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Cellulose nanocrystals (CNCs) have been blended into polylactic acid (PLA) to improve the polymer's properties. The dispersion of CNC in the matrix has a strong influence on the properties of the nanocomposites. In this study, PLA and CNC were compounded by a reactive extrusion process using dicarbonyl peroxide (DCP) as the free radical initiator. Isothermal and non-isothermal crystallization kinetics of the resulting nanocomposites were investigated to understand the effect of PLA-D-CNC on the crystallization of the materials. Nuclear magnetic resonance and Fourier transform infrared spectroscopy analyses confirmed the grafting of PLA onto CNC via reactive extrusion. The Avrami and Tobin model studies showed that the reactive extrusion product PLA-D-CNC exhibited much higher crystallization rates compared to neat PLA, PLA/CNC (without DCP), and PLA/DCP. The maximum crystallization rate temperature of PLA, PLA/CNC, and PLA/DCP was increased from ~100 to ~110[degrees]C for PLA-D-CNC. The results showed that CNC promoted PLA nucleation and crystallization at high temperatures under the action of DCP. Specifically, the maximum crystallization rate of PLA-D-CNC was 46 times higher than that of neat PLA. PLA-D-CNC showed a two-stage crystallization process, while the other three samples exhibited mostly single-stage processes. The much-enhanced crystallization of PLA-D-CNC was ascribed to the improved interaction between PLA and PLA-D-CNC and the homogeneous dispersion of CNC. Highlights * PLA chains were grafted onto CNC with the assistance of DCP free radicals. * PLA-grafted CNC facilitated heterogeneous nucleation of PLA. * Crystallization studies confirmed improved PLA crystallization in the presence of PLA-D-CNC. KEYWORDS cellulose nanocrystal (CNC), crystallization kinetics, dicumyl peroxide (DCP), polylactic acid (PLA), 1 | INTRODUCTION Polymers derived from renewable resources have seen increased use in the past decades due to their sustainable production and low impacts on the environment and human health. [...]

The morphology and orientation of polymer crystals are important factors which determine the performance of thin-film, polymer-based technologies such as organic electronic devices and gas separation membranes. Here, we utilize polymer-substrate epitaxy to achieve a highly oriented crystalline morphology during thin-film processing. To accomplish this, we employ matrixassisted pulsed laser evaporation (MAPLE), a slow physical vapor deposition process, to deposit linear polyethylene epitaxially atop a graphene substrate. Via MAPLE, we demonstrate the ability to achieve a film morphology comprised of well-aligned, edge-on crystalline lamellae. Furthermore, we show that MAPLE can be exploited to grow crystalline lamellae composed entirely of extended polymer chains which exhibit a near-equilibrium melting temperature. Our study demonstrates that MAPLE, as a bottom-up approach, can deposit polymer thin films with improved control over crystalline morphology. KEYWORDS epitaxial polymer crystallization, graphene, grazing-incidence x-ray diffraction, matrixassisted pulsed laser evaporation, melting, 1 | INTRODUCTION Enforcing the crystallization of polymers into a desired thin-film morphology remains a major scientific challenge. [4] Yet, the morphology is a critical factor determining the performance of [...]

Protein crystallization is important in structural biology, disease research and pharmaceuticals. It has recently been recognized that nonclassical crystallization--involving initial formation of an amorphous precursor phase--occurs often in protein, organic and inorganic crystallization processes.sup.1-5. A two-step nucleation theory has thus been proposed, in which initial low-density, solvated amorphous aggregates subsequently densify, leading to nucleation.sup.4,6,7. This view differs from classical nucleation theory, which implies that crystalline nuclei forming in solution have the same density and structure as does the final crystalline state.sup.1. A protein crystallization mechanism involving this classical pathway has recently been observed directly.sup.8. However, a molecular mechanism of nonclassical protein crystallization.sup.9-15 has not been established.sup.9,11,14. To determine the nature of the amorphous precursors and whether crystallization takes place within them (and if so, how order develops at the molecular level), three-dimensional (3D) molecular-level imaging of a crystallization process is required. Here we report cryogenic scanning transmission microscopy tomography of ferritin aggregates at various stages of crystallization, followed by 3D reconstruction using simultaneous iterative reconstruction techniques to provide a 3D picture of crystallization with molecular resolution. As crystalline order gradually increased in the studied aggregates, they exhibited an increase in both order and density from their surface towards their interior. We observed no highly ordered small structures typical of a classical nucleation process, and occasionally we observed several ordered domains emerging within one amorphous aggregate, a phenomenon not predicted by either classical or two-step nucleation theories. Our molecular-level analysis hints at desolvation as the driver of the continuous order-evolution mechanism, a view that goes beyond current nucleation models, yet is consistent with a broad spectrum of protein crystallization mechanisms. Cryo-STEM tomography of ferritin crystallization is used to reveal nonclassical evolution of crystalline order, indicating that it may be desolvation that drives the continuous evolution of order in crystallization., Author(s): Lothar Houben [sup.1] , Haim Weissman [sup.2] , Sharon G. Wolf [sup.1] , Boris Rybtchinski [sup.2] Author Affiliations: (1) Department of Chemical Research Support, Weizmann Institute of Science, Rehovot, [...]

Nonisothermal crystallization kinetics of poly(butylene terephthalate) (PBT)/glass fiber (GF) and PBT/epoxidized ethylene propylene diene rubber (eEPDM)/GF composites were investigated by differential scanning calorimetry (DSC) at a cooling rates of 2.5, 5, 10, and 20[degrees]C/min, respectively. Morphologies of samples were observed with scanning electron microscopy and polarized optical microscopy. The specimens were prepared by melt blending. Analyses of the melt crystallization data by various macrokinetic models such as Jeziorny-modified Avrami, Liu-Mo models, and Lauritzen-Hoffman equation revealed that GF accelerated the crystallization rate of PBT; furthermore, the eEPDM had two functions: on the one hand, eEPDM promoted PBT to form nuclei; on the other hand, eEPDM hindered the diffusion of polymer chains, but the nucleation effect exceeded the diffusion effect, thus, the eEPDM could increase the crystallization rate of PBT in PBT/eEPDM/GF. These results were further supported by the effective activation energy calculated by isoconversional method of Friedman., INTRODUCTION Poly(butylene terephthalate) (PBT), a semicrystalline thermoplastic polyester has excellent dimensional stability, high strength, chemical resistance, and fast rate of crystallization, and it is well suited for injection molding because [...]

The structure and composition of granites provide clues to the nature of silicic volcanism, the formation of continents, and the rheological and thermal properties of the Earth's upper crust as far back as the Hadean eon during the nascent stages of the planet's formation.sup.1-4. The temperature of granite crystallization underpins our thinking about many of these phenomena, but evidence is emerging that this temperature may not be well constrained. The prevailing paradigm holds that granitic mineral assemblages crystallize entirely at or above about 650-700 degrees Celsius.sup.5-7. The granitoids of the Tuolumne Intrusive Suite in California tell a different story. Here we show that quartz crystals in Tuolumne samples record crystallization temperatures of 474-561 degrees Celsius. Titanium-in-quartz thermobarometry and diffusion modelling of titanium concentrations in quartz indicate that a sizeable proportion of the mineral assemblage of granitic rocks (for example, more than 80 per cent of the quartz) crystallizes about 100-200 degrees Celsius below the accepted solidus. This has widespread implications. Traditional models of magma formation require high-temperature magma bodies, but new data.sup.8,9 suggest that volcanic rocks spend most of their existence at low temperatures; because granites are the intrusive complements of volcanic rocks, our downward revision of granite crystallization temperatures supports the observations of cold magma storage. It also affects the link between volcanoes, ore deposits and granites: ore bodies are fed by the release of fluids from granites below them in the crustal column; thus, if granitic fluids are hundreds of degrees cooler than previously thought, this has implications for research on porphyry ore deposits. Geophysical interpretations of the thermal structure of the crust and the temperature of active magmatic systems will also be affected. Thermobarometry and diffusion modelling in quartz crystals show that some granites may crystallize at much lower temperatures than we had thought, possibly explaining observations of cold magma storage., Author(s): Michael R. Ackerson [sup.1] [sup.2] , B. O. Mysen [sup.1] , N. D. Tailby [sup.3] , E. B. Watson [sup.2] Author Affiliations: (1) Geophysical Laboratory, Carnegie Institution of Washington, [...]

Author(s): Rodrigo E. Guerra [1]; Colm P. Kelleher [1]; Andrew D. Hollingsworth [1]; Paul M. Chaikin (corresponding author) [1] The best understood crystal ordering transition is that of two-dimensional freezing, [...]

Abstract: At Kellys Mountain, Cape Breton Island, Nova Scotia, the late Neoproterozoic Glen Tosh formation (a low-grade metapsammite-metapelite unit of the George River Metamorphic Suite) has been intruded by diorite, [...]

Atoms of a metal alloy have been tracked as they form crystal nuclei -- the first ordered clusters of atoms or molecules produced during crystallization. The findings might help to develop a general nucleation theory. Observations of crystal nucleation., Author(s): Peter G. Vekilov Author Affiliations: Crystallization tracked atom by atom Nucleation is the earliest stage of crystallization, in which atoms or molecules dispersed in a crystallization medium first come [...]

Although Poly(lactic acid) (PLA) possesses many desirable properties, above all biodegradability, its heat deflection temperature is too low for many desirable applications. Similarly, to any other polymers, also for PLA the physical and mechanical properties in the solid state depend on the morphology and crystallinity degree, which in their turn are determined by the thermomechanical history experienced during solidification. A large crystallinity degree is highly desirable to increase the heat resistance of PLA but is rather difficult to reach during injection molding due to the very slow crystallization kinetics of this material. In this work, the crystallization kinetics of an injection molded PLA grade was assessed in function of the thermal history by using calorimetric analysis. The cold crystallization kinetics (starting from the amorphous glassy sample) turned out to be faster than melt crystallization kinetics. Following the indications gained from crystallization kinetics, some samples were injection molded imposing different thermal histories. The effect of molding conditions on crystallinity was determined. This finding was adopted to develop a post-molding stage which allows obtaining crystalline samples in times much shorter (of a factor about two) with respect to samples injection molded in a hot mold kept at temperatures close to the maximum crystallization rate., INTRODUCTION Physical, thermal, and mechanical properties of thermoplastic polymers are strongly dependent on the crystalline structure and morphology. For this reason, crystallization is a major research interest in the field [...]

Poly[vinylidenefluoride-co-(tetrafluoroethylene)J (P(VDF-TeFE)) exhibited clear spherulitic texture with negative birefringence. The number and growth rates of the spherulites decreased at high crystallization temperature than at low crystallization temperature. Nonetheless, overall larger spherulites were found at high crystallization temperature and the brightness of the spherulites increased very fast at low crystallization temperature, thereafter it seemed as diminution of birefringence. AFM was used to investigate the impact of organo modified nanodiamond(ND) on spherulitic textures, lamellar thickness, and thickness distribution of P(VDF-TeFE) copolymer. Poly[ethylene-co-(tetrafluoroethylene)] (ETFE) also confirmed spherulites structure and the boundaries could be clearly observed. By incorporation of the organo modified nanodiamond (ND) and organo-modified montmorillonite (MMT) in fluropolymer matrix, it was found that spherulitic texture was seriously disordered and their nanohybrids was found only to have poorly developed spherulite structure. Both of the nanohybrids samples show better crystallization temperature as compared to their neat copolymer samples. Furthermore, the incorporation of nanoparticles decreased the size of the spherulites., INTRODUCTION The enhancement of polymer spherulites from the melt, when observed with a polarized light microscope, is a phenomenon that is really attractive in its beauty and apparent simplicity [1]. [...]

Composites of polypropylene (PP) and multi-walled carbon nanotubes (MWCNTs) were prepared via melt-mixing utilizing Li-salt of 6-amino heaxanoic acid (Li-AHA) modified MWCNTs in the presence of a compatibilizer (polypropylene-g-maleic anhydride; PP-g-MA). Improved interaction between the anhydride group of PP-g-MA and the amine functionality of Li-AHA was confirmed via FTIR and Raman spectroscopic analysis. A higher glass transition temperature ([T.sub.g]) of the PP phase has been observed in these composites as compared to pristine MWCNTs-based composites. The crystallization temperature ([T.sub.c]) of the PP phase was increased as a function of pristine MWCNTs concentration in PP/MWCNTs composites indicating heteronucleating action of MWCNTs. However, [T.sub.c] value was decreased in the presence of Li-AHA modified MWCNTs indicating the adsorbed Li-AHA on the MWCNTs surface. Moreover, [T.sub.c] value was higher in the presence of Li-AHA modified MWCNTs with PP-g-MA as compared to that of without PP-g-MA, suggesting the desorbed Li-AHA from the MWCNTs surface due to melt-interfacial reaction. Further, MWCNTs were extracted by hot vacuum filtration technique from PP/MWCNTs composites containing Li-AHA and PP-g-MA. The isothermal crystallization kinetics showed a variation in crystallization behavior of the PP phase in the corresponding composites as compared to the 'extracted MWCNTs.', INTRODUCTION The discovery of carbon nanotubes (CNTs) [1] have led to the development of CNTs-based materials for various applications viz.; EMI shielding [2], super capacitors, memory devices [3], lithium-ion secondary [...]

Ultrahigh molecular weight polyethylene (UHMWPE) is usually difficult to be melt processed due to severe intermolecular entanglement in its melt. In this work, we reported the development of a poly(amido amine) (PAMAM) dendrimer (G1) and its derivatives with different terminal groups which showed promising feasibility for aiding UHMWPE melt processing. The rheological, crystalline, and mechanical properties of the blends were investigated comprehensively. The addition of the dendritic modifiers to the UHMWPE matrix resulted in a significant decrease in melt viscosity, thus an obvious enhancement of the processability. The dynamic analysis of the mechanical properties and rotation-rheological test indicated a disentanglement effect of the UHMWPE melt molecules was generated by the PAMAM dendrimer (G1) and its derivatives. Furthermore, the PAMAM dendrimer (G1), as an internal lubricant, was uniformly distributed in the UHMWPE matrix. The heteronucleation effect of the PAMAM dendrimer (G1) with its derivatives led to a higher degree of crystallinity, smaller crystallites in the matrix and enhanced tensile strength in the UHMWPE blends., INTRODUCTION Ultra high molecular weight polyethylene (UHMWPE) is a type of linear, high-density, semi-crystalline polymer that offers many excellent material characteristics, including high chemical inertness, low friction coefficient, high impact [...]

Archaean komatiites (ultramafic lavas) result from melting under extreme conditions of the Earth's mantle. Their chemical compositions evoke very high eruption temperatures, up to 1,600 degrees Celsius, which suggests even [...]

The present article deals with the differential thermal analyses (DTA) study of Se-Te glasses containing Sn. DTA runs are taken at six different heating rates (5, 10, 15, 18, 20, and 22 K [min.sup.-1]). The crystallization data are examined in terms of modified Kissinger, Mahadevan method, and Augis and Bennett approximation for the non-isothermal crystallization. Results of DTA under non-isothermal conditions on the glasses of the [Se.sub.80][Te.sub.20-x][Sn.sub.x] (x = 3 and 9) are reported and discussed at different heating rates. The glass transition temperatures ([T.sub.g]), the onset crystallization temperatures ([T.sub.c]), and the peak temperature of crystallization ([T.sub.p]) were found to be dependent on the compositions and the heating rates. From the dependence on heating rates of ([T.sub.g]) and ([T.sub.p]) the activation energy for glass transition ([E.sub.g]) and the activation energy for crystallization ([E.sub.c]) are calculated and their composition dependence discussed. PACS Nos.: 81.70.Pg, 65.60.+a, 61.43.Dq. Nous presentons ici des etudes d'analyse thermique differentielle (DTA) de verres Se-Te contenant du Sn. Les mesures DTA sont prises a six differents taux de chauffage (5,10,15,18, 20 et 22 K [min.sup.-1]). Nous examinons les donnees de cristallisation en utilisant les methodes de Kissinger et de Mahadevan et l'approximation de Augis et Bennett pour une cristallisation non isotherme. Nous presentons et discutons, a differents taux de chauffage, nos resultats DTA sous condition non isotherme pour les verres [Se.sub.80][Te.sub.20-x][Sn.sub.x] (x = 3 et 9). Nous observons que la temperature de transition verre ([T.sub.g]), la temperature du debut de la cristallisation ([T.sub.c]) et la temperature pic de cristallisation ([T.sub.p]) dependent de la composition et du taux de chauffage. A partir de la dependance sur le taux de chauffage de [T.sub.g] et de [T.sub.p], nous calculons l'energie d'activation ([E.sub.g]) pour la transition verre et l'energie d'activation pour la cristallisation ([E.sub.c]) et nous discutons de leur dependance sur la composition. [Traduit par la Redaction], 1. Introduction Chalcogenide glasses are made up of group VI elements (S, Se, and Te) of the periodic table. These glasses behave as semiconducting materials. During the past year, an [...]

Tri-(butanediol-monobutyrate) citrate (TBBC) as a new plasticizer for poly(lactic acid) (PLA) was synthesized via a two-step esterification. The chemical structure of TBBC was characterized by ¹H-nuclear magnetic resonance. The studies on solubility parameters, transparence, and storage stability indicated the good miscibility between PLA and TBBC. The glass transition, crystallization, thermal, and mechanical properties of PLA plasticized by TBBC were evaluated. With an increase in TBBC content, the glass transition temperature ([T.sub.g]), melting point ([T.sub.m]), and the cold crystallization temperature ([T.sub.cc]) of plasticized PLA gradually shifted to a lower temperature. The elongation at break and flexibility were greatly improved by the addition of TBBC. After 30 days of storage, PLA plasticized with up to 20 wt% of TBBC exhibited good storage stability and remained the original transparence and mechanical properties. The flexibility of PLA/TBBC films can be tuned by changing TBBC content. The corresponding crystalline morphology and structure were investigated by Polarizing optical microscope and X-ray diffraction as well. This study revealed that TBBC was miscible with PLA and may therefore be a promising plasticizer for PLA-based packaging materials. POLYM. ENG. SCI., 55:205-213, 2015. [C] 2014 Society of Plastics Engineers, INTRODUCTION The environmental and food safety problems have aroused people's concern about biodegradable materials [1]. Biodegradable polymers are considered as food packaging materials to solve serious ecological problems caused by [...]

A melt-extruded method has been used to prepare blend membranes of Perfluorosulfonic Acid Polymer (PFSA) and Perfluorocarboxylic Acid Polymer (PFCA) with different combination ratios. Fourier Transform Infrared (FT-IR) and X-ray Diffraction (XRD) analyses have showed that the chemical structure and crystallization behaviour of both polymers remained unchanged in the blend membrane, and the crystallinity has been increased for the blend membrane with a higher weight fraction of PFCA. According to the results obtained from Scanning Electron Microscope (SEM), PFSA and PFCA polymers are well compatible, forming mixed aggregates containing both sulphonyl and carboxyl ions. Surprisingly, a membrane containing a 50:50 ratio of PFSA/PFCA has showed microphase separation, and it possesses the smallest ionic cluster size among all the blend membranes prepared, as illustrated by the Small Angle X- Ray Scattering (SAXS) analysis. In addition, when the PFCA content was increased, the ion exchange capacity (IEC) for blend membranes remained the same, while their water uptake and proton conductivity have decreased rapidly. Compared with the PFSA/PFCA two-layered membrane, this PFSA/blend/PFCA membrane not only maintained respectable electrolysis property, also exhibited significantly higher peel strength, especially after the hydrolization process; plus, it has showed excellent resistance to the peeling damage under the operational conditions of chlor-alkali electrolytic cells., INTRODUCTION Fluorinated polymers containing pendant side chains are receiving greater and greater interest in industrial applications because of their remarkably high conductivity and outstanding thermal and chemical resistance [1-5]. Perfluorosulfonic [...]

The isothermal crystallization kinetics of nylon 6/graphene (NG) composites prepared by in situ polymerization was investigated by differential scanning calorimetry. The Avrami equation was used to study the crystallization kinetics. Comparing with nylon 6, it is found that the NG composites (NG-0.1, NG-0.5, and NG-1.0, where the number describes the wt% content of graphene) had higher crystallization rates; the crystallization rate increased remarkably with 0.1 wt% graphene. However, too many crystallization nuclei could not accelerate the crystallization process effectively. The [t.sub.max] values obtained from the plots of heat flow versus time were in agreement with the [t.sub.max] values calculated from the half time of crystallization when the graphene content was lower than 1.0 wt%, which means that the values of the Avrami parameters calculated from the half time of crystallization might be in better agreement with the actual crystallization mechanism than that determined from the Avrami plots. The n values of the NG composites ranged between 1.1 and 1.8, which can be interpreted as meaning both one-dimensional and two-dimensional crystallization growth occurred during isothermal crystallization process. The activation energies, which were determined by the Arrhenius' method, varied within the range from -188 to -142 kJ/mol., INTRODUCTION In 2004, single layers of graphene were successfully prepared by Geim and co-workers at Manchester University in a simple experiment [1], As a new material, the modification of graphene/graphene [...]

Thermoplastic carbon fiber fabric reinforced composites (CFFRCs) were prepared using a novel fast manufacturing process with a low viscosity polymerizable cyclic butylene terephthalate (CBT) resin. Structure and properties of the composites altered by thermal annealing were investigated to develop appropriate post processing of the CFFRCs for fast production and lowering the processing cost. Annealing at 200°C for 120 min resulted in improved mechanical properties and thermal stability of the polymerized CBT (pCBT) based on differential scanning calorimetry, wide-angle X-ray diffraction, and thermo gravimetric analysis. The tensile strength of the CFFRC compression molded at 250°C for 2 min was 440 MPa and that of the CFFRC annealed at 200°C for 120 min after compression molding was 500 MPa, which is an improvement of 550 and 625% relative to the pCBT matrix, respectively. In addition, the thermal stability of the CFFRC annealed at 250°C for 120 min improved by 10°C. Therefore, tensile strength and thermal stability of the manufactured CFFRC can be improved by using the appropriate annealing conditions., INTRODUCTION Worldwide interest in energy reduction is increasing because of global issues, such as global warming, carbon emission, and inflation of oil prices, and weight savings in automobiles represent one [...]

Crystallization of polycarbonate (PC) was attempted by a precipitated method in a ternary system of PC/solvent/nonsolvent. Chloroform was used as a solvent, and isopropanol was used as a nonsolvent. Crystallization of PC was clearly observed as a powdery state when chloroform/isopropanol mixtures were prepared by 68/32 and 61/39 vol%. Crystallinity of PC was evaluated by differential scanning calorimeter and X-ray diffractometer. As the difference of solubility parameters between PC and binary solvent/nonsolvent mixtures became smaller, the relative crystallinity of PC was increased. The highest degree of PC crystallization was obtained when chloroform/isopropanol was mixed by 61/39 vol%. Subsequently, crystallized PC was used as a filler to high-density polyethylene (HDPE) composite. HDPE composite incorporated by crystallized PC filler improved its mechanical and thermal properties. Flexural modulus was increased from 620 to 990 N/[mm.sup.2], and flexural strength was increased from 720 to 1080 N/[mm.sup.2]. And heat deflection temperature measurement and flammability test supported the enhancement of thermal property when crystallized PC was added to HDPE composite up to 40 wt%., INTRODUCTION Plastic materials have been widely used in construction and automotive industries. To improve its thermal and mechanical properties, plastic materials could be reinforced by additive fillers [1-3]. Filler can [...]

The evolution of polyethylene/organoclay nanocomposite microstructure via shear and extentional flow fields was studied by tracing rheological behavior and nonisothermal crystallization kinetics. Although studying microstructure formed through flow fields, two phenomena were noticed: the breaking of three-dimensional (3D) network containing filler-filler, filler-matrix, and matrix-matrix interactions, and organoclay platelets orientation. Utilizing nonlinear viscoelastic measurements and thermal analyses, it was proven that clay alignment was present only in large enough shear flows and all elongational flows. It was observed that regardless of the type of flow field and its magnitude, due to the breaking of 3D network, the extent of crystallization can be increased. The half-lives of the crystallization of film samples and those samples subjected to large enough shear rates for clay platelets to be aligned decreased, proving the effect of clay orientation on crystallization rate increment. Based on endotherms observed through melting behavior studies of samples, it was proven that in elongation and large amplitude shear flows, clay orientation had resulted in forming thicker crystalline lamellae, likely because of forcing the adjacent polymer chains to align with the clay platelets., INTRODUCTION Polymer-layered silicate (PLS) nanocomposites have attracted considerable attention due to their academic and industrial importance. They have shown dramatic improvements in physical-mechanical, thermal, and barrier properties with a small [...]

Metastability effects because of atmospheric exposure, high purity gasses, and deionized water in hydrogenated microcrystalline silicon thin films with different crystalline volume fractions were studied using well accepted steady-state characterization methods of dark conductivity, steady-state photoconductivity, steady-state photocarrier grating (SSPG) and dual beam photoconductivity (DBP) methods. A standard measurement procedure has been established before using the steady state methods, in which a steady state condition of dark conductivity was established by monitoring the time dependence of dark conductivity. Samples deposited on smooth glass and rough glass substrates exhibit similar reversible and irreversible changes in the properties of microcrystalline silicon film. A reliable correlation of reversible and irreversible changes indicate that dark conductivity and photoconductivity values increase, sub-bandgap absorption spectrum obtained from DBP method decrease and correspondingly minority carrier diffusion lengths obtained from the SSPG method increase in the metastable state in various amount for microcrystalline films with crystalline volume fraction, [I.sup.RS.sub.C] > 0.30. Amorphous silicon and microcrystalline silicon films with [I.sup.RS.sub.C] < 0.30 do not show detectable metastable changes as samples exposed to atmospheric condition as well as high purity oxygen gas and deionized water. PACS Nos.: 73.61.Jc, 73.63.Bd, 73.50.Pz, 72.80.Ng. Nous utilisons des methodes de caracterisation stationnaire bien acceptees, comme la conductivite en obscurite, la photoconductivite stationnaire, la photoconductivite stationnaire par interferometrie laser (SSPG) et la photoconductivite modulee a deux faisceaux (DBP), afin d'etudier l'effet de la metastabilite dans des films minces de silicium microcristallin hydrogenes, suite a l'exposition a l'atmosphere, aux gaz de haute purete et a l'eau de-ionise. Avant d'utiliser ces methods stationnaires, nous avons developpe une procedure standard de mesure, dans laquelle la condition stationnaire de conductivite en obscurite est verifiee en observant la dependance en temps de la conductivite en obscurite. Les echantillons deposes sur des surfaces douces et rudes de substrats de verre montrent les memes changements reversibles et irreversibles dans les proprietes microcristallines des films de silicium. Une correlation fiable des changements reversibles et irreversibles des proprietes des films microcristallins indique que les valeurs de conductivite en obscurite et de photoconductivite augmentent et que le spectre d'absorption sous la bande interdite obtenu de SSPG augmente dans les films microcristallins en etat metastable pour lesquels la fraction cristalline en volume [I.sup.RS.sub.C] > 0.3. Les films de silicium amorphes et microcristallins avec [I.sup.RS.sub.C] < 0.3 ne montrent aucun changement metastable detectable lorsque les echantillons sont exposes aux conditions atmospheriques, a l'oxygene pur et a l'eau de-ionisee. [Traduit par la Redaction], 1. Introduction Upon exposure of microcrystalline silicon (μc-Si:H) thin films to room ambient, water vapour, deonized water, or to different gas atmospheres, these materials frequently show reversible (metastability) and irreversible [...]

Low thermal budget rapid thermal annealing is a promising method of forming highly crystalline silicon thin films on silicon substrates for heterojunction solar cells. In this work, the extent of crystallization was examined by Raman and ultraviolet reflectance spectroscopy, and ellipsometry was used to derive film optical properties. Solar cells were fabricated and analyzed using dark and illuminated current-voltage characteristics, external quantum efficiency, and solar simulator measurements with device efficiency approaching 14%. PACS Nos.: 88.40.jj, 78.66.Db, 78.40.Fy. Le recuit thermique rapide a faible budget thermique est une methode prometteuse pour fabriquer des films minces de silicium hautement cristallin sur des substrats de silicium, pour faire des cellules solaires heterojonctions. Nous examinons ici le niveau de cristallisation par spectroscopie de reflectance Raman et UV et un ellipsometre est utilisee pour determiner les proprietes optiques du film. Nous fabriquons les cellules solaires et nous les analysons en mesurant les caracteristiques courant-voltage en obscurite et sous illumination et le rendement quantique externe et par des mesures solaires simulees avec un rendement approchant 14 %. [Traduit par la Redaction], 1. Introduction Amorphous silicon (a-Si:H) heterojunctions on crystalline silicon (c-Si) substrates have received much interest among the photovoltaic research community. The classic c-Si/a-Si:H structure includes an ultrathin (2-5 nm thick) [...]

We have investigated the preparation of crystalline germanium films by the solid phase crystallization (SPC) of amorphous germanium (a-Ge) precursor on single crystalline silicon substrates. The a-Ge precursor easily incorporates the impurities from the surface exposed to the air, and the impurities affect the crystallinity after the SPC. In the a-Ge precursor prepared by Knudsen-cell evaporation, the preferential crystalline growth following the Si substrates is disturbed by the high density of impurities and the random crystalline structures are formed. The a-Ge precursors prepared by electron beam evaporation have high impurity concentrations only near the surface because the impurity diffusion is slow because of the relatively high density. The preferential growth is successfully obtained in a-Ge precursor prepared on n-type Si substrates, although the random crystallization is slightly observed on p-type Si substrates. By sufficiently reducing the impurity concentrations by avoiding the air exposure, the preferential growth can be promoted on p-type Si substrates. The impurity incorporation because of the air exposure is sufficiently reduced for the preferential growth by covering a-Ge with a-Si blocking layers. This method is effective for future practical applications of SPC Ge films. PACS Nos.: 61.43.Dq, 73.61.Jc, 73.50.Pz. Nous etudions la preparation de films cristallins de germanium en phase solide (SPC) a partir d'un precurseur de Germanium amorphe (a-Ge) sur un substrat fait d'un monocristal de silicium. Le precurseur de a-Ge incorpore des impuretes a partir de sa surface exposee a l'air et ces impuretes affectent la cristallinite apres la SPC. Dans les precurseurs de a-Ge prepares en cellule d'evaporation de Knudsen, la croissance cristalline preferentielle suivant le substrat de Si est perturbee par la haute densite d'impuretes et des structures cristallines aleatoires se forment. Le precurseur prepare par evaporation EB a une haute concentration d'impuretes seulement pres de la surface, parce que la diffusion des impuretes est lente, consequence de la relativement haute densite. On obtient la croissance preferentielle dans le precurseur de a-Ge prepare sur substrat de Si de type n, meme si la cristallisation aleatoire s'observe un peu sur des substrats de Si de type p. En reduisant suffisamment la concentration des impuretes dues a l'exposition a l'air, la croissance preferentielle devient possible sur les substrats de type p. L'incorporation d'impuretes dues a l'exposition a l'air est suffisamment reduite pour la croissance preferentielle en couvrant le a-Ge avec des couches bloquantes de a-Si. Cette methode est efficace pour de futures preparations de films de Ge par SPC. [Traduit par la Redaction], 1. Introduction Bulk-type silicon (Si) solar cells are a major part of the solar cell production in the world. However, higher energy conversion efficiency and lower production cost are required [...]

Solid phase crystallization of amorphous silicon films (a-Si:H) deposited by gas-jet electron beam plasma chemical vapor deposition method and annealed at 700°C in vacuum has been investigated. This method provides high deposition rates (up to 2.3 nm/s) of a-Si:H thin films in a standard vacuum chamber. The effects of varying the substrate temperature from 190 to 415°C on the structural and optical properties of the as-deposited amorphous films and postannealed nanocrystalline films have been investigated. The crystallite size was determined by X-ray diffraction (about 5-8 nm) and agrees with that obtained from Raman scattering. The estimated degree of crystallinity was 45%-59%. Optical transmission spectra were recorded to investigate the optical properties and thickness of the silicon thin films. The refractive index and optical band gap data was obtained for both as-deposited amorphous and post-annealed nanocrystalline silicon. The behavior of the refractive index of nanocrystalline silicon depending on the substrate temperature is correlated with the crystalline volume fraction. a-Si:H films obtained at low temperatures have larger crystallite size and better crystallinity after annealing. PACS Nos.: 73.61.Jc, 73.63.Bd, 78.66.Jg. Nous etudions la cristallisation en phase solide de films de silicium amorphe (a-Si:H) fabriques par depot chimique en phase vapeur avec faisceau de plasma et jet electronique, avant un recuit a 700°C, le tout dans le vide. Cette methode donne un fort taux de deposition (jusqu'a 2.3 nm/s) de a-Si:H dans une chambre a vide standard. Nous etudions l'effet de varier la temperature du substrat de 190 a 415°C sur les proprietes structurelles et optiques des films tels que deposes avant recuit et des films nano-cristallises apres recuit. Nous determinons la grosseur des cristallites par XRD (environ 5-8 nm) et elle correspond aux resultats par diffusion Raman. La cristallinite varie entre 45 % et 59 %. Nous enregistrons les spectres de transmission optique pour etudier les proprietes optiques et l'epaisseur des films de Si. Nous obtenons l'indice de refraction et les donnees sur la bande interdite optique des films tels que deposes et apres recuit. La dependance sur la temperature du substrat de l'indice de refraction est correlee avec la fraction cristalline en volume. Les films de a-Si:H obtenus a basse temperature ont des cristallites plus grosses et une meilleure cristallinite apres recuit. [Traduit par la Redaction], 1. Introduction In recent years, hydrogenated silicon films with a two-phase structure consisting of silicon nanocrystals (nc-Si) in a silicon amorphous matrix have attracted more and more attention. This material [...]

Flash lamp annealing (FLA) of micrometre-order thick amorphous silicon (a-Si) films can induce explosive crystallization (EC), high-speed lateral crystallization driven by the release of latent heat. We develop multi-pulse FLA system, which emits a quasi-millisecond pulse consisting of a number of subpulses. The emission frequency of the subpulses can be systematically controlled, and the emission of subpulses leads to the periodic modulation of the temperature of a Si film and the resulting formation of macroscopic stripe patterns. The relationship between a subpulse emission frequency and the width of the macroscopic stripe patterns yields EC velocity. Two kinds of EC modes can be observed, depending on the methods of precursor a-Si deposition and (or) a-Si film thickness. PACS Nos.: 81.10Jt, 81.40.Ef, 88.40.jj. Le recuit par lampe a decharge (FLA) de films de silicium amorphe (a-Si) peut causer une cristallisation spontanee (explosive) (EC) ou une cristallisation laterale induite, soutenue par le rejet de chaleur latente. Nous developpons un systeme de recuit par lampe a decharge multi-pulse qui emet des impulsions presque milliseconde consistant en un nombre de sousimpulsions. La frequence d'emission de ces sous-impulsions peut etre controlee et l'emission de ces sous- impulsions mene aune modulation de la temperature du film de Si, d'oU il resulte la formation d'un patron en bandes macroscopiques. La relation entre la frequence d'emission des sous-impulsions et la largeur de ces bandes donne la vitesse de EC. Nous observons deux types de modes EC, dependant de la methode de deposition du precurseur Si et (ou) de l'epaisseur du film de a-Si. [Traduit par la Redaction], 1. Introduction Thin-film crystalline Si (c-Si) is of great interest as a photovoltaic material because of the possibility of high efficiency and efficient material usage. Of a variety of methods [...]

Silicon carbide (SiC) is a promising material for the fabrication of optoelectronic devices. In the amorphous state physical-vapor-deposited SiC is already an essential part of the production of electron beam liquid phase crystallized silicon absorbers, because of its good wettability for the silicon melt. The resulting polycrystalline thin film absorbers exhibit excellent electrical properties (B. Eggleston et al. MRS Online Proc. Libr. 1426, 251 (2012)) and demonstrate the potential of this technology (J. Dore et al. IEEE J. Photovolt. 4, 33 (2014)). A drawback of amorphous SiC interlayers is their poor optical properties. In this work we investigate two different approaches. Firstly, we show how those properties can be improved by depositing Si[C.sub.x] [O.sub.y] layers to enhance the transmittance while maintaining the wettability. Secondly, the laser crystallization of amorphous silicon- carbon compounds is studied as a function of their composition and the applied laser fluence. Compared to the amorphous SiC layers a clear reduction of the absorption coefficient was achieved upon laser annealing without losing wettability. Raman backscattering measurements showed that laser annealing of reactively sputtered amorphous SiC leads to a material with a vibrational mode at 770 [cm.sup.-1] that is indicative of 6H-SiC. Atomic force microscopy measurements of those crystalline layers also show an ordered triangular grain structure, which was not observed in the amorphous material. It is shown that segregation effects are strongly affected by the stoichiometry and the applied laser fluence. PACS Nos.: 77.55.df, 77.84.Bw, 81.10.Jt. Le carbure de silicium (SiC) est un materiau prometteur pour la fabrication de dispositifs optoelectroniques. Dans son etat amorphe obtenu par depot physique de vapeur, SiC joue deja un role essentielle dans la production d'absorber au silicium poly-cristallise en phase gazeuse par faisceau d'electrons, a cause de sa grande mouillabilite pour le silicium fondu. Les absorbeurs en films minces poly-cristallins qui en resultent ont d'excellentes proprietes electriques (B. Eggleston et al. MRS Online Proc. Libr. 1426, 251 (2012)) et demontrent le potentiel de cette technologie (J. Dore et al. IEEE J. Photovolt. 4, 33 (2014)). Les proprietes optiques sont une des faiblesses des couches intermediaires de SiC. Nous etudions ici deux approches differentes pour y remedier. D'abord, nous montrons que le depot de couches de Si[C.sub.x][O.sub.y] augmente la transmittance, tout en conservant la mouillabilite, Ensuite, nous etudions la cristallisation par laser des composes amorphes de silicium-carbone en fonction de leur composition et du debit du laser. Comparant avec les couches de SiC amorphe, nous notons une diminution sensible du coefficient d'absorption suivant un recuit par laser, sans perte de mouillabilite. Des mesures Raman arriere montrent que le recuit par laser du SiC amorphe evapore par reaction donne un materiau avec un mode vibrationnel a 770 [cm.sup.-1], indication d'un compose 6H-SiC. Les mesures par microscopie a force atomique indiquent que les couches cristallines ont une structure de grain triangulaire, qui n'est pas observee dans le materiau amorphe. Nous montrons que les effets de segregation sont fortement affectes par la stoehiometrie et par le debit du laser. [Traduit par la Redaction], 1. Introduction In the production of solar cell absorbers by means of electron beam assisted liquid phase crystallization (LPC) it is necessary to overcome some technological challenges. An important aspect [...]

The influence of the used substrate and the boron doping concentration of the charge-transport properties of solid-phase crystallized polycrystalline silicon (poly-Si) is explored. The samples were characterized using temperature dependent transport measurements to determine mobility, carrier concentration, and conductivity. While Arrhenius plots of the hole concentration cannot be used to determine the position of the Fermi energy, a detailed analysis of the temperature dependent carrier concentration shows a Meyer-Neldel and an anti-Meyer-Neldel rule. Charge transport in poly-Si on SiN coated Borofloat glass with a boron concentraion [B] < [10.sup.16] [cm.sup.-3] is limited by phonon scattering. On the other hand, for all poly-Si samples on Corning glass and poly-Si on SiN coated Borofloat glass with [B] > [10.sup.16] [cm.sup.-3] charge-carrier transport is governed by thermionic emission over potential barriers. The data are discussed in terms of the Baccarani transport model. PACS Nos.: 72.20.-i, 72.80.Cw, 71.55.Jv. Nous explorons l'influence du substrat utilise et de la concentration du dopage en bore, sur les proprietes de transport de charge du silicium poly-cristallin (ploy-Si) cristallise en phase solide. Les echantillons sont caracterises en utilisant des mesures de transport dependant de la temperature pour determiner la mobilite, la concentration de porteurs et la conductivite. Alors que le graphique d'Arrhenius de la concentration de trous ne peut pas etre utilise pour determiner l'energie de Fermi, une etude detaillee de la dependance en temperature de la concentration de porteurs montre une regle de Meyer-Neldel et une regle anti-Meyer-Neldel. Le transport de charge utilisant du verre Borofloat couvert de poly-Si sur SiN, avec une concentration de bore [B] < [10.sup.16] [cm.sup.-3], est limite par la diffusion avec les phonons. D'un autre cote, pour tous les echantillons de poly-Si sur du verre Corning et de verre Borofloat couvert de poly-Si sur SiN, avec [B] > [10.sup.16] [cm.sup.-3], le transport des porteurs de charge est controle par l'emission thermioinique au dessus des barrieres de potentiel. Nous analysons les donnees a partir du modele de transport de Baccarani. [Traduit par la Redaction], 1. Introduction Polycrystalline silicon (poly-Si) has received attention as an electronic material to replace amorphous silicon in thin-film solar cells. The superior optical and electronic properties promise a substantial improvement [...]

We examine the dependence of the crystalline volume fraction on the mean crystallite size for hydrogenated nanocrystalline silicon based photovoltaic solar cells; this work builds upon an earlier study by Schmidt et al. (Mater. Res. Soc. Symp. Proc. 1536 (2013)). For each photovoltaic solar cell considered, the X-ray diffraction and Raman spectra are measured. Through the application of Scherrer's equation, the X-ray diffraction results are used to determine the corresponding mean crystallite sizes. Through peak decomposition, the Raman results are used to estimate the corresponding crystalline volume fraction. Plotting the crystalline volume fraction as a function of the mean crystallite size, it is found that larger mean crystallite sizes tend to favor reduced crystalline volume fractions. The ability to randomly pack smaller crystallites with a greater packing fraction than their larger counterparts was suggested as a possible explanation for this observation. PACS Nos.: 61.05.cp, 78.30.Ly, 68.37.-d. Nous examinons la dependance de la fraction cristalline en volume sur la grosseur moyenne des cristallites (grains) dans des cellules solaires a base de silicium nanocristallin hydrogene. Ce travail est base sur une etude anterieure par Schmidt et al. (Mater. Res. Soc. Symp. Proc. 1536 (2013)). Nous mesurons la diffraction X et le spectre Raman pour chaque cellule photovoltaique etudiee. Par l'equation de Scherrer, les mesures de diffraction X permettent de determiner la grosseur des cristallites. Via une decomposition spectrale, les resultats Raman nous permettent d'estimer la fraction cristalline en volume correspondante. Le graphique de la fraction volumique en fonction de la grosseur des cristallites indique que de plus grosses crystallites correspondent a une plus petite fraction cristalline en volume. La capacite d'entasser au hasard de plus petites cristallites avec un plus grand coefficient de tassement que ce qu'il est possible d'obtenir avec des cristallites plus grosses, est une explication possible de ce resultat. [Traduit par la Redaction], 1. Introduction As a material for thin-film photovoltaic solar cell device applications, hydrogenated nanocrystalline silicon (nc-Si:H) offers a number of inherent advantages when contrasted with the case of hydrogenated amorphous [...]

We have synthesized silicon nanocrystalline structures from thermal annealing of thin film amorphous silicon-based multilayers. The annealing procedure that was carried out in vacuum at temperatures up to 1100°C is integrated in a X-ray diffraction (XRD) setup for real-time monitoring of the formation phases of the nanostructures. The microstructure of the crystallized films is investigated through experimental measurements combined with atomistic simulations of realistic nanocrystalline silicon (nc-Si) models. The multilayers consisting of uniformly alternating thicknesses of hydrogenated amorphous silicon and silicon oxide (Si[O.sub.2]) were deposited by plasma enhanced chemical vapor deposition on crystalline silicon and Corning glass substrates. The crystallized structure consisting of nc-Si structures embedded in an amorphous matrix were further characterized through XRD, Raman spectroscopy, and Fourier transform infrared measurements. We are able to show the different stages of nanostructure formation and how the sizes and the crystallized mass fraction can be controlled in our experimental synthesis. The crystallized silicon structures with large crystalline filling fractions exceeding 50% have been simulated with a robust classical molecular dynamics technique. The crystalline filling fractions and structural order of nc-Si obtained from this simulation are compared with our Raman and XRD measurements. PACS Nos.: 81.10Jt, 81.07.-b, 61.05.cp. Nous fabriquons des structures nanocristallines de silicium par recuit thermique de films minces multicouches de silicium amorphe. La procedure de recuit se fait dans une chambre a vide a temperature jusqu'a 1100°C, avec un appareillage in situ de diffraction X (XRD) pour surveiller en temps reel la formation des phases nanocristallines. Nous etudions la microstructure des films cristallises a l'aide de mesures experimentales et de simulations atomiques de modeles realistes de silicium nanocristallin (nc-Si). Les multicouches sont constitues de couches uniformes alternees de silicium amorphe hydrogene et d'oxyde de silicium Si[O.sub.2] et sont obtenus par depot chimique en phase vapeur avec traitement au plasma sur des substrats de silicium cristallin et de verre Corning. Les structures cristallisees sont des structures nc-Si incrustees dans une matrice amorphe et sont caracterisees par XRD, spectroscopie Raman et par mesures infra-rouge a transformee de Fourier. Nous sommes capables de montrer les differentes etapes de la formation de nanostructure et comment les grosseurs et les fractions massiques cristallisees peuvent etre controlees dans notre montage. Nous avons simule les structures cristallisees de silicium, avec des coefficients de remplissage de plus de 50%, a l'aide une solide technique de dynamique moleculaire classique. Nous comparons les fractions de remplissage et l'ordre structural de nc-Si obtenus dans cette simulation avec nos mesures Raman et XRD. [Traduit par la Redaction], 1. Introduction Silicon quantum dots (QDs) have great potential to be an absorber in solar cells, where the band gap can be tuned by the QD size. QDs have been [...]

Laser melt electrospinning is a novel technology to fabricate scaffolds in the tissue engineering applications. The melt electrospinning is much safer than the conventional solution electrospinning due to without solvent effect. In this study, thermoplastic polyurethane (TPU) micro/nanofibers were successfully prepared by using this method. The effects of laser current and applied voltage on the fibers morphologies were investigated by scanning electron microscopy. The thermal behaviors and crystallization conditions of the TPU under different states were demonstrated by differential scanning calorimetry and X-ray diffraction analysis. The mechanical property and the specific surface area of the TPU fibers membranes were also studied. All the analysis results showed that the effects of laser current and applied voltage on the average fiber diameter were complicated, the average fiber diameter ranging from 1.70 to 2.53 nm; the TPU is not an easily crystallized material; the electrospun fibers exhibited an amorphous phase; the average elongation at break laser of the electrospun TPU fiber membranes is about 134%; the average tensile strength is about 1.02 MPa and the specific surface area of the electrospun TPU fiber membrane is about 199 [m.sup.2]/g. POLYM. ENG. SCI., 54:1412-1417, 2014. © 2013 Society of Plastics Engineers, INTRODUCTION The polymer fibers have been applied in many areas such as high-performance filters, membranes optics, vascular grafts, protective clothing, molecular templates, tissue scaffolds, and sensing applications due to owning [...]

Amorphous phase dynamics in Poly(lactic acid) (PLA) with different crystallinity degrees have been investigated from the vitreous state to the glass transition by means of two calorimetric methods. Temperature Modulated Differential Scanning Calorimetry was used to characterize the heat capacity signals and the average cooperativity length at the glass transition in non-aged materials. Standard DSC was used to study the physical aging. It is shown that amorphous and fully crystallized PLA exhibit different relaxation parameters. For semicrystalline PLA with an intermediate degree of crystallinity, the peaks of the enthalpy of recovery and the out-of-phase heat capacity component are bimodal. The bimodality of the peaks is attributed to the relaxations of the inter-spherulitic and intraspherulitic amorphous phases, respectively. Thus, in partially crystallized PLA, the non-crystalline fraction of the material could be divided in three fractions, namely the Rigid Amorphous Fraction, the interspherulitic Mobile Amorphous Phase (MAP), and the intra-spherulitic MAP. Each of them exhibits a distinct molecular mobility. POLYM. ENG. SCI., 54:1144-1150, 2014., INTRODUCTION In recent years, environmental concerns have increased the interest in biodegradable and/or biosourced packaging materials to replace commonly used plastics issued from petrochemistry [1]. Nevertheless, using these kinds of [...]

ABSTRACT Nylon-6/epoxy resin composite with multiphase morphology has been successfully prepared via polymerization of caprolactam in N-methylpyrroli-done using N-acetyl caprolactam as the initiator. This was followed by reactive blending of [...]

Melt rheology and crystallization behavior of polyamide 6 (PA 6) and microcrystalline cellulose {MCC) composites were systematically studied in this research. The incorporation of MCC into the PA 6 matrix [...]

A semicrystalline poly(lactic acid) (PLA) was modified with the help of an epoxy-based chain extender (CE) during reactive extrusion. Different amounts of CE were used resulting in samples with increased and broadened molar mass distributions as revealed by size exclusion chromatography. Thermal properties were then investigated using differential scanning calorimetry (DSC) and polarized optical microscopy (POM). On one hand, the thermal ramps performed with DSC revealed that the glass transition was not modified by the chain extension process. On the other hand, the crystallization behavior was found to be highly impacted by this molecular modification. Decreases in the cold crystallization temperatures [T.sub.cc] and in the melting temperatures [T.sup.m] occurred when the CE content was raised. Isothermal crystallizations from the melt were performed using both DSC and POM. It revealed that the overall crystallization process was significantly faster for the chain-extended PLAs while crystalline ratios were lowered. An improvement of the nucleation process coupled with a reduced crystal growth was assumed to be responsible for this change. POLYM. ENG. SCI., 54:616-625, 2014. © 2013 Society of Plastics Engineers, INTRODUCTION Poly (lactic acid) (PLA) is a promising polymer as a biobased and biodggradable material. Current ecological concerns have confronted the plastic industry with the issue of sustainable production. Ideally, [...]

The processes involved in the formation and storage of magma within the Earth's upper crust are of fundamental importance to volcanology. Many volcanic eruptions, including some of the largest, result from the eruption of components stored for tens to hundreds of thousands of years before eruption (1-3). Although the physical conditions of magma storage and remobilization are of paramount importance for understanding volcanic processes, they remain relatively poorly known (4,5). Eruptions of crystal-rich magma are often suggested to require the mobilization of magma stored at near-solidus conditions (6-8); however, accumulation of significant eruptible magma volumes has also been argued to require extended storage of magma at higher temperatures (7-9). What has been lacking in this debate is clear observational evidence linking the thermal (and therefore physical) conditions within a magma reservoir to timescales of storage--that is, thermal histories. Here we present a method of constraining such thermal histories by combining timescales derived from uranium-series disequilibria, crystal sizes and trace-element zoning in crystals. At Mount Hood (Oregon, USA), only a small fraction of the total magma storage duration (at most 12 percent and probably much less than 1 per cent) has been spent at temperatures above the critical crystallinity (40-50 per cent) at which magma is easily mobilized. Partial data sets for other volcanoes also suggest that similar conditions of magma storage are widespread and therefore that rapid mobilization of magmas stored at near-solidus temperatures is common. Magma storage at low temperatures indicates that, although thermobarometry calculations based on mineral compositions may record the conditions of crystallization, they are unlikely to reflect the conditions of most of the time that the magma is stored. Our results also suggest that largely liquid magma bodies that can be imaged geophysically will be ephemeral features and therefore their detection could indicate imminent eruption., The thermal histories of magma bodies stored within the Earth's crust exert an important influence over the processes that lead to volcanic eruptions, but are poorly constrained by current observational [...]