascertain whether the observed phenomenon is due to modifications of the photophysical properties of AIE dyes (RIM effect) or to alterations in the matrix optical properties.

Metallic glass formers are a relatively new entry in glass physics, which has attracted large interest in both physics and materials science communities due to the unique mechanical and structural properties of these materials. Physical aging is however one of the main obstacle to their widespread use as it affects their properties at all length scales. The knowledge of the microscopic mechanisms inducing aging and relaxation is therefore extremely important for both fundamental and applied sciences. In this article we present a review of the recent advances made with the X-ray photon correlation spectroscopy technique on the study of the collective particle motion and physical aging in metallic glasses at the atomic level. We show that a careful tuning of the sample preparation or the application of specific thermal protocols have the potential to drive the glass into more aged or rejuvenated microscopic configurations with different stabilities.

Copyright of China Pulp & Paper is the property of China Pulp & Paper Magazines Publisher and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

We follow the assumption that the dilatational response of glassy polymers can be characterized by a back-stress type analog that includes a thermal expansion for each elastic component and with a viscosity that is dependent on the expansion of the elastic back-stress component. To this, we add the assumption of an unloaded equilibrium temperature that correlates to the past processing through the viscous flow. After setting this in a thermodynamically consistent structure, elastic, elastic back-stress, thermal expansion, back-stress thermal expansion, heat capacity, and viscous damping are evaluated using existing experiments for the response of polycarbonate over the glassy and rubbery ranges. For the demonstration, this is done entirely using a WLF shift factor that is augmented to include, in addition, back strain superposition. We then examine the resulting model under different thermal and mechanical loadings that have the material passing through the glass transition. [ABSTRACT FROM AUTHOR]

Filler reinforced rubber is widely used for engineering applications; therefore, a sound characterization of the effects of physical aging is crucial for accurately predicting its viscoelastic properties within its operational temperature range. Here, the torsion pendulum is used to monitor the evolution of the storage and loss modulus of carbon black filled samples for four days after a temperature drop to 30   ° C . The storage modulus presents a continuous increase, while the loss modulus generally displays a steady decrease throughout the four days that each test was conducted. The relationship of the recovery rates with the carbon black properties is also studied, analysing its dependency on the particle size and aggregate structure. The evolution of the recovery rate seems to depend linearly on the surface area while the carbon black structure appears to have a much weaker influence on the physical aging behavior for the set of compounds tested. The obtained results corroborate the presence of physical aging at room temperature for filler rubber materials and the ability of the torsion pendulum to monitor the storage and loss modulus change, providing pivotal data on the influence of physical aging on the viscoelastic properties of the material. [ABSTRACT FROM AUTHOR]

Abstract Background To explore whether differences between men and women in the sensitivity to (strength of the association) and/or in the exposure to determinants (prevalence) contribute to the difference in physical functioning, with women reporting more limitations. Methods Data of the Doetinchem Cohort Study was used (n = 5856, initial ages 26–70 years), with follow-up measurements every 5 years (up to 20). Physical functioning (subscale SF-36, range:0–100), sex (men or women) and a number of socio-demographic, lifestyle- and health-related determinants were assessed. Mixed-model multivariable analysis was used to investigate differences between men and women in sensitivity (interaction term with sex) and in exposure (change of the sex difference when adjusting) to determinants of physical functioning. Results The physical functioning score among women was 6.55 (95%CI:5.48,7.61) points lower than among men. In general, men and women had similar determinants, but pain was more strongly associated with physical functioning (higher sensitivity), and also more prevalent among women (higher exposure). The higher exposure to low educational level and not having a paid job also contributed to the lower physical functioning score among women. In contrast, current smoking, mental health problems and a low educational level were more strongly associated with a lower physical functioning score among men and lower physical activity and higher BMI were more prevalent among men. Conclusions Although important for physical functioning among both men and women, our findings provide no indications for reducing the difference in physical functioning by promoting a healthy lifestyle but stress the importance of differences in pain, work and education.

Physical aging deals with slow property changes over time caused by molecular rearrangements. This is relevant for non-crystalline materials such as polymers and inorganic glasses, both in production and during subsequent use. The Narayanaswamy theory from 1971 describes physical aging—an inherently nonlinear phenomenon—in terms of a linear convolution integral over the so-called material time ξ. The resulting “Tool–Narayanaswamy (TN) formalism” is generally recognized to provide an excellent description of physical aging for small, but still highly nonlinear, temperature variations. The simplest version of the TN formalism is single-parameter aging according to which the clock rate dξ/dt is an exponential function of the property monitored. For temperature jumps starting from thermal equilibrium, this leads to a first-order differential equation for property monitored, involving a system-specific function. The present paper shows analytically that the solution to this equation to first order in the temperature variation has a universal expression in terms of the zeroth-order solution, R0(t). Numerical data for a binary Lennard–Jones glass former probing the potential energy confirm that, in the weakly nonlinear limit, the theory predicts aging correctly from R0(t) (which by the fluctuation–dissipation theorem is the normalized equilibrium potential-energy time-autocorrelation function).

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

This paper provides a viewpoint of the technology of the fast-scanning calorimetry with the relaxation behavior of disordered side chains of poly[2,5-bis(3-dodecylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTT-C12) around the glass transition temperature of the side chains (Tg,γ). PBTTT is an ideal model of the high-performance copolymer of poly(alkylthiophenes) with side chains. The γ1 relaxation process of the disordered side chains of PBTTT was detected as a small endothermic peak that emerges before the γ2 relaxation process. It shows an increase with increasing temperature as it approaches the glass transition temperature of the disordered side chains of PBTTT. The ductile–brittle transition of PBTTT in low temperatures originating from the thermal relaxation process is probed and illustrated by physical aging experiments. The signature is shown that the relaxation process of the disordered side chain of PBTTT at low temperatures varies from Arrhenius temperature dependence to super Arrhenius temperature dependence at high temperatures. These observations could have significant consequences for the stability of devices based on conjugated polymers, especially those utilized for stretchable or flexible applications, or those demanding mechanical robustness during tensile fabrication or use in a low-temperature environment. [ABSTRACT FROM AUTHOR]

Poly(lactic acid) (PLA) is a promising bio-based environmentally-friendly plastic. Nevertheless, the physical aging-induced brittleness of PLA limits its widespread applications. Blending with immiscible ductile polymer is an effective way to toughen PLA. However, the underlying details of the toughening mechanism and, in particular, the effect of physical aging are not well understood. Herein, atomic force microscopy (AFM) based nanomechanical mapping technology was utilized to visualize the differences in the deformation mechanisms between unaged and aged PLA/poly(ε-caprolactone) (PCL) blend upon uniaxial drawing. Results show that physical aging has a significant effect on the microscopic Young's modulus and its distribution of PLA matrix, resulting in a highly heterogeneous response of the PLA/PCL blend to external stress and affecting the mechanical properties of the PLA phase under different extensions. This work provides a new experimental basis for understanding the effect of physical aging on the mechanical properties of PLA-based materials. [ABSTRACT FROM AUTHOR]

In this study, the effect of moisture on the elastic and failure properties of elastomeric polyurethane (EPU 40) 3D printed via Vat Photopolymerization was investigated. EPU 40 samples were printed, and uniaxial tensile tests were performed on Dry-fresh, Dry-aged (eight months aged), and after various times of being immersed in water (0–8 months). Elastic response, initial stiffness, failure strength, and failure elongation were analyzed. Besides, gravimetric analysis was performed to determine the increase in weight and thickness after water immersion. The elastic response was fitted by the Arruda-Boyce constitutive model. Results show that initial stiffness decreased after immersion (mean 6.8 MPa dry vs. 6.3 MPa immersed p-value 0.002). Contrary, the initial stiffness increased due to physical aging under a dry state from a mean 6.3 MPa to 6.9 MPa (p = 0.006). The same effect was observed for stiffness parameter G of the constitutive model, while the limit stretch parameter λ L was not affected by either aging. The 95% confidence intervals for strength and failure stretch were 5.27–9.48 MPa and 2.18–2.86, respectively, and were not affected either by immersion time or by physical aging. The median diffusion coefficient was 3.8 · 10 − 12   m ^ 2 / s . The immersion time has a significant effect only on stiffness, while oxidative aging has an inverse effect on the mechanical properties compared to water immersion. The transition process is completed within 24 h after immersion. [ABSTRACT FROM AUTHOR]

Optimizing the pigment volume concentration of zinc phosphate pigments can protect Al alloy 6101 from alkaline media. Additionally, zinc phosphate pigments form a shielding film on the substrate and facilitate stopping the penetration of aggressive corrosion ions. The efficiency of eco-friendly zinc phosphate pigments is almost 98% during the corrosion analysis. A comparative study of physical aging of neat epoxy and Zinc Phosphate (ZP) pigment-modified epoxy coatings on Al alloy 6101 was conducted in Xi’an, China, for one year in all four seasons, where in summer for 3 months, results degraded more due to high UV radiation and humidity; it is found that peeling force of ZP pigments modified epoxy coatings is 50% higher of than that of the neat epoxy coatings though both peel-off adhesion strength and scratch test visibility decreased in both coatings; The electrochemical resistance of ZP pigments modified epoxy coatings is about 30% higher of than that of neat epoxy coatings, the corrosion rate of ZP pigments modified epoxy coatings is about 70% lower of than that of neat epoxy coatings, moreover the gloss retention is 20% higher in the modified epoxy; Optical surface observation of the coatings showed that the ZP modified epoxy coating could effectively restrict the crack and shrinkage in coatings after aging experimentation in the natural environment.

Carbon molecular sieve (CMS) membranes offer the best available combination of scalable economical processability with excellent separation performance. Physical aging of CMS membranes causes pore structure changes over time that affect CMS membrane performance. To provide fundamental insights into the structure evolution in CMS membranes during physical aging, a combined dual‐mode sorption and transport model is used in this study to characterize the diffusion coefficients of gas molecules in fresh and 7‐day vacuum aged CMS membranes. The results show physical aging of CMS membrane is primarily "diffusion related" and such aging behavior simultaneously causes ultramicropore changes in the continuous phase and Langmuir phase of CMS membrane. The new insights offered in this study suggest strategies to control the physical aging of CMS membranes and even use it as a valuable tool to tune the separation performance of CMS membranes for demanding gas separations. [ABSTRACT FROM AUTHOR]

Background: Characterizing the mechanical behavior of materials at elevated temperatures is critical for the design and development of polymer systems for use in complex operating conditions. The commonly used Dynamic Mechanical Analysis (DMA) does not apply to the investigation of the three-dimensional properties of materials. A combination of a mechanical testing system and an environmental chamber with extensometer measurements is more suitable for this purpose. However, the bi-axial extensometer suffers errors in measuring strains in thermoplastic specimens at elevated temperatures due to its characteristics. Objective: This brief technical note analyzes the source of measurement errors with an extensometer and proposes a robust and straightforward experimental procedure for three-dimensional mechanical testing at high temperatures. Methods: Two temperature and physical aging effects characterization experiments on polycarbonate at 120 ∘ C were performed as a case study. Thermal and penetration drifts were analyzed and corrected in the axial and transverse measurements. Results: The corrected experimental results for the two tests are nearly identical, attesting to the reproducibility of the proposed procedure. Furthermore, the bulk-related strain computed using the corrected strain increases monotonically with time, consistent with the thermodynamic principle, thus demonstrating the reliability of experimental results. Conclusions: The methodology described in this work can serve as a protocol to guide the three-dimensional thermo-mechanical testing with a bi-axial extensometer. [ABSTRACT FROM AUTHOR]

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The effects of annealing conditions and molecular weight on the energies required for cracking and plastic deformation were investigated by the essential work of fracture (EWF) method. We found that the energy required for plastic deformation, βwp, regardless of the molecular weight, decreased upon annealing, and the energy required for cracking, we, did not change. On the basis of these results, it is suggested that annealing affects βwp because the density fluctuation is amplified by annealing, and as a result, the strain in the plastic region is concentrated. Moreover, both βwp and we increased with the molecular weight because the increase of molecular weight increases the number of entanglements formed by a molecular chain. In addition, comparing the values of the J‐integral (Jc), we found that we obtained from the EWF and Jc was almost the same, indicating that we obtained from the EWF also involves the energy required for plastic deformation when the deformation around the notch changes from biaxial stretching to uniaxial stretching. [ABSTRACT FROM AUTHOR]

The effect of physical aging of the partially miscible blend of polycarbonate:polystyrene (PC:PS) at temperatures near the glass transition temperature (Tg) of the PS was studied as a function of time. For this purpose, blends of PC and PS with different ratios were elaborated and characterized using SEM, FTIR, DSC, and DMA techniques. The results indicated the presence of weak interaction upon blending with a maximum of interaction for the 50:50 blend. The effect of physical aging on the latter was then investigated via DMA, DSC, and NMR analyses. The DMA results showed that both phases were sensitive to aging. The effect was found to be strongly dependent on both the temperature and time. The aging of PC:PS blend was also found to trap stress during the process which induced an instability in the viscoelastic behavior. The latter was found to be associated with a phase‐separation morphology of the blend and influenced by its composition. The NMR analysis also showed a pronounced distortion of the conformation combined with increasing molecular motion. These effects were found to be important for aging below the PS's Tg. [ABSTRACT FROM AUTHOR]

Residual strains and shape distortions in a polymer-based composite structure may depend on the cure schedule used for manufacture. Aiming to understand the cure history effects, the influence of the curing "path" (time t c and temperature T c path during curing) on viscoelastic (VE) response of a fully cured (FC) (α = 0.992) epoxy was investigated. Five different "families" of the same epoxy were manufactured in constraint-free conditions using different sets of curing parameters. Then, tensile tests were performed at different temperatures (T = 30 to 110 °C), and the time–temperature superposition principle (TTSP) and Schapery's type of linear viscoelastic (VE) model, accounting for physical aging of specimens tested at high temperature, were used. The results show that the VE properties of the studied epoxy are independent of the curing history provided that at the end all specimens are fully cured. Also, the physical aging rate at high temperatures of all "families" is the same and it can be described by a simple aging-temperature independent equation reported in Nunes et al.1 It is expected that curing history of unconstrained and fully cured epoxy has an insignificant effect on final viscoelastic behavior, a knowledge which could assist in developing more time and cost-efficient cure cycles. [ABSTRACT FROM AUTHOR]

Physical aging deals with slow property changes over time caused by molecular rearrangements. This is relevant for non-crystalline materials such as polymers and inorganic glasses, both in production and during subsequent use. The Narayanaswamy theory from 1971 describes physical aging—an inherently nonlinear phenomenon—in terms of a linear convolution integral over the so-called material time ξ. The resulting "Tool–Narayanaswamy (TN) formalism" is generally recognized to provide an excellent description of physical aging for small, but still highly nonlinear, temperature variations. The simplest version of the TN formalism is single-parameter aging according to which the clock rate d ξ / d t is an exponential function of the property monitored. For temperature jumps starting from thermal equilibrium, this leads to a first-order differential equation for property monitored, involving a system-specific function. The present paper shows analytically that the solution to this equation to first order in the temperature variation has a universal expression in terms of the zeroth-order solution, R 0 (t) . Numerical data for a binary Lennard–Jones glass former probing the potential energy confirm that, in the weakly nonlinear limit, the theory predicts aging correctly from R 0 (t) (which by the fluctuation–dissipation theorem is the normalized equilibrium potential-energy time-autocorrelation function). [ABSTRACT FROM AUTHOR]

Abstract Background This study explores whether a sex difference in sensitivity to (strength of the association) and/or in exposure to (prevalence) determinants of gait speed contributes to the observed lower gait speed among older women compared to men. Methods Data from the Longitudinal Aging Study Amsterdam (LASA) were used. In total 2407 men and women aged 55–81 years were included, with baseline measurements in 1992/2002 and follow-up measurements every 3–4 years for 15/25 years. Multivariable mixed model analysis was used to investigate sex differences in sensitivity (interaction term with sex) and in exposure to (change of the sex difference when adjusted) socio-demographic, lifestyle, social and health determinants of gait speed. Results Women had a 0.054 m/s (95 % CI: 0.076 − 0.033, adjusted for height and age) lower mean gait speed compared to men. In general, men and women had similar determinants of gait speed. However, higher BMI and lower physical activity were more strongly associated with lower gait speed in women compared to men (i.e. higher sensitivity). More often having a lower educational level, living alone and having more chronic diseases, pain and depressive symptoms among women compared to men also contributed to observed lower gait speed in women (i.e. higher exposure). In contrast, men more often being a smoker, having a lower physical activity and a smaller personal network size compared to women contributed to a lower gait speed among men (i.e. higher exposure). Conclusions Both a higher sensitivity and higher exposure to determinants of gait speed among women compared to men contributes to the observed lower gait speed among older women. The identified (modifiable) contributing factors should be taken into account when developing prevention and/or treatment strategies aimed to enhance healthy physical aging. This might require a sex-specific approach in both research and clinical practice, which is currently often lacking.

In this work we study the molecular mobility in the amorphous solid state and in the glass transformation region of two compounds, diazepam and nordazepam; these are two benzodiazepines, a family of psychotropic drugs with sedative, anxiolytic and muscle-relaxing properties. The experimental techniques used are thermostimulated currents (TSC) and differential scanning calorimetry (DSC). TSC is a time-dependent technique recognized for its high resolving power; the use of this technique in the depolarization and polarization modes (TSDC and TSPC respectively), provides results that confirm and complement results of dielectric relaxation spectroscopy (DRS) published recently. On the other hand, the variation with the heating rate of the temperature position of the DSC glass transition signal also allowed the estimation of the activation energy at T g and of the dynamic fragility of the two glass formers. [ABSTRACT FROM AUTHOR]

Recent efforts, fostered by a pioneering work by us, have shown the of multiple steps in the recovery of equilibrium of glasses. Jin and McKenna raise concerns regarding the validity of such scenario alleging that the multiple recovery steps would be an artifact arising from poor temperature control in the oven used for isothermal glass equilibration. We critically discuss Jin and McKenna arguments from both the viewpoints of scrutinizing previous literature data and that of the temperature control in the oven. In doing so, we provide compelling arguments that Jin and McKenna conjectures are unjustified and point out the need for efforts to describe glass dynamics significantly below the glass transition temperature, Tg, by accounting for the presence of different relaxation mechanisms active in glass equilibration. [ABSTRACT FROM AUTHOR]

Background: To explore whether differences between men and women in the sensitivity to (strength of the association) and/or in the exposure to determinants (prevalence) contribute to the difference in physical functioning, with women reporting more limitations. Methods: Data of the Doetinchem Cohort Study was used (n = 5856, initial ages 26–70 years), with follow-up measurements every 5 years (up to 20). Physical functioning (subscale SF-36, range:0–100), sex (men or women) and a number of socio-demographic, lifestyle- and health-related determinants were assessed. Mixed-model multivariable analysis was used to investigate differences between men and women in sensitivity (interaction term with sex) and in exposure (change of the sex difference when adjusting) to determinants of physical functioning. Results: The physical functioning score among women was 6.55 (95%CI:5.48,7.61) points lower than among men. In general, men and women had similar determinants, but pain was more strongly associated with physical functioning (higher sensitivity), and also more prevalent among women (higher exposure). The higher exposure to low educational level and not having a paid job also contributed to the lower physical functioning score among women. In contrast, current smoking, mental health problems and a low educational level were more strongly associated with a lower physical functioning score among men and lower physical activity and higher BMI were more prevalent among men. Conclusions: Although important for physical functioning among both men and women, our findings provide no indications for reducing the difference in physical functioning by promoting a healthy lifestyle but stress the importance of differences in pain, work and education. [ABSTRACT FROM AUTHOR]

We investigate the start-up dynamics under a stress-controlled flow field in aging soft materials, with the aid of an inelastic structural-kinetic model that exhibits non-monotonic steady-state shear stress–shear rate flow curve. In particular, we focus on the occurrence of both transient and steady-state shear banding in such systems. We find that even when the applied stress is greater than the minimum value of the stress associated with the non-monotonic flow curve, the system could eventually undergo structural arrest, resulting in a complete stoppage of flow. For further increase in stress, the system progressively shows transient shear banding as well as apparent steady-state shear banding. At sufficiently high shear stresses, the model shows an eventual homogeneous steady state. We delineate the effects of inertia and waiting time on the transient and apparent steady-state shear banding. [ABSTRACT FROM AUTHOR]

Epoxy systems are widely used as matrix resins for fiber reinforced polymers (FRP) and, therefore, often have to withstand harsh environmental conditions. Especially in marine and offshore environments, moisture or direct water contact leads to water absorption into the epoxy resin. As a result, the mechanical properties change during application. Since diffusion at room or colder temperatures is slow, industry and academia typically use accelerated aging methods at elevated temperatures for durability prediction. However, as the water-polymer interaction is a complex combination of plasticization, physical aging, and molecular interaction, all of these mechanisms are expected to be affected by the ambient temperature. To reveal the impact of aging time and temperature on the thermo-mechanical properties of an amine-epoxy system, this publication includes various hygrothermal aging conditions, like water bath and relative humidity aging at temperatures ranging from 8°C to 70°C and relative humidity from 20% to 90%. Thus, it is demonstrated via long-term aging, DMTA and FTIR investigations that, e.g., strength, stiffness, strain to failure, and the glass transition temperature (Tg) can differ significantly depending on aging time and temperature. For example, it can be shown that water absorption at cold temperatures leads to the strongest and longest-lasting reduction in strength, although the maximum water absorption amount is lower than at higher temperatures. For the application, this means that strength differences of up to 26% can be obtained, depending on the aging method selected. Furthermore, it can be shown that conventional prediction models, such as Eyring correlation, which consider the mobility of the molecular structure for the prediction of thermo-mechanical properties, can only be used to a limited extent for prediction in hygrothermal aging. The reasons for this are seen to be, in particular, the different characteristics of the water-polymer interactions depending on the aging temperature. While plasticization dominates in cold conditions, relaxation and strong water-molecule bonds predominate in warm conditions.

The effect of physical aging on the viscoelastic (VE) behavior of epoxy resin is investigated experimentally performing strain-controlled tests at various temperatures on specimens aged at different temperatures (TA) for different times (tA). The aging effect is analyzed using as a framework Schapery's type of thermo-aging-rheologically simple (T-A-R simple) VE model that contains aging-state and test-temperature dependent shift factor. Experiments show that in first approximation, the shift factor can be presented as the product of aging related shift factor aA and temperature related factor aT. It is found that for short aging times the change rate of the aging shift factor with tA does not depend on TA, whereas for long tA at high TA the rate increases. Shift factors alone are not able to explain differences in relaxation curves for almost “fully” aged specimens aged at different high TA, It is shown that a T-A-R complex VE model with two additional aging-dependent functions can describe the observed discrepancies.

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.

Microporous glassy polymer membranes suffer from physical aging, which adversely affects their performance in the short time frame. We show that the aging propensity of a model microporous polymer, poly(1-trimethylsilyl-1-propyne) (PTMSP), can be effectively mitigated by blending with as little as 5 wt % porous polymer network (PPN) composed of triptycene and isatin. The aging behavior of these materials was monitored via N 2 pure gas permeability measurements over the course of 3 weeks, showing a 14% decline in PTMSP blended with 5 wt % PPN vs a 41% decline in neat PTMSP. Noteworthy, PPNs are 2 orders of magnitude cheaper than the porous aromatic frameworks previously used to control PTMSP aging. A variety of experimental and computational techniques, such as Positron Annihilation Lifetime Spectroscopy (PALS), free volume measurements, cross-polarization/magic angle spinning (CP/MAS) 13 C NMR, transport measurements and molecular dynamics (MD) simulations were used to uncover the molecular mechanisms leading to enhanced aging resistance. We show that partial PTMSP chain adsorption into the PPN porosity reduces the PTMSP local segmental mobility, leading to improved aging resistance. Permeability coefficients were broken into their elementary sorption and diffusion contributions, to elucidate the mechanism by which the reduced PTMSP local segmental mobility affects selectivity in gas separation applications. Finally, we demonstrate that in these systems, where both chemical and physical interactions take place, transport coefficients must be corrected for thermodynamic nonidealities to avoid erroneous interpretation of the results.

This work presents a detailed study, by thermostimulated depolarization currents, of the molecular mobility of poly (ether imide) in a broad temperature range covering the amorphous solid state, the glass transition, and the rubber state. Taking advantage of the very wide distribution of motional modes of the PEI glass transition (the broadest of all known glass formers), we carried out an in‐depth study of physical aging involving different modes, which provided a more comprehensive view of the aging process. We also analyzed in detail the mobility below Tg where, in addition to the fast secondary relaxation, we identified a Johari–Goldstein. In the rubber state, on the other hand, we detected a mobility but showed that it corresponds to space charge motions rather to dipolar reorientations. [ABSTRACT FROM AUTHOR]

Propane (C3H8) and propylene (C3H6) are important energy resources and raw materials for industrial chemistry. Today, propylene/propane separations are carried out by expensive distillation operations which are energy intensive. Therefore, there is a great interest in the development of new separation technologies like membrane modules. In this work, we collected and analyzed the data from neat polymers and mixed matrix membranes (MMM) for propylene/propane separations. Polymeric membranes are easily processed, but one important problem is plasticization since both propylene and propane are condensable gases resulting in a loss of selectivity. To improve the properties of polymer membranes, MMM were developed based on an inorganic filler and a polymer matrix to get improved performances with a synergistic effect. However, these performances strongly depend on the filler type and content, as well as their compatibility. In this review, the separation performances of neat polymers and MMM flat membranes and hollow fibers are reported. A comparison of the single gas and mixed gas permeation is presented where both permeability and selectivity are lost due to plasticization and the competitive sorption between gas molecules. Based on the results available, it can be concluded that more development can lead to improved performances for industrial-scale applications in the petroleum industries. Also, an upper bound for C3H6/C3H8 separation is proposed using neat polymers. [ABSTRACT FROM AUTHOR]