What does a Loss Modulus Curve Measure
What does a Loss Modulus Curve Measure
(OP)
Hi all,
I've just been handed a data summary from a DMA test. I'm trying to find help interpreting a "loss modulus" curve.
I know that the Tg can be taken from the peak in the Loss Modulus but I want to understand what is happening in the material to cause this peak?
Thanks in advance for your help!
Helen
I've just been handed a data summary from a DMA test. I'm trying to find help interpreting a "loss modulus" curve.
I know that the Tg can be taken from the peak in the Loss Modulus but I want to understand what is happening in the material to cause this peak?
Thanks in advance for your help!
Helen





RE: What does a Loss Modulus Curve Measure
A Google search for "loss modulus definition" gave me this link that describes it very well.
http://www.polyacs.org/nomcl/pmse.mechterm.html
"For dynamic experiments, the favorite today for many purposes, a sign wave is imposed on the sample. The wave may be of constant or variable frequency. Then, the modulus is split into two quantities, a storage modulus, E’, a measure of the energy stored during a cycle, and the loss modulus, E’’, a measure of the energy lost. The quantity E’’ has a maximum at the glass transition of the polymer, where it softens from a glassy to a rubbery polymer. The quantity tand is the ratio of E’’ to E’."
There is not any memory with less satisfaction than the memory of some temptation we resisted.
- James Branch Cabell
RE: What does a Loss Modulus Curve Measure
I'm trying to understand what is happening to the structure of the polymer as it goes through the Tg, any help would be very much appreciated!
RE: What does a Loss Modulus Curve Measure
The Tg is where the polymer chains undergo crankshaft motions with about 15 units participating (if I remember correctly).
Also the Tg is not a well defined, constant parameter, it depends very much on testing speed so if you were to rerun your DMTA at a higher frequency you would get a lower Tg and if the DMTA were run at a lower frequency then the Tg would be higher.
It is rather important to realise that polymer properties are time/frequency dependent (as described by the famous WLF equation). For example if you were to use your material for sound/vibration damping you would find the damping factor (tan delta) changes with temperature and frequency so the damping would be uneven for different frequencies.
There is not any memory with less satisfaction than the memory of some temptation we resisted.
- James Branch Cabell
RE: What does a Loss Modulus Curve Measure