I have DSC thermograms that have already being plotted. At specific points on the graph, values denoted as Integral in mJ, onset, peak and endset in oC are provided. While I understand that the values in J/g represent enthalpy what does the integral value in mJ denote. Is it possible to have more than one glass transition temperature on the same thermogram?
Hi Oluwaseyi,
The fact you're getting millijoule (mJ) instead of millijoule per gram (mJ/g) would suggest the sample weight was read or inputted when getting the thermograph. In my own experience DSC software often lets you input sample weight and recalculates.
As for Tg; it depends if you're looking at small molecules or polymers. Small molecules have comparably neat stepping offset in the ranging of 2-3 ° C with offset of < 0.5 W/g whereas polymers will have a larger offset and a Tg spanning 10's of ° C.
Hope this helps,
Pól
Glass transition being a typical second order phase transformation (for which no latent heat evoution or absorption is involved), it does not produce a peak in a regular DSC scan. Tg typically manifests itself as a change of slope in a DSC thermogram. One simple way is to draw a tangent on the initial straightline representing baseline. Draw another tangent on the slope. The crossover point is Tg.
Usually, all commercial DSC instruments are having an in-built data processing software, which can directly assist you to calculate Tg.
Some times, people use an advanced modulated DSC technique or even dilatometry can be used to characterize Tg.
As for your milijoule (mJ) unit is concerned, as rightly pointed out by Dr Pol, it incorporates the sample mass that you put on the DSC pan.
Hi
Based on the DSC graph we can find the Tg. Moreover the mJ indicates millijoule. It is the measure of amount of energy consumed or supplied to get the phase change.
Best
In my experience with a TA Instruments SDT650, you CAN see a glass transition in some cases on the DSC thermogram. I've measured glass transitions using a heating rate of 10K/min and a sample size in the 10-13 mg range. The transition presents itself as a very slight inflection that can typically result in a slightly lower baseline, but this is not always the case. Typically to find the glass transition, I'll examine the derivative of the DSC thermogram and you can see the rate changes much more obviously.
Thank you so very much learned friends. Your answers and input have been helpful. While I'm still open to more inputs, I think I am better informed than before
Regards
Hi
You can find the amount of energy required for undergo the phase transformation from glassy to rubbery
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