I have done DSC on some carboxylic acids and the results for all of them show two peaks in each melting curve. I was wondering if this because of the dimer-monomer forms?
Please refer the followig literature
Saturated carboxylic acids and their low molecular weight derivatives
US 5157068 A
It is not possible to answer with the data you have provided. Each fatty acid is different. it is possible that they are different types of crystal formation , but you can not say without knowing the other .
read this: http://link.springer.com/article/10.1007/s11746-009-1423-2
Observe the TG curve in the same temperature. If it occurs weight loss, decomposition following melting is posible.
I think this may be due to polymorphism (different solid phases; this may be the suggestion by Marco Signorelli); see "Latent heat characteristics of fatty acid derivatives pursuant phase change material applications" in Chemical Engineering Science, Volume 58, Issue 9, May 2003, Pages 1751–1763. There are example of thermograms with polymorphs.
I think that Marco, Peter and myself made a good synthesis of the polymorphism that seems to be frequent for these compounds.
Dear Pineda thanks! There is no signficant weight loss so is it really enough to say that we do not have decomposition in this case? i.e is wiight loss a necessary sign of decomposition?
Dear Jean- Francois and Peter
Thank you very much for your great comments. According to the papers you have suggested I also think polymorphism is the real reson of double melting peak. Thanks
The point raised by Pineda mais be tested by TG (thermogravimetry). In general a gas emission (vaporization, solvent evaporation, decomposition...) occurs on a wide temperature range.
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