I have been doing some solubility tests recently and noticed that a lot of the samples exhibited characteristics of polymorphism. The sample that I held at 46C wasn't in melt, and on two occasions I was able to clearly see elevated MP temperatures - the first was a sample which began to melt at 54.1C, at 55.(~2)C there was melting in bulk and by 58.8C the sample was completely melted. The second sample began to melt at ~54.5C and was fully melted at 57.8C
The study produced several different morphologies in the end, with no clear correlation yet between those samples with the elevated MP and the shape of the dry solid. In fact, those samples each gave something different - crystals, needles, and a structure which resembles a spherulite.
There is no clear cut trend actually between any of the final forms with the testing conditions the respective sample was subjected to, and it's making my analysis difficult - the spherule shapes at first seemed to be formed from either rapid heating rates or else a rapid quench from high temperatures, but then they started appearing in samples that never got heated past 40C. I can't tell definitely if this is a polymorph but it seems so, since generally the structures are clear - to - white with a surrounding yellow amorphous portion around the bottom rim of the vial. A couple examples also seem to grow around an 'impure' inclusion which is nothing other than a small yellow crystal.
Regarding the needles, I haven't seen these before either. They are clearly different from the dendritic patterns produced from vapor along the walls of a glass, and seem to exist within some sort of temperature regime, from 36.5C - 68C in my study, with the longest needles formed at 46.0C.
I don't know how to tell for sure if these two are polymorphs or just exhibiting altered habits, but it kinda seems like polymorphism to me. The study from the article says the yellow amorphous mass is a polymorphic form, but what about these other structures.. I don't know.
I also would like to see a study which investigates polymorphism in salts, and what forms survive the conversion to freebase.
Pictures of some of these different forms below.
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