STP1402

    Temperature-Modulated Calorimetry of Polymers with Single and multiple Frequencies to Determine Heat Capacities as Well as Reversible and Irreversible Transition Parameters

    Published: Jan 2001


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    Abstract

    Temperature-modulated differential scanning calorimetry (TMDSC) generated with a centrosymmetric saw-tooth oscillation can be considered to be a sinusoidal modulation with multiple frequencies. Different harmonics of the Fourier series of the heat-flow rate and heating rate of a single sawtooth-modulation can be deconvoluted to extract data pertaining to different frequencies. In order to give the higher harmonics similar amplitudes, a complex, but simple-to-program, sawtooth-modulation is generated for the harmonics 1,3,5,7 and 9. In this fashion a single experiment can produce a frequency-dependent analysis under identical thermal history. Application of this method to TMDSC includes the calibration for heat capacity determination of high precision, even if steady state and a negligible temperature gradient are not achieved. The measurement of the frequency (ω) dependence of the heat-flow rate (AHF) and sample temperature (ATs) allows to evaluate the expression: CP=AHF/(ATsνω)[1+Caret(τνω)2]0.5 where the relaxation time τ is to be determined empirically from the multiple data generated by the single run. Typical values for the relaxation time for commercial calorimeters are between 3 and 9 s rad-1. Frequency-dependent, apparent reversing heat capacities in the glass transition region and within first-order transition regions may also be analyzed to study local equilibria in globally metastable polymeric solids.

    Keywords:

    temperature-modulated DSC, multifrequency modulation, metastable polymer, heat capacity, latent heat, phase transition, glass transition, first-order transition


    Author Information:

    Wunderlich, B
    The University of Tennessee, Knoxville, TN

    Chemistry and Analytical Sciences Division at Oak Ridge National Laboratory, Oak Ridge, TN


    Paper ID: STP10696S

    Committee/Subcommittee: E37.01

    DOI: 10.1520/STP10696S


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