I am curious what it means when the loss modulus, E", never peaks during a DMA test (increasing temp / constant frequency). I would imagine that this material never dissipates energy over the course of the test, which seems odd. I would imagine there is some point where the energy put in would cause the chains to move. There is a clear tan delta peak as well, so there is definitely a Tg. What am I missing?
Also, just to make sure I am understanding a DMA run correctly. Another run did show the loss modulus spike about 30 C lower than the Tg (Here is a pic of the run: https://imgur.com/a/KMK47kT). This is an acrylate cured urethane elastomer. Does this means the energy being put in is enough to cause the chains to disassociate, but not enough to cause them to completely move around? I usually see the loss modulus spike near the Tg, but this sample is quite a bit lower. What would be the cause for the large gap between the loss modulus peak and the tan delta peak? Are the backbone chains moving, but the hydrogen bonded links still solid and finally break at the Tg?
Any insight you can share would be greatly appreciated.
Thanks!
Kim, Yong-Rak, D. N. Little, and R. L. Lytton. "Fatigue and healing characterization of asphalt mixtures." Journal of Materials in Civil Engineering 15, no. 1 (2003): 75-83.
Sometimes the E'' peak can appear weak, especially if you are looking in the log scale. If you have a clear tan delta peak there must be a E'' peak somewhere near the E' drop. Try to change the scale into linear.
About your second question, from your pic I could give two explanations for your results: you have a phase separation so that you have 2 Tgs, and therefore 2 tan delta and E" peaks, or you have strong alpha transitions, meaning some pretty strong Rouse or sub-rouse mobility, due to side chains or small backbone units that can move. Check some literature about acrylates, since I know, at least from an NMR point of view, that they show some pretty peculiar mobilities.
I guess you take Tg from DSC or DTA (both techniques differ) curves obtained with some heating rate (or you extrapolate to 0 heating rate). Maximum in E" is obtained for some frequecy. There is no dirrect correlation between both observed phenomenon.
Did you take into account the three phase model? You could read the paper by Hossemann (from 60s years) or the chaper 5 from Sestak J., Mares J.J., Hubik P. Glassy, Amorphous and Nano-Crystalline Materials.. Thermal Physics, Analysis, Structure and Properties (Springer, 2010)(ISBN 9048128811).
It is difficult to discussed about results if I do not see the original curves. If it not a problem, pease send me cures DMA and DSC/DTA. I will try to halp you. However, Denise is right in general, however comparison between NMR and DMA or DETA, it is other story. I guess she was thinking about solid state NMR.
@Adam Danch Yeah sorry, I was referring to solid state nmr, especially in time domain.
You may measure a well known substance with a well expressed loss peak to ensure that you have no errors in the measurement procedure.
Looking at the picture:
tan delta peak at - °C is matched by a E" large peak at about -20 °C (about 155 MPa)
tan delta peak at +88 °C is matched by a small E" peak at about +85 °C (about 50 MPa)
You have an E" peak with each tan delta peak. You need to remember that tan delta = E"/E' and therefore this is a small number when E' is high and is a small number when E' is low,.
I think the measured data look good and valid. You have two transitions - a sub zero Tg and another transition (also a Tg?) at 88 °C.
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