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• The physical aging study of a 62.5GeS2-12.5Sb2S3-25CsCl glass is investigated. • A unexpected crystallization is observed during the physical aging process. • The glass has reached its equilibrium state during aging before crystallizing. The goal of this work is to provide an answer to the important scientific question: will a glass-forming liquid reach its equilibrium state or not before to crystallize during physical aging process, i.e. when it is maintained below its glass transition temperature? For this goal the physical aging process in a 62.5GeS 2 -12.5Sb 2 S 3 -25CsCl glass has been investigated for a long period (5 months) at 30°C below the glass transition temperature T g. A crystallization was observed during this process, and was characterized through X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and Temperature Modulated Differential Scanning Calorimetry (MT-DSC) analyses. By evaluating the enthalpy loss related to the physical aging and by comparing this experimental quantity to the theoretical one, we have proved that this glass has reached its thermodynamic equilibrium state before crystallizing. Thus, this work evidences experimentally the ability for a glass former to crystallize under T g after reaching its equilibrium state. [ABSTRACT FROM AUTHOR]

The loss of internal pores, a process known as physical aging, inhibits the long-term use of the most promising gas-separation polymers. Previously we reported that a porous aromatic framework (PAF-1) could form a remarkable nanocomposite with gas-separation polymers to stop aging. However, PAF-1 synthesis is very onerous both from a reagent and reaction-condition perspective, making it difficult to scale-up. We now reveal a highly dispersible and scalable additive based on α,α′-dichloro- p-xylene ( p-DCX), that inhibits aging more effectively, and crucially almost doubles gas-transport selectivity. These synergistic effects are related to the intimately mixed nanocomposite that is formed though the high dispersibility of p-DCX in the gas-separation polymer. This reduces particle-size effects and the internal free volume is almost unchanged over time. This study shows this inexpensive and scalable polymer additive delivers exceptional gas-transport performance and selectivity. [ABSTRACT FROM AUTHOR]

The bulk charge transport in a series of regioregular poly(3-hexylthiophene) materials with different molecular weights (MW) has been studied by the time-of-flight technique. Three distinct temperature regions with transitions at ∼60 and ∼140 °C in lower MW material (9.6 kDa), and four regions with an additional transition at ∼180 °C in higher MW material (32.3 kDa) are identified in the temperature dependence of charge carrier mobility and the origin of these transitions is discussed. A pronounced effect of physical aging which reveals as a reversible increase of charge mobility is found. Densification of amorphous phase in-between the nanocrystals, which reduces the potential energy barriers and provides larger charge transfer integrals, is proposed as an origin of the effect. [ABSTRACT FROM AUTHOR]

ABSTRACT Matrix free assemblies of polymer-grafted, 'hairy' nanoparticles (aHNP) exhibit novel morphology, dielectric, and mechanical properties, as well as providing means to overcome dispersion challenges ubiquitous to conventional polymer-inorganic nanocomposite blends. Physical aging of the amorphous polymer glass between the close-packed nanoparticles (NPs) will dominate long-term stability; however, the energetics of volume recovery within the aHNPs is unknown. Herein, we compare glass transition temperature ( Tg) and enthalpy recovery of aHNPs to NP-polymer blends, across different nano-silica loadings (0-50 v/v%) and canopy architecture of polystyrene (PS) grafted silica. For aHNPs, the grafting of PS to silica imposes an additional design constraint between silica volume fraction, graft density, and graft molecular weight. At low and intermediate silica volume fraction, the Tg of blended nanocomposites is independent of silica content, reflecting a neutral polymer-NP interface. For aHNPs, the Tg decreases with silica content, implying that chain tethering decreases local segment density more than the effect of molecular weight or polymer-NP interactions. Additionally, the Tg of the aHNPs is higher than a linear matrix of comparable molecular weight, implying a complementary effect to local segment density that constrains cooperativity. In contrast, enthalpy recovery rate in the blend or aHNP glass is retarded comparably. In addition, a cross-over temperature, Tx, emerges deep within the glass where the enthalpy recovery process of all nanocomposites becomes similar to linear unfilled matrices. Differences between structural recovery in aHNP and blended nanocomposites occur only at the highest silica loadings (∼ 50 v/v%), where enthalpy recovery for aHNPs is substantially suppressed relative to the blended counterparts. The absence of physical aging at these loadings is independent of brush architecture (graft density or molecular weight of tethered chains) and indicates that the impact of chain tethering on effective bulk structural relaxation starts to appear at particle-particle surface separations on the order of the Kuhn length. Overall, these observations can be understood within the context of how three separate structural characteristics impact local segment density and relaxation processes: the dimension and architecture of the tethered polymer chains, the separation between NP surfaces, and the confinement imposed by chain tethering and space filling within the aHNP. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 319-330 [ABSTRACT FROM AUTHOR]

This paper presents a study of the physical aging of asymmetric polyetherimide (PEI) flat membranes. The effects of storage type (under vacuum, atmospheric air, and pure argon), the presence of polydimethylsiloxane (PDMS) coating, membrane heat-treatment temperature, and membrane-preparation PEI wt% on the physical aging were investigated over 240 days by monitoring CO 2 permeance and CO 2 /CH 4 selectivity of the membranes. The feed was a 10/90 V/V CO 2 /CH 4 binary gas mixture. Physical aging was quantified in terms of CO 2 permeance ultimate change and aging time constant, as well as CO 2 /CH 4 selectivity ultimate change and aging time constant. New first-order physical-aging models were proposed and shown to predict the physical aging accurately. This study indicates that physical aging decreases the permeance but increases the selectivity. The membranes age less when (a) they have a PDMS coating, (b) they are prepared with a higher PEI wt%, and (c) they have a higher annealing temperature, especially above the glass transition temperature. Membranes stored under vacuum age at a slower rate than those stored under atmospheric air or pure argon. [ABSTRACT FROM AUTHOR]

Physical aging in high free volume polymers reduces gas permeability which limits their potential for gas separation. Plasticization is another concern when the separation involves a highly condensable gas such as CO 2 or operates in aggressive conditions. This work reports a straightforward strategy to suppress aging and plasticization of polymers of intrinsic microporosity, specifically PIM-1, with a tailored high CO 2 permeability, by the incorporation of POSS nanoparticles. The nanoparticles enhances gas diffusivity at low particle loadings while induces chain rigidification at high particle loadings. The newly developed membrane materials are promising for CO 2 capture and other gas separation. [ABSTRACT FROM AUTHOR]

The synthesis and gas permeation properties of two 6FDA-dianhydride-based polyimides prepared from 2,6-diaminotriptycene (6FDA–DAT1) and its extended iptycene analog (6FDA–DAT2) are reported. The additional benzene ring on the extended triptycene moiety in 6FDA–DAT2 increases the free volume over 6FDA–DAT1 and reduces the chain packing efficiency. The BET surface area based on nitrogen adsorption in 6FDA–DAT2 (450 m 2 g −1 ) is ~40% greater than that of 6FDA–DAT1 (320 m 2 g −1 ). 6FDA–DAT1 shows a CO 2 permeability of 120 Barrer and CO 2 /CH 4 selectivity of 38, whereas 6FDA–DAT2 exhibits a 75% increase in CO 2 permeability to 210 Barrer coupled with a moderate decrease in selectivity (CO 2 /CH 4 =30). Interestingly, minimal physical aging was observed over 150 days for both polymers and attributed to the high internal free volume of the shape-persistent iptycene geometries. The aged polyimides maintained CO 2 /CH 4 selectivities of 25–35 along with high CO 2 permeabilities of 90–120 Barrer up to CO 2 partial pressures of 10 bar in an aggressive 50:50 CO 2 :CH 4 mixed-gas feed, suggesting potential application in membranes for natural gas sweetening. [ABSTRACT FROM AUTHOR]

This study considers separation performance of carbon molecular sieve (CMS) membranes formed by pyrolysis under argon at 550 °C for four novel polyimide precursors referred to as 6FDA/DETDA, 6FDA:BPDA(1:1)/DETDA, 6FDA/DETDA:DABA(3:2) and 6FDA/1,5-ND:ODA(1:1). The CMS precursors were characterized using Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), and Wide-angle X-ray Diffraction (WAXD). Separation performance of polymer precursor films formed from these polymers was examined using pure gases CO 2 , CH 4 , O 2 and N 2 ; a relationship between gas permeability and polymer fractional free volume (FFV) is reported. The pyrolyzed polymer precursor films to create dense CMS membranes produced separation performance that significantly exceeded the polymer precursor performance in all cases. The 6FDA/DETDA:DABA(3:2) derived CMS membranes showed the highest permeability (above 20,000 barrer for CO 2 and above 4000 barrer for O 2 at 35 °C) and offered the greatest practical potential among the various precursors. Separation performance of the CMS membranes was studied as a function of time, with storage under vacuum between tests to assess physical aging. As expected, permeability showed a decreasing trend with time, and CO 2 /CH 4 , O 2 /N 2 selectivity showed an increasing trend. Sorption isotherms also provided insight into the microstructure evolution over time. For practical applications, continuous active feed of mixed gas 50% CO 2 /50% CH 4 was shown to effectively suppress physical aging in 6FDA/DETDA:DABA(3:2) CMS membrane. [ABSTRACT FROM AUTHOR]

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Two oligomers of lactic acid (OLAs), carboxyl (OLA-COOH) or hydroxyl (OLA-OH) end capped, were employed to modulate physical and mechanical properties of poly(lactic acid), PLA. Blends up to 25 wt.% by weight of OLAs were prepared by melt mixing. Mechanical, thermal and transport properties of the materials were tested as a function of OLA functional moieties and blend composition. Moreover, the effect of physical aging on structure and properties of blends was studied by storing the samples in controlled temperature and humidity conditions, up to 8 weeks. OLAs significantly affect mechanical properties of PLA; blends showed an interesting ductility even after aging, suggesting their use as flexible films. Moreover, gas transport and total migration properties of blends are suitable for packaging applications. [ABSTRACT FROM AUTHOR]

ABSTRACT The current work utilizes three separate techniques to study the physical aging process in amorphous poly(ethylene furanoate) (PEF), which is a recently introduced engineering thermoplastic with enhanced properties compared to petroleum-sourced poly(ethylene terephthalate). Differential scanning calorimetry aging experiments were conducted at multiple aging temperatures and times, and the resultant enthalpic recovery values compared to the theoretical maximum enthalpy loss evaluated from calculations involving extrapolation of the equilibrium liquid line. Density measurements reveal densification of the matrix for the aged versus unaged samples, and provide an estimate for the reduction in free volume for the aged samples. Complementary oxygen permeation and pressure-decay sorption experiments provide independent verification of the free volume reduction mechanism for physical aging in glassy polymers. The current work provides the first detailed aging study for PEF. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 389-399 [ABSTRACT FROM AUTHOR]

The structural relaxation (or physical aging) has been analyzed by means of fast scanning calorimetry for a random propylene- co -1-octene copolymer, in a wide range of annealing temperatures and times. For annealing temperatures well below T g only the structural relaxation is observed, and both the rate of enthalpy recovery and the peak temperatures related to the relaxation show a remarkable reduction with decreasing annealing temperatures. When the glass transition temperature is approached, although the structural relaxation is observed first, mesophase ordering is obtained at higher annealing times. The analysis of this mesophase ordering suggests homogeneous nucleation, and, in agreement with prior research in this field, the main feature is that the ordering in the glassy state requires prior completion of the enthalpy relaxation. [ABSTRACT FROM AUTHOR]

The ductile-brittle transition behaviour of organo modified montmorillonite-based Poly(lactic acid) films (PLA/o-MMT) was analysed using the Essential Work of Fracture (EWF) methodology, Small Punch Tests (SPT) and Enthalpy relaxation analysis. While the EWF methodology could only be applied successfully to de-aged samples, small punch test (SPT) was revealed as more effective for a mechanical characterization during the transient behaviour from ductile to brittle. According to differential scanning calorimetry (DSC) results, physical aging at 30°C of PLA/o-MMT samples exhibited slower enthalpy relaxation kinetics as compared to the pristine polymer. Although all samples exhibited an equivalent thermodynamic state after being stored one week at 30°C, significant differences were observed in the mechanical performances. These changes could be attributed to the toughening mechanisms promoted by o-MMT. [ABSTRACT FROM AUTHOR]

Rational design of fillers and polymers is of great importance to fabricate mixed matrix membranes (MMMs) with high performance. In this work, fluorinated metal-organic frameworks (KAUST-7 (also referred as NbOFFIVE-1-Ni)) were adopted as nanofillers to prepare MMMs through physically blending into the polymer of intrinsic microporosity (PIM-1). Benefiting from the features of porous KAUST-7, including well CO 2 affinity, distinctive pore characteristics (size, shape, and functionality) and strong intermolecular interactions with PIM-1, the achieved MMMs demonstrated increased CO 2 /CH 4 separation performance and improved anti-physical aging property. Specifically, with the assistance of KAUST-7, the CO 2 permeability and CO 2 /CH 4 (30:70 vol%) selectivity of the optimized MMMs increased up to 5928 Barrer and 23.5, corresponding to improvements of 50% of and 88% of the permeability and selectivity compared with the pristine membranes, respectively. Importantly, 100-h continuous separation test results confirmed the satisfying long-term stability of the prepared MMMs. Notably, the MMMs maintained 91% of the initial CO 2 permeability after 150 days (decreased only 539 Barrer), implying that the CO 2 permeability decrement is about 5-fold lower than that of the control PIM-1 membrane. These results suggest that the fabricated MMMs are promising candidates for CO 2 separation in practical applications. [Display omitted] • The CO 2 -philic KAUST-7 fillers were incorporated to PIM-1 for fabrication of MMMs. • The resultant MMMs exhibit enhanced CO 2 permeability and selectivity. • Long-term stable CO 2 /CH 4 separation and good antiaging performance were achieved. • Good interfacial compatibility between fillers and polymers results in the enhanced performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mechanical properties of PLA/PBAT after long-term physical aging were studied. • Elongation at break decreases from 257 % to 14 % after aging at 40 °C for 7 days. • Macroscopic modulus of PLA/PBAT increases with aging time. • Microscopic modulus and its distribution of PLA matrix increase with aging time. • DSC results reveal that PBAT has no impact on the physical aging of PLA matrix. Poly(lactic acid) (PLA) is a well-known biodegradable sustainable polyester but with intrinsic brittleness. PLA can be toughened through blending with immiscible rubbery polymers like biodegradable poly(butylene adipate- co -terephthalate) (PBAT). However, little was done to examine the effectiveness of the additives after long-term physical aging. Herein, the mechanical properties of PLA/PBAT (80/20) blends were measured by combining tensile tests and atomic force microscopy (AFM) based nanomechanical mapping after ageing at 40 °C for different periods. It is found that the elongation at break of the blends decreases dramatically from 257 % after compression molding to 14 % after aging for 7 days, and an equilibrium value is not yet reached. AFM nanomechanical mapping reveals that the microscopic Young's modulus distribution of PLA matrix broadens significantly with increasing aging time, reflecting the increase of heterogeneity and resulting in the embrittlement of the blends. This work raises the severe impact of physical aging on the mechanical properties of PLA based blends, which is usually overlooked but may limit their applications. [ABSTRACT FROM AUTHOR]

Biochar applied into the soil is recommended as an effective tool for increasing its properties and crop productivity. However, biochar can contain some potentially toxic compounds such as polycyclic aromatic hydrocarbons (PAHs). Moreover, during biochar production or environmental application (e.g. as soil fertilizer), more toxic PAHs derivatives containing nitrogen, oxygen or sulfur can be formed. There is a lack of information on how the environmental factors affect the bioavailability of such compounds during the long-term application of BC into the soil. In the presented studies the effects of physical (freeze-thaw cycles) and chemical aging (temperatures 60 °C and 90 °C) on the total and bioavailable content of PAHs and their derivatives were estimated. The results indicate that long-term (6 months) aging affected the physicochemical characteristic of biochars promoting the formation of new C and O-containing species on the BC surface increasing their polarity and hydrophilicity. Physical and chemical aging promoted the formation of compounds with higher molecular weight and a significant (up to 550 %) increase in the bioavailability of PAHs and their derivatives. The results of this study highlight the importance of the bioavailable fraction of PAHs and their derivatives for evaluation of the toxicity of aged biochar. [Display omitted] • biochar can contain some potentially toxic PAHs and more toxic PAHs derivatives. • There is a lack of information on their bioavailability during long-term experiment. • physical and chemical aging affected total and bioavailable PAHs and derivatives. • long-term (6 months) aging affected the physicochemical characteristic of biochar. • aging promoted the increased in the bioavailability of PAHs and their derivatives. [ABSTRACT FROM AUTHOR]

A facile, robust and scalable one-pot synthesis of easily processable, film-forming, shape persistent polymers became a great challenge in membrane separation technologies. Herein, we report for the first time a simple methodology of engineering off main chain ether-bond-free, ladderized, fluorinated aromatic polymers with rigid kink-structured backbones by polymerization of planar dibenzofuran (DBF) possessing multiple competitive reactive sites with carbonyl compounds. Five polymers incorporating rigid planar dibenzofuran isomer moieties with different bulky pendant trifluoromethyl- and aryl fragments were synthesized by one-pot, room temperature, non-stoichiometric superacid catalyzed step-growth polymerization. These solution processable aromatic polymers with ladderized, rigid kink-structured backbones provided membranes with tunable gas separations, physical aging resistance, and good mechanical and thermal properties. The membranes displayed CO 2 permeability between 203 and 401 Barrer and H 2 permeability between 210 and 472 Barrer, with CO 2 /CH 4 and H 2 /CH 4 selectivity close to 2008 Robeson's upper bound. Their gas permeability is due to a high FFV caused by packing of their kink-structured backbones, bulky pendant groups and to a strong interaction between CO 2 and the ring fused oxygen atoms in the polymeric structure. Physical aging, measured in 30–40 μm films after 500 days, resulted in permeability drops from 17% to 39% with improved selectivity. The results obtained also demonstrate the versatility of this synthetic strategy based on superacid catalyzed polymerization to fabricate well-defined macromolecules with designed shape-persistent architecture for advanced membrane applications. [Display omitted] • New aromatic fluoropolymers with ladderized, rigid, kink-structured backbones. • High performance functional polymers based on monomers with multiple reactive sites. • Rigid DBF isomer kink-structured fragments increase permeability and selectivity. • Combination of dibenzofuran moiety bulky fragments produced high FFV polymers. • Rigid kink-structured backbones of DBF poymers show aging resistant after 500 days. [ABSTRACT FROM AUTHOR]