It starts with TTS

One of the interesting, and in a way depressing, side effects of the separation of Dynamic Mechanical Analyzers (DMA) from other rheometers is the loss of understanding of many of its applications. Loss of understanding may be the wrong term, but it will serve.

Eighty to ninety percent of the people using DMA are looking for the glass transition (Tg). Some also want the modulus at room temperature to avoid having to run a Young’s modulus experiment in a Universal testing machine. Mostly these people are looking at the tan delta and the storage modulus (E’). Aerospace is the one exception I am aware of, as they often use a peak in the loss modulus (E”) to indicate Tg.

Before we even get to using frequency information and the master curve, there are other transitions that affect performance like the alpha star or the beta transition. The rubbery plateau’s moduli is related to crosslinking or entanglements, melting has power-law relationships, etc.

Frequency info lets us determine what a transition is, how changes in frequency will ship it, etc but it really becomes important when it is used to create the master curve, by shifting data along the frequency axis related to the temperature it was collected at. (Yeah, this is a gross simplification.) One the shift is complete, we have a curve that characterizes the material from very low frequencies, where we’d died of old age before measuring, to very high frequencies, where the instrument would shake itself apart.

From here, we can investigate relationships like the van Gurp-Palmen plot, the relaxation or retardation moduli, predict creep behavior and fit models. We could also invert the curve as time is the inverse of frequency. It’s kinda magical, and it often doesn’t give meaningful data. I’m still looking for the original reference so if anyone knows, please share.

But there is a lot of information there and since people often run temperature scans at multiple, it’s not costing any more time.