Effect of molecular size on cooperative dynamics of low mass compounds in polystyrene

O. Urakawa, E. Ohta, H. Hori, K. Adachi

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29 Citations (Scopus)


We studied the dielectric relaxation behavior of low mass compounds (LMC) mixed in polystyrene (PS). Specifically, LMCs that are used are alkyl-cyanobenzene (nCBz, n = 0), alkyl-cyanobiphenyl (nCB, n = 0, 1, 3, 5, and 7), and alkyl-cyanoterphenyl (nCT, n = 5), where n represents the number of carbon atoms of the normal alkyl groups of the LMCs. Owing to a much larger dipole moment of the cyano group than that of PS, only motions of the LMCs were observed. In a blend of 5CT (5 wt %)/PS, single relaxation process designated as a was observed. On the other hand, in nCB (5 wt %)/PS, partially overlapped two relaxation processes (α and β) were observed in the order of decreasing temperature. We assigned the a process to cooperative motions between the LMC molecules and the PS segments, and the β process to spatially restricted motions of the LMC molecules in the glassy state. In 0CBz (8 wt %)/PS, the α and β processes were observed in distinct temperature regions and the intensity of the a peak was comparable to that of pure PS, indicating that the 0CBz molecules do not move cooperatively with the PS segments. We conclude the existence of two critical sizes (I and II) of LMC in relation to cooperativity: when an LMC molecule is smaller than the size-I, the motions of the LMCs and PS segments decouple each other, but above the size-I, they become cooperative. Above the size-II, the spatially restricted motion (β-process) of LMC does not occur.

Original languageEnglish
Pages (from-to)967-974
Number of pages8
JournalJournal of Polymer Science, Part B: Polymer Physics
Issue number6
Publication statusPublished - Mar 15 2006

All Science Journal Classification (ASJC) codes

  • Condensed Matter Physics
  • Physical and Theoretical Chemistry
  • Polymers and Plastics
  • Materials Chemistry


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