I am comparing different emulsions freeze-thaw stability using TA Q-1000 with aluminum pan, around 15 mg of liquid samples (emulsions). I expected to see an exothermic crystallization peak backward towards less temperature, however, We saw a very big loop (that happened around -20 degrees), which should be related to the effect of exothermic crystallization.
However, my question is why there is no article about this effect? Why many researcher reported it as normal exothermic peak (one example is also attached)? How did they get normal peak although they used the same TA instrument and very similar emulsion.
What do you suggest in reporting the data for article?
Thank you again for your precious help and support.
Hy, I experienced a looping in concentration measurement during very fast crystallization in a mixed solvent system. This is called oiling out and I think that you should have experienced something like this. this can be a result of very fast cooling and desappear after sometime. try to adjust your experiment condition
Hysteresis can be due to the size effect and supersaturation. With a decrease in the particle radius, their melting point decreases. Supersaturation also depends on the size of the emulsion.
I will suggest trying out the experiment using lesser sample mass; ideally less than 5mg.
This looping phenomenon is the effect of high energy that is released during exothermic crystallization on cooling. The crystallization heat exceeds the capacity of the instrument's cell to maintain a programmed cooling rate. If you plot derivative of temperature (with respect to time) against temperature or time in the cooling run, you will probably see deviations in the graph in the crystallization region, rather than the expected flat horizontal line.
Reducing the sample mass to 3-5 mg will cause the loop to disappear.
You may find useful the following RG discussions: https://www.researchgate.net/post/Does_anyone_know_why_my_DSC_peak_is_overlapping https://www.researchgate.net/post/Why_is_the_onset_temperature_on_the_DSC_curve_lower_than_the_peak_temperature https://www.researchgate.net/post/2nd_spike_on_DSC_curve_can_anyone_tell_me_what_is_it
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