I have read some papers. The formula for calculating the crystallinity in DSC is based on the reference of 100% crystallinity. The fraction of crystallinity is a ratio of the melting enthalpy of sample over the melting enthalpy of 100% crystalline reference. Some questions:
1. Can I use 100% amorphous for a reference instead of 100% crystallinity? If so, which formula should I use?
2. Some other papers calculated the fraction of crystallinity by a (100%-ratio of crystallization enthalpy of sample over the crystallization enthalpy of 100% amorphous reference). I am not sure if the second formula can be used.
Hope I can get your answers.
Thank you
my understanding:
1. Not sure if you can use 100% amorphous, since the formula will just become 100% minus the amorphous portion of the material, which is essentially the same as crystallinity. Plus, how to define amorphous enthalpy from a DSC curve? Anything that's not crystalline will show as flat line deviating from the empty cell baseline
2. I simply use melting enthalpy/ full crystalline enthalpy formula
@ Jiangsha- Thank you for your answer.
My understanding for the formula using 100% amorphous as a reference material is that
- For the reference material, we can get the enthalpy of crystallization
- For a partial crystalline, the other enthalpy of crystallization can be also obtained by DSC. Then, a relative ratio of enthalpy of crystallization between partial and 100% amorphous reference will give the fraction of crystallization.
Since I have a 100% amorphous material. This formula will be useful for me. However, I just want to know if anyone know this formula. Please share to me if you have any doccument talk about it.
If you use a reference material which is 100% amorphous, you will not get any endothermic peak in the DSC analysis, so you will not be able to calculate any enthalpy. Amorphous materials do not melt, instead they pass through a glass transition when heated.
That calculation, as Jiangsha Meng said, will only work for (approximately) 100% crystalline material as the reference.
I guess you have assumed that all the samples will reach 100% crystallinity after "crystallization". This is generally not true.
Of course there are no 100% crystalline materials, but the reference should be as much crystalline as possible.
Good evening Nguyen,
Apologies for coming quite late into this discussion.
A great paper by Sandrine Guinot.....
International Journal of Pharmaceutics 192 (1999) 63–75
....has attempted to determine the percentage amorphous content by using a highly amorphous standard.
Please ignore the modulated part of her paper, if you can not clearly see the Tg, heat-cool cycle over the glass transition region.
In summary from the paper, the step change in the heat capacity or base line is directly proportional to the amount of amorphous material present.
However please note there will be a limit of detection issue, as it is impossible to get 100% amorphous or 100% crystalline standards, so for very small amounts of amorphous content you will need to think about the limits of your standard.
Regards Paul
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