I have a silicone material with the rheology data as shown in the attached image, that was performed using temperature sweep program from 45°C to 160°C.
I would like to understand why does the graph exhibits a double tan delta peak of the same material. What does a double tan delta peak mean from general materials point of view? Anybody has any hypothesis?
*repeated measurements also yield the same result.
Bear in mind that you tested your sample at different times which may account for variations in the values of tan delta.. If you are expecting same results at different times, I will advise you calibrate your rheometer instrument very well before testing and make sure same parameters are used and also don't perturb (I mean there should be no vibration or disturbance where you place the rheometer machine). Having said that, tan delta tells how solid-like or liquid-like a sample is. When a sample has tan delta below 1, it is solid-like and above 1 is liquid-like.
Does the sample maintain its integrity to such an extent that you can run a second heating ramp on the same sample?
The fact that G' increases at higher time (or temp) makes me suspect that there are structural changes taking place such as x-linking.
The height and shape of the tan delta peak change systematically with amorphous content
Hi Alan, doing heating ramps on a modern rheometer can be challengeing . Your heating rate (4-5°C/min) could be on the high side? I would suggest that you do a DSC + TGA as well to see if there are chemical changes happening. Did you monitor the Normal Force? (expansion/contraction)
Hi;
I think you have a change in the structure.
With my best regards
DearAlan,
In the rgeology peak, tan(δ) quantifies the balance between energy loss and storage. In your case, the growth of the overshoot peak is caused by reentanglement of the solution. The inset shows representative transient shear stress data at minimum G. The double peak maxima superpose indicates independent of filler particle size. It also indicates there is a high perturbation rate to the low shear stress of almost 3 Pa and subsequently high damping is seen.
Ashish
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