Dynamics of glass-forming liquids. VIII. Dielectric signature of probe rotation and bulk dynamics in branched alkanes

Shervin Shahriari, Andrea Mandanici, Li Min Wang, Ranko Richert

Research output: Contribution to journalArticle

35 Scopus citations

Abstract

We have measured the dielectric relaxation of several glass forming branched alkanes with very low dielectric loss in the frequency range 50 Hz-20 kHz. The molecular liquids of this study are 3-methylpentane, 3-methylheptane, 4-methylheptane, 2,3-dimethylpentane, and 2,4,6-trimethylheptane. All liquids display asymmetric loss peaks typical of supercooled liquids and slow β relaxations of similar amplitudes. As an unusual feature, deliberate doping with 2-ethyl-1-hexanol, 5-methyl-2-hexanol, 2-methyl-1-butanol, 1-propanol, or 2-methyltetrahydrofuran at the 1 wt% level generates additional relaxation peaks at frequencies below those of the α relaxation. The relaxation times of these sub-α-peaks increase systematically with the size of the dopant molecules. Because these features are spectrally separate from the bulk dynamics, the rotational behavior and effective dipole moments of the probes can be studied in detail. For the alcohol guest molecules, the large relative rotational time scales and small effective dipole moments are indicative of hydrogen bonded clusters instead of individual molecules.

Original languageEnglish (US)
Pages (from-to)8960-8967
Number of pages8
JournalJournal of Chemical Physics
Volume121
Issue number18
DOIs
StatePublished - Nov 8 2004

ASJC Scopus subject areas

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry

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