Molecular orientation and conductivity in highly oriented poly(p-phenylene vinylene)

Briers, J.; Eevers, Walter; Cos, Paul; Geise, H. J.; Mertens, R.; Nagels, P.; Zhang, X.B.; Tendeloo, Gustaaf Van; Herrebout, Wouter A.; Veken, B. Van der

doi:10.1016/0032-3861(94)90804-4

Cited by 15 publications

(19 citation statements)

References 10 publications

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“…Infrared dichroic ratio measurements of the main infrared-active modes in PPV films prepared with a draw ratio l ¼ 5 yielded values for the Hermans orientation function of 0.90 [13], 0.94 [15], and 0.96 [20]. Despite demonstrating the same general trends, however, the values for the Hermans orientation distribution function, as determined from infrared dichroic ratios, are lower than those obtained from X-ray measurements.…”

Section: Introductioncontrasting

confidence: 49%

“…Electron microscopy studies have confirmed a high degree of orientational order in highly stretched PPV films. In such films, the Hermans orientation function ranged from 0.94 to 0.99, and the maximum deviation between fibers and the direction of stretching was found to be approximately 98 [16,20,21].…”

Section: Introductionmentioning

confidence: 96%

“…The lateral packing of PPV polymer chains is very regular within individual PPV crystallites [14]. Electron diffraction studies have shown that PPV has a paracrystalline structure with a monoclinic unit cell [18,20,31]. Paracrystallinity describes systems that possess imperfect crystalline order [32], so that although the molecular chains exhibit high degrees of alignment along the stretch axis, they show significant axial translational disorder [18].…”

Section: Introductionmentioning

confidence: 98%

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Determination of Molecular Orientational Order in Cold-Stretched Poly(p-phenylene vinylene) Thin Films by DECODER 13C NMR

Kropewnicki

Schaefer

Hehn

et al. 2002

Solid State Nuclear Magnetic Resonance

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Section: Introductioncontrasting

confidence: 49%

Section: Introductionmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 98%

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Determination of Molecular Orientational Order in Cold-Stretched Poly(p-phenylene vinylene) Thin Films by DECODER 13C NMR

Kropewnicki

Schaefer

Hehn

et al. 2002

Solid State Nuclear Magnetic Resonance

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“…For a particular orientation of the excitation beam it can be seen that the luminescence is only relatively weakly polarized despite the fact that the samples are known to be highly oriented. 4,14 The luminescence peak near 2.44 eV is due to the transition from the ground vibrational level of the first excited electronic state down to the ground vibrational level of the electronic ground state, and is denoted the ͑0-0͒ transition for the remainder of the paper. Vibronic transitions to higher vibrational levels of the electronic ground state occur at approximately 2.28 eV for the ͑0-1͒ transition, and 2.1 eV for the ͑0-2͒ transition.…”

Section: Resultsmentioning

confidence: 99%

“…It has been shown from infrared-absorption measurements that this produces highly oriented films. 4,14 The films were optically thick for excitation both parallel and perpendicular to the stretch direction. The oriented films were excited with frequency-doubled light from a modelocked Ti:sapphire laser.…”

Section: Introductionmentioning

confidence: 99%

Polarization dependence of the ultrafast photoluminescence of oriented poly(p-phenylenevinylene)

1997

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The ultrafast dynamics of excitons in stretch-oriented poly͑p-phenylenevinylene͒ ͑PPV͒ are studied by femtosecond time-resolved photoluminescence spectroscopy. It is shown that the total luminescence intensity at 1 ps after excitation is the same for excitation either parallel or perpendicular to the stretch direction. Thus the number of intrachain excitons initially generated is independent of the polarization of the excitation light. This indicates that direct interchain photogeneration processes are not important in PPV. A small polarization ratio is measured at very early times after excitation, and is consistent with the localized excitons having appreciable off-axis transition dipole moments. The confinement of the excitons places constraints on the maximum possible anisotropy of the luminescence. Significant differences between the luminescence rise and decay times are observed for different excitation and detection polarizations. These results are explained by a combination of nonradiative decay at quenching sites, whose strength depends upon the polarization of the excitation pulses, and exciton migration processes. ͓S0163-1829͑97͒09831-7͔ II. SAMPLE PREPARATION AND EXPERIMENTAL TECHNIQUEHighly oriented films of solution-cast PPV were prepared by stretching a film of a soluble precursor polymer with a

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Effect of comonomers on melt processability of polyacrylonitrile

Rangarajan¹,

Yang²,

Bhanu³

et al. 2002

J of Applied Polymer Sci

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This work is concerned with the feasibility of achieving melt-processable polyacrylonitrile copolymer systems as precursors for the manufacture of carbon fibers. Identification of suitable comonomers and achieving the optimum content of the comonomer were some of the main objectives of this investigation. It was seen that methyl acrylate (MA) was found to be suitable for enabling the melt processing of polyacrylonitrile (PAN), in terms of melt viscosity, time stability, and char yield. Below 10 mol % of MA, the PAN copolymer exhibited no flowability, even at very low molecular weights (ϳ 20,000). The long-range order inherently present in PAN is speculated to be broken down at a critical value of about 10% MA at 220°C in the PAN-based system, enabling its melt flowability. It was also seen that the incorporation of MA was seen to improve the temperature and molecular weight window of processability of the PAN system. The molecular weight cutoff for the 90/10 mol % acrylonitrile/methyl acrylate (AN/MA) system was about 50,000 at 220°C, whereas it was increased to about 100,000 in the presence of 15 mol % MA comonomer. Feasibility studies on the use of other comonomers such as higher acrylates and acrylamides were also conducted.

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Molecular orientation and conductivity in highly oriented poly(p-phenylene vinylene)

Cited by 15 publications

References 10 publications

Determination of Molecular Orientational Order in Cold-Stretched Poly(p-phenylene vinylene) Thin Films by DECODER 13C NMR

Determination of Molecular Orientational Order in Cold-Stretched Poly(p-phenylene vinylene) Thin Films by DECODER 13C NMR

Polarization dependence of the ultrafast photoluminescence of oriented poly(p-phenylenevinylene)

Effect of comonomers on melt processability of polyacrylonitrile

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