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George D. Wignall - One of the best experts on this subject based on the ideXlab platform.
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Small-Angle Scattering Investigations of Poly(.epsilon.-caprolactone)/Polycarbonate Blends. 2. Small-Angle X-ray and Light Scattering Study of Semicrystalline/Semicrystalline and Semicrystalline/Amorphous Blend Morphologies
Macromolecules, 1994Co-Authors: Y. Wilson Cheung, Richard S. Stein, J. S. Lin, George D. WignallAbstract:Crystalline morphologies of poly(e-caprolactone) (PCL) and polycarbonate (PC) blends were probed with SAXS and SALS. Quantitative SAXS analysis suggested that random mixing of PCL and PC lamellae occurred in the Semicrystalline/Semicrystalline State. Two distinct regions of incorporation were identified in the Semicrystalline/amorphous State. It was found that PCL was rejected from the PC interlamellar region in the PCL-rich blends. In contrast, PCL was incorporated into the amorphous phase between the crystalline lamellae in the PC-rich
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Small-Angle Scattering Investigations of Crystalline Blend Morphologies of Poly(ε-Caprolactone) (PCL)/Polycarbonate (PC) Blends
MRS Online Proceedings Library, 1993Co-Authors: Y. Wilson Cheung, Richard S. Stein, George D. Wignall, J. S. LinAbstract:Crystalline morphologies of poly(ε-caprolactone) (PCL) and deuterated polycarbonate (PC) blends in both the Semicrystalline/amorphous State and Semicrystalline/Semicrystalline State were probed by small-angle neutron and X-ray scattering (SANS and SAXS). Due to the different contrast between the phases for neutrons and X-rays, SANS exhibited a monotonic drop in intensity with increasing scattering angle while SAXS showed lamellar (peak) scattering. Crystal- and amorphous-phase thickness were determined from the correlation function calculated from SAXS. This correlation function analysis suggested a transition from interlamellar exclusion to interlamellar incorporation of amorphous PCL in the PC lamellae. A two-correlation length model provided an excellent fit for the SANS data over the entire composition range. This model not only reproduced the shape but also the absolute magnitude of the scattering profiles. The long range correlation length (~10^2 Å) and the short range correlation length (~ 10 Å) derived from this model were inferred to be associated with the crystalline PC domains and the local clusters found in the amorphous phase, respectively.
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Small-Angle Scattering Investigations of Crystalline Blend Morphologies of Poly (E-Caprolactone) (PCL)/Polycarbonate (PC) Blends
MRS Proceedings, 1993Co-Authors: Y. Wilson Cheung, Richard S. Stein, George D. Wignall, J. S. LinAbstract:ABSTRACTCrystalline Morphologies of poly (e-caprolactone) (PCL) and deuterated polycarbonate (PC) blends in both the Semicrystalline/amorphous State and Semicrystalline/Semicrystalline State were probed by small-angle neutron and X-ray scattering (SANS and SAXS). Due to the different contrast between the phases for neutrons and X-rays, SANS exhibited a monotonie drop in intensity with increasing scattering angle while SAXS showed lamellar (peak) scattering.Crystal- and amorphous-phase thickness were determined from the correlation function calculated from SAXS. This correlation function analysis suggested a transition from interlamellar exclusion to interlamellar incorporation of amorphous PCL in the PC lamellae. A two-correlation length model provided an excellent fit for the SANS data over the entire composition range. This Model not only reproduced the shape but also the absolute magnitude of the scattering profiles. The long range correlation length (∼102 Å) and the short range correlation length (∼ 10 Å) derived from this model were inferred to be associated with the crystalline PC domains and the local clusters found in the amorphous phase, respectively.
Mariana Dana Damaceanu - One of the best experts on this subject based on the ideXlab platform.
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Tuning of the color of the emitted light from new polyperyleneimides containing oxadiazole and siloxane moieties
Dyes and Pigments, 2013Co-Authors: Mariana Dana Damaceanu, Maria Bruma, Catalin-paul Constantin, Mariana PintealaAbstract:Abstract Four new aromatic poly(peryleneimides) containing electron-withdrawing oxadiazole rings and flexible tetramethyldisiloxane units in the backbone were prepared by a one step polycondensation reaction at high temperature of four aromatic diamines containing preformed oxadiazole units with a mixture, in different ratios, of perylenetetracarboxylic dianhydride and tetramethyldisiloxane-1,3-bis(4-phthalic anhydride). The structure of these polymers was confirmed by FT-IR and 1 H NMR spectroscopy. The solubility, thermal stability and glass transition temperature of the poly(peryleneimides) were measured and discussed in correlation with their chemical structure. The solid polymers were studied by X-ray diffraction which revealed a Semicrystalline State consisting in face-to-face arranged columns of perylenediimide units for two of the polymers. The film-forming ability and the morphology of the resulting thin films were investigated using scanning electron microscopy which showed that two of the polymer films were organized into self-assembled rod-like structures. An extensive study of the photo-optical properties of these polymers highlighted the ability of the color of the emitted light to be modulated as a function of the excitation wavelengths, as was surveyed in the chromaticity diagrams. The Forster excitation energy transfer phenomenon from oxadiazole to perylenediimide chromophores was observed to occur for some of the polymers, for which the oxygen bridge appears to be responsible. In solution, high fluorescence quantum yields were obtained, up to 24%, while, in the solid State, low fluorescence emission was attained due to aggregation. These poly(peryleneimides) could be considered as promising candidates for high-performance materials to be used in novel optoelectronic applications, e.g. chemiluminescent sensors.
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Fluorescence behavior of Semicrystalline functionalized maleic acid copolymers containing 1,3,4-oxadiazole side chains
Polymer, 2012Co-Authors: Mariana Dana Damaceanu, Maria Bruma, Burkhard SchulzAbstract:The fluorescence behavior in solution and in solid State of functionalized copolymers based on poly(styrene-co-maleic acid) and poly(N-vinylpyrrolidone-co-maleic acid) containing 1,3,4-oxadiazole side chains was studied showing the UV- and blue light-emitting ability of these polymers. For the first time, maleic acid copolymer derivatives were synthesized by using Yamazaki–Higashi reaction. The polymers have a substitution degree in the range of 21–43.3% and are fully characterized in terms of chemical structure by 1H NMR, FTIR and UV–Vis spectroscopy, and by molecular weight measurements. The thermal stability and glass transition temperatures of the modified polymers were measured and compared with those of the raw polymeric support. The solid polymers were studied by X-ray diffraction which revealed a Semicrystalline State. Different morphologies, e.g. porous or spherulite-like were found in the very thin films prepared from these new copolymers when investigated by atomic force microscopy and polarized light microscopy. The influence of the morphology and crystallinity of the thin copolymer films on their fluorescence behavior was studied.
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Designing thermotropic liquid crystalline polyazomethines based on fluorene and/or oxadiazole chromophores
European Polymer Journal, 2011Co-Authors: Luminita Marin, Elena Perju, Mariana Dana DamaceanuAbstract:The main objective of this paper was to synthesize luminescent thermotropic liquid crystalline polyazomethines containing chromophoric mesogen, which design has been addressed to optoelectronic materials. The investigation of the thermotropic behavior by three complementary methods of analyses, i.e. polarized optical microscopy, differential scanning calorimetry and wide angle X-ray diffraction, indicated a nematic mesophase for the polymers containing oxadiazole units, either alternating or random ones. A mesomorphic State maintaining the degree of order of the Semicrystalline State while being viscous fluid was evidenced too. The photoluminescence spectra recorded for both polymer solutions and films exhibited a blue light emission. These results point to the possibility of obtaining monodomain or multidomain ordered thin films without grain boundaries showing good mechanical and luminescent properties.
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Copoly(peryleneimide)s Containing 1,3,4-Oxadiazole Rings: Synthesis and Properties
Journal of Polymer Science Part A: Polymer Chemistry, 2010Co-Authors: Radu-dan Rusu, Luminita Marin, Mariana Dana Damaceanu, Maria BrumaAbstract:New copolyimides containing perylenediimide, oxadiazole and hexafluoroisopropylidene moieties were prepared by one-step polycondensation reaction in solution at high temperature of aromatic diamines containing preformed oxadiazole ring with a mixture of a dianhydride having a perylene ring and another dianhydride with hexafluoroisopropylidene unit. The thermal stability and glass transition temperatures of these copolyimides were measured and compared with those of related polyimides. The solid polymers were also studied by polarized light microscopy and X-ray diffraction which revealed a Semicrystalline State consisting of face-to-face arranged columns of perylenediimide units. The film-forming ability and properties of the resulting thin films were investigated by using atom force microscopy and scanning electron microscopy which showed that the films were organized into self-assembled rod-like structures. The UV-Vis and photoluminescence properties in solution and in solid State were also investigated. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 4230–4242, 2010
Yongfeng Men - One of the best experts on this subject based on the ideXlab platform.
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Crystallization, recrystallization, and melting lines in syndiotactic polypropylene crystallized from quiescent melt and Semicrystalline State due to stress-induced localized melting and recrystallization.
The journal of physical chemistry. B, 2014Co-Authors: Yaotao Wang, Zhiyong Jiang, Yongfeng MenAbstract:Crystalline lamellar thickness in syndiotactic polypropylene (sPP) during crystallization from either isothermal molten or stretching induced localized melt States and during subsequent heating was investigated by means of temperature dependent small-angle X-ray scattering techniques. Well-defined crystallization lines where the reciprocal lamellar thickness is linearly dependent on crystallization temperature were observed. Unlike in the case of polybutene-1 where stretching crystallization line was shifted to direction of much smaller lamellar thickness (Macromolecules 2013, 46, 7874), the stretching induced crystallization line for sPP deviates from its corresponding isothermal crystallization line only slightly. Such phenomenon could be attributed to the fact that both crystallization processes from quiescent melt and stress induced localized melt are mediated in a mesomorphic phase in sPP. Subsequent heating of sPP after crystallization revealed the same melting behavior in both systems for the two kinds of crystallites obtained from either quiescent melt or stretching induced localized melt. Both of them underwent melting and recrystallization when the lamellar thickness was smaller than a critical value and melting directly without changing in thickness when the lamellar thickness was larger than the critical value. The melting behavior in sPP systems can be understood by considering the chain relaxation ability within crystalline phase and also can be used as evidence that the crystallization from molten State and stress-induced crystallization passed through the intermediate phase before forming crystallites.
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CRYSTALLIZATION KINETICS OF SYNDIOTACTIC POLYPROPYLENE STUDIED BY TIME-DEPENDENT LIGHT ATTENUATION
Chinese Journal of Polymer Science, 2008Co-Authors: Huiying Wen, Shichun Jiang, Yongfeng MenAbstract:Crystallization kinetics of syndiotactic polypropylene ( sPP) was observed by light attenuation measurements. The initial stages of temperature dependent sPP crystallization fall in the range of Rayleigh scattering and Rayleigh-Debye- Gans scattering. Initial time and growth time of crystallization were obtained, and the trend of crystallization temperature dependent linear attenuation coefficient on the radius and the index of the refraction of the spherulite were evaluated. of polymer crystallization are usually carried out by differential scanning calorimetry or X-ray scattering in the wide- and small-angle range, sometimes also by light scattering, dilatometry or time dependent vibrational spectroscopy. Although based on different properties there is not much difference in the sensitivity of all these methods. Reliable data are only obtained from values of the crystallinity in the range of some percent of the final values. This means that for growing spherulites, which usually reach end sizes in the order of several micrometers, measurements start only at sizes of several hundred nanometers. This, however, is already far away from the initial stages. Nuclei have sizes in the order of several to ten nanometers and these, together with the small hedrites and spherulites existing at the beginning, cannot be observed. To study the objects in these initial stages, one can now use atomic force microscopy (AFM), but this technique has also some shortcomings. Observations by AFM principally refer to the development and growth of spherulites at the free surface of a melt, and conditions here may differ from those in the bulk. In addition, deriving global properties from observations of the development of single objects is sometimes difficult, because a certain selectivity is usually involved. Presently, the work on polymer crystallization has given considerable attention to the possibility that the crystal phase in the final Semicrystalline State could be preceded by a transient liquid phase with density different from that of the initial quenched bulk isotropic melt or annealed glassy State. A number of papers have explicitly criticized the spinodal hypothesis and associated experimental studies, favoring the traditional picture of nucleation and growth. Various studies have suggested that the denser transient phase involves chain orientation, and there are good reasons to assume a crystal nucleation and growth which include an intermediate phase in the form of a coverage of the whole volume by a prior mesomorphic phase developing by a mechanism which resembles a spinodal process (7) , or a nucleation into a mesomorphic phase (8) , or the existence of a
J. S. Lin - One of the best experts on this subject based on the ideXlab platform.
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Small-Angle Scattering Investigations of Poly(.epsilon.-caprolactone)/Polycarbonate Blends. 2. Small-Angle X-ray and Light Scattering Study of Semicrystalline/Semicrystalline and Semicrystalline/Amorphous Blend Morphologies
Macromolecules, 1994Co-Authors: Y. Wilson Cheung, Richard S. Stein, J. S. Lin, George D. WignallAbstract:Crystalline morphologies of poly(e-caprolactone) (PCL) and polycarbonate (PC) blends were probed with SAXS and SALS. Quantitative SAXS analysis suggested that random mixing of PCL and PC lamellae occurred in the Semicrystalline/Semicrystalline State. Two distinct regions of incorporation were identified in the Semicrystalline/amorphous State. It was found that PCL was rejected from the PC interlamellar region in the PCL-rich blends. In contrast, PCL was incorporated into the amorphous phase between the crystalline lamellae in the PC-rich
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Small-Angle Scattering Investigations of Crystalline Blend Morphologies of Poly(ε-Caprolactone) (PCL)/Polycarbonate (PC) Blends
MRS Online Proceedings Library, 1993Co-Authors: Y. Wilson Cheung, Richard S. Stein, George D. Wignall, J. S. LinAbstract:Crystalline morphologies of poly(ε-caprolactone) (PCL) and deuterated polycarbonate (PC) blends in both the Semicrystalline/amorphous State and Semicrystalline/Semicrystalline State were probed by small-angle neutron and X-ray scattering (SANS and SAXS). Due to the different contrast between the phases for neutrons and X-rays, SANS exhibited a monotonic drop in intensity with increasing scattering angle while SAXS showed lamellar (peak) scattering. Crystal- and amorphous-phase thickness were determined from the correlation function calculated from SAXS. This correlation function analysis suggested a transition from interlamellar exclusion to interlamellar incorporation of amorphous PCL in the PC lamellae. A two-correlation length model provided an excellent fit for the SANS data over the entire composition range. This model not only reproduced the shape but also the absolute magnitude of the scattering profiles. The long range correlation length (~10^2 Å) and the short range correlation length (~ 10 Å) derived from this model were inferred to be associated with the crystalline PC domains and the local clusters found in the amorphous phase, respectively.
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Small-Angle Scattering Investigations of Crystalline Blend Morphologies of Poly (E-Caprolactone) (PCL)/Polycarbonate (PC) Blends
MRS Proceedings, 1993Co-Authors: Y. Wilson Cheung, Richard S. Stein, George D. Wignall, J. S. LinAbstract:ABSTRACTCrystalline Morphologies of poly (e-caprolactone) (PCL) and deuterated polycarbonate (PC) blends in both the Semicrystalline/amorphous State and Semicrystalline/Semicrystalline State were probed by small-angle neutron and X-ray scattering (SANS and SAXS). Due to the different contrast between the phases for neutrons and X-rays, SANS exhibited a monotonie drop in intensity with increasing scattering angle while SAXS showed lamellar (peak) scattering.Crystal- and amorphous-phase thickness were determined from the correlation function calculated from SAXS. This correlation function analysis suggested a transition from interlamellar exclusion to interlamellar incorporation of amorphous PCL in the PC lamellae. A two-correlation length model provided an excellent fit for the SANS data over the entire composition range. This Model not only reproduced the shape but also the absolute magnitude of the scattering profiles. The long range correlation length (∼102 Å) and the short range correlation length (∼ 10 Å) derived from this model were inferred to be associated with the crystalline PC domains and the local clusters found in the amorphous phase, respectively.
Y. Wilson Cheung - One of the best experts on this subject based on the ideXlab platform.
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Small-Angle Scattering Investigations of Poly(.epsilon.-caprolactone)/Polycarbonate Blends. 2. Small-Angle X-ray and Light Scattering Study of Semicrystalline/Semicrystalline and Semicrystalline/Amorphous Blend Morphologies
Macromolecules, 1994Co-Authors: Y. Wilson Cheung, Richard S. Stein, J. S. Lin, George D. WignallAbstract:Crystalline morphologies of poly(e-caprolactone) (PCL) and polycarbonate (PC) blends were probed with SAXS and SALS. Quantitative SAXS analysis suggested that random mixing of PCL and PC lamellae occurred in the Semicrystalline/Semicrystalline State. Two distinct regions of incorporation were identified in the Semicrystalline/amorphous State. It was found that PCL was rejected from the PC interlamellar region in the PCL-rich blends. In contrast, PCL was incorporated into the amorphous phase between the crystalline lamellae in the PC-rich
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Small-Angle Scattering Investigations of Crystalline Blend Morphologies of Poly (E-Caprolactone) (PCL)/Polycarbonate (PC) Blends
MRS Proceedings, 1993Co-Authors: Y. Wilson Cheung, Richard S. Stein, George D. Wignall, J. S. LinAbstract:ABSTRACTCrystalline Morphologies of poly (e-caprolactone) (PCL) and deuterated polycarbonate (PC) blends in both the Semicrystalline/amorphous State and Semicrystalline/Semicrystalline State were probed by small-angle neutron and X-ray scattering (SANS and SAXS). Due to the different contrast between the phases for neutrons and X-rays, SANS exhibited a monotonie drop in intensity with increasing scattering angle while SAXS showed lamellar (peak) scattering.Crystal- and amorphous-phase thickness were determined from the correlation function calculated from SAXS. This correlation function analysis suggested a transition from interlamellar exclusion to interlamellar incorporation of amorphous PCL in the PC lamellae. A two-correlation length model provided an excellent fit for the SANS data over the entire composition range. This Model not only reproduced the shape but also the absolute magnitude of the scattering profiles. The long range correlation length (∼102 Å) and the short range correlation length (∼ 10 Å) derived from this model were inferred to be associated with the crystalline PC domains and the local clusters found in the amorphous phase, respectively.
