SYMPOSIA PAPER Published: 01 January 2001

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


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 /( ATs νω) [1 + (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.

Author Information

Wunderlich, B
The University of Tennessee, Knoxville, TN Chemistry and Analytical Sciences Division at Oak Ridge National Laboratory, Oak Ridge, TN, USA
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Developed by Committee: E37
Pages: 3–16
DOI: 10.1520/STP10696S
ISBN-EB: 978-0-8031-5452-0
ISBN-13: 978-0-8031-2887-3