We have observed a loss peak shift from 158 Hz to 100 Hz in dynamical mechanical analysis (DMA) of a 5mm x 20mm x 20mil (0.5mm) film of a PDMS-based (polydimethylsiloxane) fouling-release paint (Intersleek) as we traverse the glass transition (Tg) from -130 C to 100C. The decrease in frequency appears consistent with an increase in free volume that accompanies traversing the Tg. Has anyone seen a published report of a loss modulus vs frequency characterization of a Tg in any materials or in a material crossing some other critical temperature?
It is well known that tan delta as obtained from DMA has a frequency dependence in polymers, around the glass transition temperature. This can be eventually observed also in the temperature dependence of the modulus. I can try to look at your data, in particular if you can provide the dependence of tan delta on temperature, Typically, I will need at least 5 frequencies. I would try to start the measurements from -150 C for PDMS, in order to be certain that the whole dependence is captured. Please feel free to contact me at chiparaATyahoo.com.
Mircea
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