Да, если процессы обратимые. Может сказаться кинетический фактор, который выдаст систематическую ошибку.

I have some experience in using precise ultrasonic velocity measurements to ensure the completion of polymerisation in the monomer zel while using Gama radiation. And then using polymer Perspex samples for irradiation measurements.

I feel that use of accurate ultrasonic velocity measurements over the sample/materials would be of much more effective for monitoring the percentage polymer crystallinity...

Нужно определить коэффициент. Его можно определить, если использовать еще один метод измерения кристалличности, например определение плотности методом дилатометрии.

Palanichamy Perumal Thank you for your suggestion.

I am currently doing my master thesis, which means I am limited with the tools I have. DSC, GPC, ATR-FTIR and Karl-Fisher water content are the only methods I can use at the moment.

В качестве дилатометра подойдет любой пикнометр, стеклянный сосуд для измерения плотности и весы. Очень просто.

At Tg, crystallization occurs, as demonstrated by X-ray diffraction, for example. It is usual to read that crystallization is exothermic. However, since it is a thermally activated process, crystallization is endothermic. You're right to think that at this temperature, other phenomena occur that cannot be explained by differential thermal analysis alone. By combining complex impedance measurements, measurements representative of interactions between electromagnetic waves and matter, mechanical measurements and conduction measurements, we can ensure that processes at Tg are linked to electronic excitations. Successive temperature cycles and, when the material permits, luminescence, permittivity, Young's modulus and density measurements show that at Tg, dielectric losses are accompanied by the destruction of "extended defects" (dislocations or clusters of atoms around electron traps) and the formation of nanocavities. Exohermal flow at Tg is due to entropy jumps observed under shock techniques, for example. You are therefore right not to compare the enthalpy of fusion and the enthalpy of the process at Tg, as these are totally different processes. To complete and interpret your results, if possible, characterize the electrical charge properties of your materials, but be careful before undertaking these measurements, find out about the charging and discharging mechanisms and the suitability of the techniques for characterizing them. In principle, before the summer, I think you'll be able to find information in the journal of applied physics/perspective that will help you in your research. All the best.

Claude Le Gressus

Claude Le Gressus Hello, thank you for your detailed answer.

I am not sure why you are reffering to the Tg in your answer, since with "melting peak" I meant the peak around the Tm not the glass transition. I guess similar concepts also apply for that then.

Dominik

Excuse my mistake. What I answered you concerns what happens at Tg but your question did not concern this temperature.

Dear Dominik, I have few experience in using precise ultrasonic transit time/velocity measurements for effectively characterising the microstructures, precipitates, residual stresses, etc.. I am herewith uploading two of my research for you and to the users of Researchgate.

Hope these would be some use to you....

Palanichamy Perumal That sounds very interisting, i would love to try that. Unfortunately i do not have access to a machine for ultrasonic transit time/velocity measurements. I only have a DSC available to perform my measurements.

Thank you anyway.

Dear Dominik, You are in Germany I suppose... M/s. Krautkramer GmbH company is a Germany based company only. We have used the Flaw Detectors of that company left and right for the purpose of non-destructive evaluation of flaws in austenitic steel weld joints. If you approach them then they would certainly help you.

Then if you have an ultrasonic thickness meter which can use 10 MHz transducer then you can also use that for measuring ultrasonic velocities of solid and liquid samples. When the material, including polymers, undergoes rapid change like polymerization, recrystallisation, precipitation, etc... then ultrasonic wave interaction with that materials property is expected give that information basically through wave attenuation and velocity changes. By accurately measuring these two parameters one can even quantitatively assess/calculate or predict that physical parameter of interest.....

All the best!.....

Dear Dominik Hüfner

Using the crystallization peak instead of the melting peak to calculate the percentage crystallinity of a polymer sample is not common practice, but it can be done under certain circumstances. However, it's essential to consider the limitations and potential differences in the results.

Here are some points to consider:

Clarity of Peaks: If the crystallization peak is well-defined and distinct from other peaks or background noise, it may provide a more reliable measure of the crystalline content compared to a broad or ambiguous melting peak.

Peak Shape and Background Effects: As you mentioned, the melting peak might be broadened or influenced by factors such as thermal history, impurities, or molecular weight distribution. Using the crystallization peak, which is less affected by such factors, could potentially yield more consistent results.

Enthalpy Differences: The enthalpy of crystallization and melting are typically different for the same polymer sample. This means that even if you can calculate the percentage crystallinity using the crystallization peak, the value may not be directly comparable to the traditional method based on melting enthalpy.

Relationship Between Crystallization and Melting Peaks: While there's no simple conversion factor between crystallization and melting enthalpies, there is a relationship between the two processes. The crystallization enthalpy represents the energy released when the polymer transitions from the melt to the crystalline state, whereas the melting enthalpy represents the energy absorbed when the polymer transitions from the crystalline to the melt state. These enthalpies are related thermodynamically but can differ due to factors such as kinetics, thermal history, and sample preparation.

If you choose to use the crystallization peak for calculating crystallinity, it's essential to validate this approach by comparing the results with other methods or characterizations whenever possible. Additionally, ensure that the conditions of crystallization and melting measurements are consistent to minimize variability.