Application of the Compensated Arrhenius Formalism to Dielectric Relaxation

Matt Petrowsky and Roger Frech*
Department of Chemistry and Biochemistry, University of Oklahoma, Norman, Oklahoma 73019
J. Phys. Chem. B, 2009, 113 (50), pp 16118–16123
DOI: 10.1021/jp907018s
Publication Date (Web): November 19, 2009
Copyright © 2009 American Chemical Society

Abstract

Abstract Image

The temperature dependence of the dielectric rate constant, defined as the reciprocal of the dielectric relaxation time, is examined for several groups of organic solvents. Early studies of linear alcohols using a simple Arrhenius equation found that the activation energy was dependent on the chain length of the alcohol. This paper re-examines the earlier data using a compensated Arrhenius formalism that assumes the presence of a temperature-dependent static dielectric constant in the exponential prefactor. Scaling temperature-dependent rate constants to isothermal rate constants so that the dielectric constant dependence is removed results in calculated energies of activation Ea in which there is a small increase with chain length. These energies of activation are very similar to those calculated from ionic conductivity data using compensated Arrhenius formalism. This treatment is then extended to dielectic relaxation data for n-alkyl bromides, n-nitriles, and n-acetates. The exponential prefactor is determined by dividing the temperature-dependent rate constants by the Boltzmann term exp(−Ea/RT). Plotting the prefactors versus the static dielectric constant places the data on a single master curve for each group of solvents.

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History

  • Published In Issue December 17, 2009
  • Article ASAPNovember 19, 2009
  • Received: July 23, 2009
    Revised: October 21, 2009

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