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1.
Emma Botines Lourdes Franco Alfonso Rodríguez‐Galn Jordi Puiggalí 《Journal of Polymer Science.Polymer Physics》2003,41(9):903-912
Isothermal crystallization kinetics of a new sequential poly(ester amide) derived from glycine, 1,4‐butanediol, and adipic acid was investigated with differential scanning calorimetry and optical microscopy. The Avrami analysis was performed to obtain the kinetic parameters of primary and secondary crystallization. The experimental data indicate a heterogeneous nucleation with spherical growth geometry for the primary crystallization, whereas a linear growth within formed spherulites is characteristic of the last crystallization stages. The Lauritzen–Hoffman analysis was also undertaken to determine the different crystallization regimes, having estimated the corresponding nucleation constants. Temperature dependence of the normalized crystallization‐rate constants was tested with different theoretical equations. These allow an estimation of a temperature close to 90 °C for the maximum crystallization rate. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 903–912, 2003 相似文献
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Haopeng Wang Jong K. Keum Anne Hiltner Eric Baer 《Macromolecular rapid communications》2010,31(4):356-361
Using a layer‐multiplying coextrusion process to fabricate films with thousands of alternating polymer nanolayers, we report here a new crystalline morphology in confined polymer nanolayers and an abrupt transition in the crystallization habit. At higher temperatures, poly(ethylene oxide) crystallizes as large, in‐plane lamellae. A 5 °C change in the crystallization temperature produces an on‐edge lamellar orientation. The results point to a transition from heterogeneous nucleation to substrate‐assisted nucleation. This may be a general phenomenon that accounts for previously unexplained differences in the preferred chain alignment of confined polymer crystals.
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J. Weng R. H. Olley D. C. Bassett P. Jskelinen 《Journal of Polymer Science.Polymer Physics》2004,42(18):3318-3332
Of the three melting peaks typical of a propylene–ethylene random copolymer (with 5.1 wt % ethylene) crystallized between 110 and 140 °C, the two higher peaks result from primary and secondary isothermal crystallization, whereas the material crystallized on cooling gives the lowest peak. In contrast to polypropylene homopolymers, which show strong morphological changes developing from the center of a spherulite, copolymer specimens are uniformly crosshatched. The highest melting peak is related to an open crosshatched framework of primary lamellae, and the next lower peak is related to later forming subsidiary lamellae filling the intervening space. The origin and nature of these double peaks are discussed in terms of the fractional crystallization and the ensuing constraints placed on isothermal lamellar thickening as a result of the exclusion of the comonomer from the polypropylene lattice. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3318–3332, 2004 相似文献
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Deepak S. Langhe Jong K. Keum Eric Baer 《Journal of Polymer Science.Polymer Physics》2011,49(2):159-171
A layer multiplying coextrusion process was used to produce multilayered polypropylene/polystyrene (PP/PS) films with various nucleating agents. When heated into the melt, the thin PP layers broke up into submicron PP droplets that exhibited fractionated crystallization. If the initial PP layers were 20 nm or less, the resulting droplets exhibited exclusively homogeneous nucleation. If a nucleating agent was added, the systematic departure from homogeneous nucleation provided insight into the nature of the heterogeneous nucleation. In this study, we used thermal analysis, atomic force microscopy (AFM), and wide angle X‐Ray scattering (WAXS) to examine the effect of two nucleating agents. We confirmed with WAXS and AFM that a soluble sorbitol nucleating agent for the PP α‐form operates in three concentration regimes as proposed in a previous study. Morphologically, homogeneous nucleation of the submicron droplets produced a granular texture. The correlation length from small‐angle X‐Ray scattering (SAXS) suggested that the grains contained 1–3 mesophase domains. Drawing on classical nucleation theory, the critical size nucleus of an individual mesophase domain was estimated to be about 2 nm3, which was considerably smaller than the mesophase domain. This pointed to mesophase crystallization that included the processes of nucleation and growth. Additional experiments were performed with nucleating agents for the PP β‐form. However, they were not effective in nucleating crystallization of the droplets, presumably because they were essentially insoluble in PP and the nucleating particles were too large to be accommodated in the PP droplets. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011 相似文献
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The atomic force microscope (AFM) has been used to investigate morphological development during the crystallization of poly(ethylene oxide) (PEO) from the melt. PEOs with molecular weights of 1 × 105 and 7 × 106 were used. Height and amplitude images were recorded, using the tapping mode. For both polymers, the mode of spherulite development varied with the velocity of the growth front. For slow growth velocities, the growth of the crystallites was linear, with growth initially occurring by single lamellae, later developing into growth arms by screw dislocation spawning of crystallites. At intermediate growth velocities, stacks of lamellae develop rapidly. The splaying apart of adjacent crystals and growth arms is abundant. The operation of growth spirals was observed directly in this growth velocity range. The crystals formed by the giant screw dislocations diverge immediately from the original growth direction, providing a source of interlamellar splaying. At low and intermediate velocities, the front propagates by the advance of primary growth arms, with the regions between the arms filled in by arms growing behind the primary front. At the highest velocity observed here, the formation of lamellar bundles and immediate splaying results in recognizable spherulites developing at the earliest stages of crystallization. The change from linear growth to splaying and nonlinear growth are qualitatively explained in terms of driving force, elastic resistance and the presence of compositional and/or elastic fields in the melt. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2311–2325, 1998 相似文献
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Y. Jin M. Rogunova A. Hiltner E. Baer R. Nowacki A. Galeski E. Piorkowska 《Journal of Polymer Science.Polymer Physics》2004,42(18):3380-3396
Films with a thousand alternating layers of isotactic polypropylene (PP) and polystyrene (PS) were prepared by layer‐multiplying coextrusion. The crystal structure of extremely thin PP layers confined between PS layers was studied by optical light microscopy (OM), atomic force microscopy (AFM), differential scanning calorimetry (DSC), small‐angle X‐ray scattering (SAXS), and wide‐angle X‐ray scattering (WAXS). Changes in structure were observed as the PP layer thickness decreased to the nanoscale. The thin PP discoids were largely composed of edge‐on lamellae with (040) planes lying flat on the interface. In layers 65 and 10‐nm thick, compressed d‐spacings in the directions perpendicular to the chains and loss of registry along the chain axis were suggestive of smectic packing of conformationally distorted chains. Even so, crystalline lamellae were distinguishable in the AFM images. In addition to the crystal population with (040) planes parallel to the interface, the WAXS from layers 65‐nm thick revealed another crystal fraction with (110) planes parallel to the interface and (040) planes perpendicular to the interface. This fraction was more evident in layers 10‐nm thick, where it accounted for approximately 10–20% of the crystallinity. Decreasing layer thickness resulted in a change of the crystal growth plane from the usual (110) to the more rare (010). The new crystal structure possibly served to fill‐in the radial structure of the dendritic discoids when a limitation to the thickness of the layer left only a little space for secondary nucleation of the crosshatched lamella. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3380–3396, 2004 相似文献
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Takayuki Ikehara Hironori Kimura Toshiyuki Kataoka 《Journal of Polymer Science.Polymer Physics》2010,48(6):706-711
Miscible blends of three crystalline polymers, namely poly(butylene succinate) (PBS), poly(ethylene succinate) (PES), and poly(oxyethylene) (POE), exhibited interpenetrating spherulites, where a spherulite of one component grows inside the spherulites of other components. PBS and PES were immiscible above the melting points, Tm, of these substances, while ternary blends with POE showed miscibility, which depended on the molecular weight of POE. PBS and PES exhibited the same spherulitic growth process as in a miscible binary blend when they were crystallized from a homogeneous ternary melt. Spherulites of PBS, which is the highest‐Tm component, filled the whole volume first when a miscible ternary blend was quenched below Tm of POE, the lowest‐Tm component. Then, the blends showed either two types of crystallization processes. One was successive nucleation and growth of PES and POE spherulites, that is, PES nucleated and developed spherulites inside the PBS spherulites and then POE spherulites grew inside the interlocked spherulites of PBS and PES. The other was simultaneous growth and the formation of interpenetrating spherulites of PES and POE inside the PBS spherulites. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 706–711, 2010 相似文献
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Layer‐multiplying coextrusion was used to fabricate assemblies of 257 layers, in which polypropylene (PP) nanolayers alternated with thicker polystyrene (PS) layers. The PP layer thickness was varied from 12 to 200 nm. When the assembly was heated into the melt, interfacial instability‐driven breakup of the thin PP layers produced a dispersion of PP particles in a PS matrix. Particle size analysis indicated that breakup of PP microlayers produced a bimodal particle size distribution. A population of submicron particles formed because of the Rayleigh instability, and a second population of large particles formed by relaxation. Breakup of 12‐nm layers resulted in primarily submicron particles. The fraction of PP as submicron particles dropped dramatically as the layer thickness increased to 40 nm. The particle dispersion was characterized by thermal analysis and wide angle X‐ray diffraction. Fractionated crystallization gave rise to four crystallization exotherms at 40, 60, 85, and 100 °C. The exotherm at 40 °C was identified with homogeneous nucleation of the submicron particles in the smectic form. Exotherms at higher temperatures represented fractionated crystallization of the large micron‐sized particles in the PP α‐form. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1138–1151, 2007 相似文献
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The high‐pressure crystallized bisphenol‐A polycarbonate/dioctyl phthalate (BAPC/DOP) blend samples were investigated using wide‐angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The specimens were prepared in a piston‐cylinder high‐pressure apparatus by varying the temperature, the pressure and the crystallization time for a BAPC/DOP (90/10, wt/wt) blend. The other four specimens were also prepared with different weight ratios of BAPC/DOP. The DSC results showed that the amorphous BAPC could be crystallized in 45 min by the blending with DOP and the subsequent high‐pressure treatment. A wide variety of morphologies of BAPC crystals were disclosed by SEM, including spherulites, spatial dendrites, crystalbars, platelets and regular polygonal crystals of different characteristics. The folded‐chain lamellar crystals were found to be the substructures of these observed BAPC microstructures. The SEM revealed a granular substructure of the lamellae in a low‐crystallinity sample as well, which indicated that the crystallization of BAPC in the multiphase system might possibly agree with the model developed by Strobl. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2715–2728, 2007 相似文献
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We investigated the crystallization growth of isotactic polypropylene under carbon dioxide (CO2) at various CO2 pressures and temperatures by in situ observation with a digital high‐fidelity microscope and a specially designed high‐pressure visualized cell. The fibrils within the spherulite were distorted and branched by crystallization under CO2 at pressures higher than 2 MPa, and this suggested the exclusion of CO2 from the growth front of the fibrils. The spherulite growth rate (G) at 140 °C increased with the CO2 pressure, attained a maximum value around 0.3 MPa, and then decreased. Above 6 MPa, it became slower than that under air at the ambient pressure. An analysis of the crystallization kinetics by the Hoffman–Lauritzen theory revealed that the pressure dependence of G could be ascribed to the change in the transportation rate of crystallizable molecules (βg) with pressure; that is, βg increased and then decreased with pressure. The increase in βg at a low pressure was caused by the plasticizing effect of CO2, whereas the decrease in βg at a high pressure was due to the exclusion of CO2 from the crystal growth front. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1565–1572, 2004 相似文献
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A. Schaper R. Hirte C. Ruscher R. Hillebrand E. Walenta 《Colloid and polymer science》1986,264(8):649-658
The application of phosphotungstic acid (PTA) as a staining agent with appropriate hardening procedures and accurate ultra-thin sectioning has enabled the direct transmission electron microscope (TEM) investigation to be carried out on the lamellar fine structure of bulk nylon 6. Details of the organization of the crystal lamellae within spherulites and other morphological structures, their shape and, especially, their dimensions were revealed and the mean structural long period was determined. Interspherulitic regions without any indication of crystalline ordering could be observed in samples which were rapidly cooled from the melt. The investigations on bulk material were completed by observations on solution-grown thin films. Optical diffraction (OD) was used for evaluating the electron micrographs; the results were compared with the data from small angle X-ray scattering (SAXS). 相似文献
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M. M. Shahin R. H. Olley M. J. Blissett 《Journal of Polymer Science.Polymer Physics》1999,37(16):2279-2286
Permanganic reagents, developed for revealing semicrystalline morphology in olefin polymers under the electron microscope, have been modified by changing the water content to give the best resolution of detail in different polyethylene specimens. An optimum reagent is chosen to characterize a special feature of polyethylene spherulites, namely the S‐profile of dominant lamellae seen as growing towards the observer. This reagent consists of 1% weight of potassium permanganate in a mixture of 10 volumes concentrated sulphuric acid, 4 volumes of 85% orthophosphoric acid, and 1 volume of water. This study is set in the historical context of banded spherulite studies. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2279–2286, 1999 相似文献
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BTDA/m‐PDA polyimide banded spherulites with different band spacing were observed in the same sandwiched film. Atom force microscopy (AFM) analysis suggested that the banded structure was caused by periodic twisting of radial grown lamella bundles. Based on polarizing light microscopy (PLM) and AFM observation, it was found that spherulites grown near the center of the film exhibited bigger band spacing and consisted of wider lamellae compared with those grown near the fringe, which was suggested to be caused by different solvent amount during imidization and crystallization: the more solvent existed, the wider the lamella would grow and the bigger the band spacing would be. It was further proved by changing the film thickness and PAA solution concentration. SEM observation showed that when crystallized in the solution, the lamella became ultra thick and straight, and formed small particles. Powder X‐ray diffraction revealed that crystal structures of the banded spherulite and the small particle were identical or at least very similar. Another solvent with lower boiling point was used in sample preparation, however, under the same preparation conditions, the grown features of banded spherulites did not change. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 659–667, 2008 相似文献
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Xiaoqing Liu Chuncheng Li Guohu Guan Xuepei Yuan Yaonan Xiao Dong Zhang 《Journal of Polymer Science.Polymer Physics》2005,43(19):2694-2704
The melting behavior, crystallization behavior, and morphology of PBSR, which is Poly(butylene succinate) modified with rosin maleopimaric acid anhydride (RMA), were investigated with differential scanning calorimetry (DSC) and polarized optical microscope (POM). The multiple endotherms were ascribed to the recrystallization during DSC measurement and the equilibrium melting temperature determined by the Peak L, which was associated with the fusion of the crystals grown by normal primary crystallization, was 125.9 °C. After the kinetic parameters for isothermal crystallization of PBSR were determined by Avrami equation, to make a detailed regime transition analysis, the well‐established Lauritzen–Hoffman equation was employed. The results indicated that there were two regimes, regime II and regime III, in the range of higher and lower crystallization temperature, respectively. The regime transition temperature is about 81 °C. At last, the spherulitic morphologies of PBSR after being crystallized isothermally at different temperature were observed with the help of POM. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2694–2704, 2005 相似文献
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Rachele Pucciariello Loredana Tammaro Vincenzo Villani Vittoria Vittoria 《Journal of Polymer Science.Polymer Physics》2007,45(8):945-954
Novel composites based on poly(ε‐caprolactone) (PCL) and an organically modified layer double hydroxide (LDH) obtained using the melt‐extrusion technique have been characterized through structural, thermal, and mechanical analyses. Although exfoliation has not been achieved and despite the very low content of filler (from 1 to 3% by weight), significant enhancements are obtained in the physical and mechanical properties of the composites with respect to neat PCL. As a consequence, LDHs can substitute other nanofillers, in particular, cationic clays for polymeric matrices. They can be modified by a large number of organic anions, generally more numerous than the cationic ones, and can be mixed in very simple ways with polymers. This makes such nanofillers suitable to obtain new hybrid materials for a series of applications, from active food packaging to intelligent materials for biomedical device, for example, controlled drug release. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 945–954, 2007 相似文献
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R. Wellscheid J. Wüst B.-J. Jungnickel 《Journal of Polymer Science.Polymer Physics》1996,34(2):267-275
In polymer blends of an amorphous and a semicrystalline component, the crystallization kinetics and the resulting morphology are heavily determined by the diffusion ability of the whole chains and by the dwelling site of the amorphous polymer. Depending on the relative rates of spherulite growth and chain diffusion, radial composition profiles around the growing spherulites and a gradual increase of the melt bulk composition can develop. The resulting change in composition, particularly at the crystallization front, causes a corresponding temporal variation of the spherulite growth rate. In the present article, two experimental techniques are introduced to prove the existence and to determine the course of these concentration profiles. They are based on the composition dependences of the spherulite growth rate and the number density of primary nuclei. Their efficiency is demonstrated by measurements on PVDF/PEA blends. The blend composition at the crystal growth front was found to change by absolute 25%, and the width of the profile can amount to up to 70 μm. © 1996 John Wiley & Sons, Inc. 相似文献
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