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Ultrafast nonexponential dynamics in a polymer glass forming liquid

J. Chem. Phys. 100, 1673 (1994); doi:10.1063/1.466595

Issue Date: 15 January 1994

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Abhijit Sengupta and M. D. Fayer
Department of Chemistry, Stanford University, Stanford, California 94305
The orientational dynamics of phenyl side groups in poly(methylphenylsiloxane) (PMPS) melts are examined over a broad range of viscosity/temperature (eta/T) using subpicosecond transient grating optical Kerr effect (TGOKE) measurements. Measurements on poly(dimethylsiloxane) are also reported. Following ultrafast (hundreds) of fs librational dynamics, the phenyl side group orientational dynamics occur over a range of times from 2 ps to a few hundred ps. The experiments were performed from 25 to 143 °C, resulting in eta/T changing by a factor of 40. In spite of the large change in eta/T, the side group dynamics remain unchanged throughout the entire temperature range. Comparison of the dynamics of PMPS in the melt and PMPS in dilute CCl4 solution shows that chain–chain interactions influence the phenyl side group dynamics in the melt. The dynamics are described as local orientational relaxation of phenyl groups in the microenvironments defined by the backbone geometry and side group steric interactions rather than rotational diffusion. The dynamics exhibit power-law behavior, t−alpha, over two decades of signal decay. Two possible physical processes that can give rise to a power-law decay are discussed. The relationship of the observed dynamics to the beta and alpha relaxations of glass forming liquids is also discussed. The Journal of Chemical Physics is copyrighted by The American Institute of Physics.
History: Received 29 July 1993; accepted 28 September 1993
Permalink: http://link.aip.org/link/?JCPSA6/100/1673/1
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KEYWORDS and PACS

Keywords
PACS
  • 64.70.Pf
    Equations of state, phase equilibria, and phase transitions Phase equilibria, phase transitions, and critical points of specific substances Glass transitions
  • 61.25.Hq
    Structure of solids and liquids; crystallography Studies of specific liquid structures Macromolecular and polymer solutions; polymer melts
  • 35.20.Jv
    Experimentally derived information on atoms and molecules; instrumentation and techniques Molecules Barrier heights (internal rotation, inversion); rotational isomerism, conformational dynamics
  • 78.47.+p
    Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation Time-resolved optical spectroscopies and other ultrafast optical measurements in condensed matter
  • YEAR: 1994

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PUBLICATION DATA

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