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          Institute: MPI für Polymerforschung     Collection: MPI Polymerforschung     Display Documents

ID: 28537.0, MPI für Polymerforschung / MPI Polymerforschung
Segmental dynamics of disordered styrene-isoprene tetrablock copolymers
Authors:Doxastakis, M.; Chrissopoulou, K.; Aouadi, A.; Frick, B.; Lodge, T. P.; Fytas, G.
Date of Publication (YYYY-MM-DD):2002-03-15
Title of Journal:Journal of Chemical Physics
Journal Abbrev.:J. Chem. Phys.
Issue / Number:11
Start Page:4707
End Page:4714
Review Status:No review
Audience:Not Specified
Abstract / Description:The local segmental dynamics of four styrene-b-isoprene-b- styrene-b-isoprene (SISI) tetrablock copolymers with different styrene composition f(s) and constant total degree of polymerization Napproximate to120 has been studied in the disordered state in the nano-picosecond time scale, by incoherent quasielastic neutron (QENS), and Brillouin (BS) and depolarized Rayleigh (DRS) light scattering. Far above the glass transition temperature, all three techniques demonstrate the presence of two distinct time scales from which the fast segmental relaxation was quantitatively resolved. This process is associated with the mobility of the polyisoprene (PI) component, and is moderately slower and possesses a broader distribution of relaxation times than in bulk PI. The comparison between the correlation times of DRS and the characteristic times of QENS suggest that segment (hydrogen nucleus) diffusion over a distance of approximate to0.8 nm suffices for the loss of local orientation correlations. The faster times of the BS experiment correspond to shorter displacements, approximate to0.3 nm. These results demonstrate that the segmental dynamics of the PI are much faster than would be inferred from the monomeric friction factor of PI previously extracted by diffusion and viscosity measurements in the same tetrablock matrices. This, in turn, indicates a substantial local spatial heterogeneity in the segmental dynamics. The slow process is due to the PS segments, which do not relax, appreciably on the time scales accessible here. (C) 2002 American Institute of Physics.
Comment of the Author/Creator:Date: 2002, MAR 15
External Publication Status:published
Document Type:Article
Affiliations:MPI für Polymerforschung
External Affiliations:FORTH, Inst Elect Struct & Laser, POB 1527, Iraklion, Crete, Greece; Inst Max Von Laue Paul Langevin, F-38042 Grenoble, France; Univ Minnesota, Dept Chem, Minneapolis, MN 55455 USA; Univ Minnesota, Dept Chem Engn & Mat Sci, Minneapolis, MN 55455 USA
Identifiers:ISI:000174210100033 [ID No:1]
ISSN:0021-9606 [ID No:2]
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