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Segmental dynamics of disordered styrene–isoprene tetrablock copolymers

J. Chem. Phys. 116, 4707 (2002); doi:10.1063/1.1452109

Issue Date: 15 March 2002

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M. Doxastakis and K. Chrissopoulou
FO.R.T.H.-Institute of Electronic Structure and Laser, P.O. Box 1527, Heraklion, Crete, Greece

A. Aouadi
Max-Planck Institut für Polymerforschung, P.O. Box 3148, 55021 Mainz, Germany

B. Frick
Institute Laue Langevin BP 156X, 38042 Grenoble, France

T. P. Lodge
Department of Chemistry and Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455

G. Fytas
FO.R.T.H.-Institute of Electronic Structure and Laser, P.O. Box 1527, Heraklion, Crete, Greece
Max-Planck Institut für Polymerforschung, P.O. Box 3148, 55021 Mainz, Germany
The local segmental dynamics of four styrene-b-isoprene-b-styrene-b-isoprene (SISI) tetrablock copolymers with different styrene composition fs and constant total degree of polymerization N[approximate]120 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]0.8 nm suffices for the loss of local orientation correlations. The faster times of the BS experiment correspond to shorter displacements, [approximate]0.3 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. ©2002 American Institute of Physics.
History: Received 9 October 2001; accepted 28 December 2001
Permalink: http://link.aip.org/link/?JCPSA6/116/4707/1
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KEYWORDS and PACS

Keywords
PACS
  • 61.41.+e
    Structure of solids and liquids; crystallography Polymers, elastomers, and plastics
  • 78.35.+c
    Optical properties, condensed-matter spectroscopy and other interactions of radiation and particles with condensed matter Brillouin and Rayleigh scattering; other light scattering
  • 64.70.Pf
    Equations of state, phase equilibria, and phase transitions Specific phase transitions Glass transitions
  • 66.30.Hs
    Transport properties of condensed matter (nonelectronic) Diffusion in solids Self-diffusion and ionic conduction in nonmetals
  • 62.40.+i
    Mechanical and acoustical properties of condensed matter Anelasticity, internal friction, stress relaxation, and mechanical resonances
  • 81.40.Jj
    Materials science Treatment of materials and its effects on microstructure and properties Elasticity and anelasticity, stress-strain relations
  • 78.47.+p
    Optical properties, condensed-matter spectroscopy and other interactions of radiation and particles with condensed matter Time-resolved optical spectroscopies and other ultrafast optical measurements in condensed matter
  • YEAR: 2002

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ISSN:
0021-9606 (print)   1089-7690 (online)
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