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Composition profiles develop around growing PVDF spherulites in a blend with PMMA. These profiles assume stationary courses after a certain crystallization time provided that the overall degree of crystallinity is not too high. The composition-dependent growth rate and the diffusion-controlled remove of the surplus PMMA from the spherulite surface are then in a stationary equilibrium. The internal structure of the spherulites will then be homogeneous, too. Upon isothermal crystallization of a PVDF/PMMA = 60/40 (wt %) blend at 160°C for at least 4 h, the spherulites internal degree of crystallinity xc as related to the PVDF fraction obeys the inequality 55 wt % ≤ xc ≤ 84 wt %. The overall PMMA content within the spherulites as averaged over its whole inside has been determined by IR microscopy. It amounts to about 15 wt %. In contrast, the PMMA content of the amorphous phase within the spherulites (averaged again over its whole inside) ranges between 28 and 52 wt %. This composition jumps at the spherulite surface to 52 wt %. From the slope of the composition profiles outside the spherulites that have a width of more than 50 μm, the effective chain diffusion coefficient in blends as averaged over both components can be calculated to amount to (250 ± 100) μm2h−1. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2923–2930, 1998 相似文献
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Lidija Tušek Simona Strnad Karin Stana-Kleinschek Volker Ribitsch Carsten Werner 《Macromolecular Symposia》2002,181(1):467-478
The surface morphologies of PA 6 resulting from the use of various processing methods were studied by tapping mode atomic force microscopy. Three PA 6 samples: (1) a thin film, spin coated on a silicon wafer, (2) a freestanding film, i.e. a foil and (3) a monofilament, show definite morphological differences revealing typical supramolecular structures. The thin film having thickness of app. 35 nm is a good example of the initial step of spherulite formation where the sheaf development is still prominent. In an area of 100 μm2 1-4 spherulites can be detected which are typical of crystallization from the solution. The annealing (vacuum, 195°C, 3.5h) causes additional crystallization, which leads to a radial coordination and enlargement of spherulites to app. 50% in diameter and up to 40% in height. The morphology of foil (thickness of 100 μm) can be interpreted as a system of spherulites formed from the melt, and a typical fibrillar structure is observed on the surface of monofilament. 相似文献
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Benzophenone‐containing, anhydride‐terminated hyperbranched poly(amic acid)s were end‐capped by ortho‐alkyl aniline in situ and then chemically imidized, yielding autophotosensitive hyperbranched polyimides. The polyimides were soluble in strong polar solvents, such as N‐methyl‐2‐pyrrolidone, N‐dimethylformamide, dimethylacetamide, and dimethyl sulfoxide. Thermogravimetric analysis revealed their excellent thermal stability, with a 5 wt % thermal loss temperature in the range of 527–548 °C and a10 wt % thermal loss temperature in the range of 562–583 °C. The strong absorption of the polyimide films in ultraviolet–visible spectra at 365 nm indicated that the hyperbranched polyimides were patternable. Highly resolved images with a line width of 6 μm were developed by ultraviolet exposure of the polymer films. A well‐defined image with lines as thin as 3 μm was also patterned, but the lines were rounded at the edges. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2026–2035, 2003 相似文献
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Jin Kon Kim Byoung‐Kee Kim Minsoo Park 《Journal of Polymer Science.Polymer Physics》2000,38(5):707-715
The effect of liquid–liquid phase separation (LLPS) on the crystallization behavior of poly(ethylene‐ran‐vinyl acetate) with a vinyl acetate content of 9.5 wt % (EVA‐H) in the critical composition of a 35/65 (wt/wt) EVA‐H/paraffin wax blend was investigated by small‐angle light and X‐ray scattering methods and rheometry. This blend exhibited an upper critical solution temperature (UCST) of 98°C, and an LLPS was observed between the UCST and the melting point of 88°C for the EVA‐H in the blend. As the duration time in the LLPS region increased before crystallization at 65°C, both the spherulite size and the crystallization rate of the EVA‐H increased, but the degree of the lamellar ordering in the spherulite and the degree of crystallinity of the EVA‐H in the blend decreased. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 707–715, 2000 相似文献
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Takayuki Ikehara Hideo Kurihara Toshiyuki Kataoka 《Journal of Polymer Science.Polymer Physics》2009,47(5):539-547
The effects of the lamellar growth direction, extinction rings, and spherulitic boundaries of poly(butylene succinate) (PBSU) on the spherulitic growth of poly(ethylene oxide) (PEO) were investigated in miscible blends of the two crystalline polymers. In the crystallization process from a homogeneous melt, PBSU first developed volume‐filling spherulites, and then PEO spherulites nucleated and grew inside the PBSU spherulites. The lamellar growth direction of PEO was identical with that of PBSU even when the PBSU content was about 5 wt %. PEO, which intrinsically does not exhibit banded spherulites, showed apparent extinction rings inside the banded spherulites of PBSU. The growth rate of a PEO spherulite, GPEO, was influenced not only by the blend composition and the crystallization temperature of PEO, but also by the growth direction with respect to PBSU lamellae, the boundaries of PBSU spherulites, and the crystallization temperature of PBSU, TPBSU. The value of GPEO first increased with decreasing TPBSU when a PEO spherulite grew inside a single PBSU spherulite. Then, GPEO decreased when TPBSU was further decreased and a PEO spherulite grew through many tiny PBSU spherulites. This behavior was discussed based on the aforementioned factors affecting GPEO. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 539–547, 2009 相似文献
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Yuxian An Lisong Dong Guang Li Zhishen Mo Zhiliu Feng 《Journal of Polymer Science.Polymer Physics》2000,38(14):1860-1867
The miscibility, spherulite growth kinetics, and morphology of binary blends of poly(β‐hydroxybutyrate) (PHB) and poly(methyl acrylate) (PMA) were studied with differential scanning calorimetry, optical microscopy, and small‐angle X‐ray scattering (SAXS). As the PMA content increases in the blends, the glass‐transition temperature and cold‐crystallization temperature increase, but the melting point decreases. The interaction parameter between PHB and PMA, obtained from an analysis of the equilibrium‐melting‐point depression, is −0.074. The presence of an amorphous PMA component results in a reduction in the rate of spherulite growth of PHB. The radial growth rates of spherulites were analyzed with the Lauritzen–Hoffman model. The spherulites of PHB were volume‐filled, indicating the inclusion of PMA within the spherulites. The long period obtained from SAXS increases with increased PMA content, implying that the amorphous PMA is entrapped in the interlamellar region of PHB during the crystallization process of PHB. All the results presented show that PHB and PMA are miscible in the melt. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1860–1867, 2000 相似文献
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Detailed analysis of temperature dependences of spherulite morphology and crystallite orientation of poly(vinylidene fluoride) via a combinatorial method 下载免费PDF全文
Temperature dependences of spherulite morphology and crystal orientation of poly(vinylidene fluoride) (PVDF) were systematically investigated via a combinatorial method. The method created a temperature gradient ranging from 130 to 200 °C. Results show that the preferential orientation of the crystallites changes with the crystallization temperature. The crystallization at 169 °C gives the most highly developed crystalline state of PVDF crystalline form II (α form), in which the spherulite size is maximal, and the crystallite sizes are also the longest, about 200 nm along the b axes. Besides, the a‐axis is almost parallel to the film normal. It indicates that the crystallization rate is the highest in the b‐axis direction. The perferential orientation at higher temperatures may be attributed to the confined 2D growth of the PVDF spherulites in the thin film, whereas the spherulites grow in the 3D mode at lower temperatures. The crystallization behavior revealed in the method is consistent with the results of melt isothermal crystallization experiments. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 253–261 相似文献
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Rhythmic growth of ring‐banded spherulites in blends of liquid crystalline methoxy‐poly(aryl ether ketone) (M‐PAEK) and poly(aryl ether ether ketone) (PEEK) has been investigated by means of differential scanning calorimetry (DSC), polarized light microscopy (PLM), and scanning electron microscopy (SEM) techniques. The measurements reveal that the formation of the rhythmically grown ring‐banded spherulites in the M‐PAEK/PEEK blends is strongly dependent on the blend composition. In the M‐PAEK‐rich blends, upon cooling, an unusual ring‐banded spherulite is formed, which is ascribed to structural discontinuity caused by a rhythmic radial growth. For the 50:50 M‐PAEK/PEEK blend, ring‐banded spherulites and individual PEEK spherulites coexist in the system. In the blends with PEEK as the predominant component, M‐PAEK is rejected into the boundary of PEEK spherulites. The cooling rate and crystallization temperature have great effect on the phase behavior, especially the ring‐banded spherulite formation in the blends. In addition, the effects of M‐PAEK phase transition rate and phase separation rate on banded spherulite formation is discussed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3011–3024, 2007 相似文献
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Chengwu Hua Zhimin Chen Qun Xu Linghao He 《Journal of Polymer Science.Polymer Physics》2009,47(8):784-792
The ring‐banded spherulites in poly(ε‐caprolactone) (PCL) solution‐casting films in the absence and presence of multi‐walled carbon nanotube (MWCNT) are studied by atomic force microscopy (AFM), polarized optical microscopy (POM), transmission electron microscopy (TEM), and scanning electronic microscopy (SEM). The results indicate that birefringent ring‐banded spherulites of PCL can grow from solution below 50 °C, and the temperature is much lower than that from pure PCL melt. We also find out that the presence of MWCNT apparently widen the temperature range of forming ring‐banded structure. Furthermore, the mechanism for the ring‐banded structure forming is studied, and it is attributed to the twisting of lamellae crystals, and the driving force is suggested including the deflexion of lamellae bundles. In addition, effect of compressed CO2 on the morphology of PCL and PCL/MWCNT solution‐casting film is also investigated, and the results reveal that both PCL and PCL/MWCNT films undergo recrystallization with the treatment of compressed CO2 and accordingly, the related properties can be adjusted. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 784–792, 2009 相似文献
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Gregory P. Moriarty Sukanta De Paul J. King Umar Khan Michael Via Julia A. King Jonathan N. Coleman Jaime C. Grunlan 《Journal of Polymer Science.Polymer Physics》2013,51(2):119-123
Organic thin film nanocomposites, prepared by liquid‐phase exfoliation, were investigated for their superior electrical properties and thermoelectric behavior. Single‐walled carbon nanotubes (SWNT) were stabilized by intrinsically conductive poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) in an aqueous solution. The electrical conductivity (σ) was found to increase linearly as 20 to 95 wt % SWNT. At 95 wt % SWNT, these thin films exhibit metallic electrical conductivity (~4.0 × 105 S m?1) that is among the highest values ever reported for a free‐standing, fully organic material. The thermopower (S) remains relatively unaltered as the electrical conductivity increases, leading to a maximum power factor (S2σ) of 140 μW m?1 K?2. This power factor is within an order of magnitude of bismuth telluride, so it is believed that these flexible films could be used for some unique thermoelectric applications requiring mechanical flexibility and printability. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013 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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Zhibo Li Dezhu Ma Xiaomin Cheng Xiaolie Luo Guoying Zhang 《Journal of Polymer Science.Polymer Physics》2001,39(6):634-644
The crystallization behaviors and spherulite morphology of a series of butylene terephthalate–ϵ‐caprolactone (BCL) copolyesters were explored with differential scanning calorimetry, polarized light microscopy, and wide‐angle X‐ray diffraction. The crystallization characteristics reflecting the segmented properties of BCL copolyesters are discussed. For BCL copolyesters with low or high hard‐segment contents, the ϵ‐caprolactone segments or butylene terephthalate segments are long enough to crystallize and even grow spherulites under appropriate conditions, and the crystallizability strengthens with increases in the corresponding segment sequence length. In BCL copolyesters, the crystallization of the soft segments requires a considerably long sequence length, whereas the hard segments even containing only one structural unit can still crystallize and even grow spherulites. The hard segments can grow the usual spherulites at a higher temperature like the poly(butylene terephthalate) homopolymer. The crystallizabilities of hard segments and soft segments for BCL and ethylene terephthalate–ϵ‐caprolactone copolyesters are compared and discussed. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 634–644, 2001 相似文献
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Jun Xu Bao‐Hua Guo Guo‐Qiang Chen Zeng‐Min Zhang 《Journal of Polymer Science.Polymer Physics》2003,41(18):2128-2134
On banded spherulites of poly(3‐hydroxybutyrate) and its copolymers, fine circles were observed between either cross‐polarizers or without polarizers. Atomic force microscopy was applied to confirm that these circles are terraces with heights up to several hundred nanometers rather than cracks. Real‐time observation demonstrated that the terrace forms at the front of the growing spherulites just before or exactly when two spherulites impinge on each other. Terraces were observed on the spherulites crystallized from melt confined between glass or polyimide slides rather than poly(ethylene terephthalate) slides. The formation of the terraces may have resulted from instability of the moving boundary of the melt film confined between the spherulite surface and cover slide. Wettability of the substrate played an important role in the formation of the terraces. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2128–2134, 2003 相似文献
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Xikui Liu Jialing Tang Yuanyuan Zheng Yi Gu 《Journal of Polymer Science.Polymer Physics》2005,43(15):1997-2004
The crystalline morphology and structural development of aromatic polyimides during an optimum continuous thermal imidization procedure were examined by means of polarized optical microscopy and X‐ray diffraction. During thermal imidization, 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride/1,3‐diaminobenzene polyimide samples formed complicated spherulites, which, in addition to zigzag Maltese crosses, also showed concentric extinction rings, which are characteristic of banded spherulites. The factors affecting the formation of banded spherulites were studied. The initial imidization conditions dramatically affected the formation of the banded spherulite morphology: slow heating (0.5 °C/min) or fast heating (20 °C/min) led to relatively small polyimide spherulites and less identifiable extinction rings. The morphological features were also affected by the molecular weight of the polyimide: higher molecular weight samples showed typical banded spherulites, whereas low‐molecular‐weight samples formed degenerated banded spherulites. In all the spherulites formed in 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride/1,3‐diaminobenzene polyimides, special zigzag Maltese crosses, instead of normal Maltese crosses, were observed. The relationship between the imidization procedure and the spherulite morphology formation was also studied. X‐ray and Fourier transform infrared together revealed that after several minutes of thermal treatment, the crystallization was nearly complete, with a 42.5% degree of crystallinity; meanwhile, only some poly(amic acid) converted to the corresponding polyimide, with a 27% degree of imidization. The crystalline morphology and structure formed in the initial stage of the imidization process were maintained during the following imidization processing at an elevated temperature. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1997–2004, 2005 相似文献
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Yong He Tong Wu Jia Wei Zhongyong Fan Suming Li 《Journal of Polymer Science.Polymer Physics》2008,46(10):959-970
Polylactide (PLA) homo‐ and stereocopolymers containing 100, 98, 96, 94, and 92% L ‐lactyl units, respectively, were synthesized by ring opening polymerization of L ‐lactide and DL ‐Lactide, using zinc lactate as catalyst. Differential scanning calorimetric analysis measurements show that incorporation of D ‐lactyl units leads to decrease of the crystallization rate of the copolymers. However, the crystallization mechanism and the amount of crystallizable fraction are not affected. The enzymatic degradation was performed at 37 °C in a pH 8.6 Tris buffer containing proteinase K. Two distinct morphologies were obtained by melt crystallization for PLA films with ca. 80 μm of thickness. It is confirmed that proteinase K can degrade both the free and confined amorphous regions. Lamella stacks in spherulites retain their orientation during enzymatic degradation. PLA crystal morphologies are affected by the content of D ‐lactyl units. Factors such as the nucleus location and the D ‐lactyl units' exclusion as amorphous fraction were considered to elucidate the observed PLA spherulite morphologies. Infrared spectroscopy and mass loss measurements were also combined to better understand the degradation behaviors. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 959–970, 2008 相似文献
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Hyo‐Sik Min Dong‐Wan Kang Doo‐Yeon Lee Dong‐Won Kim 《Journal of Polymer Science.Polymer Physics》2002,40(14):1496-1502
Porous membranes based on acrylonitrile/methyl methacrylate copolymer were prepared by a phase‐inversion method. Microstructures of the porous membranes were controlled through the variation of the evaporation drying time before immersion in a nonsolvent bath. Gel polymer electrolytes were prepared from these porous membranes via soaking in an organic electrolyte solution. They encapsulated the electrolyte solution well without solvent leakage and maintained good mechanical properties that allowed the preparation of thin films (~23 μm). These systems showed acceptable ionic conductivity values (>6.0 × 10?4 S/cm) at room temperature and sufficient electrochemical stability over 4.4 V that allowed applications in lithium‐ion polymer batteries. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1496–1502, 2002 相似文献
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Upon crystalline solidification of one component in a homogeneously molten polymer blend, composition profiles develop outside (i.e., in the rest melt) and behind (i.e., within the spherulites) the crystal growth front. The present article is devoted to the detailed verification and the interpretation of these distributions and their temporal development inside growing spherulites. To this end, the energy dispersive X‐ray emission (EDX) of suitable elements has been recorded locally resolved in a scanning electron microscope and evaluated correspondingly. The investigations were performed at the melt homogeneous blend of poly(vinylidene fluoride) (PVDF) as crystallizing and poly(methyl methacrylate) (PMMA) as steadily amorphous component. If the spherulites are not volume filling, the mean PMMA content 〈?PMMA〉 inside the PVDF spherulites is for all blends about 0.2 below the starting composition. ?PMMA increases however slightly from the center of a spherulite to its border. That increase reflects the PMMA concentration in front of the spherulite surface, which increases likewise with time, and is clearly above the initial composition. There is at the spherulite surface, consequently, a remarkable jump in composition from the spherulite internal to its amorphous surroundings. It may amount up to 0.5. With volume filling spherulites, a slight variation of the composition from the center of a spherulite to its border is observed, too. This proves that also at these conditions composition profiles develop in the spherulite's surroundings. They remain however so weak that they do not inhibit crystallization even in its later stages. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 338–346, 2006 相似文献
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R. Wellscheid J. Wüst B.-J. Jungnickel 《Journal of Polymer Science.Polymer Physics》1996,34(5):893-900
It is well known that crystallization of one component in a polymer blend causes composition profiles around the growing spherulites. Amplitude and width of these profiles, respectively, depend on the ratio between the rates of diffusion and of spherulite growth. They can be determined by suitable experimental means. In the present article, the profiles are modeled, starting from Frank's solution of the diffusion equation in spherical coordinates under the boundary condition of moving walls that simultaneously are sources of the diffusing material. Modeled and experimentally determined profiles in PVDF/PEA and PCL/PS blends agree well. The analysis yields estimates for the diffusion coefficient D in polymeric melts as D ≅ (50 ··· 500) μm2/h. Finally, the interference of the composition profiles around several adjacent spherulites can be demonstrated. © 1996 John Wiley & Sons, Inc. 相似文献