Abstract
Rich polymorphism of ethosuximide compound (ETX) is described in detail using complementary thermal analysis methods. The paper shows as well the results of differential scanning calorimetry (DSC), of polarizing microscope observations (POM) and of X-ray diffraction (XRD) measurements taken using horizontal rotating capillary method. Molecular structure of ethosuximide favors appearance of a conformationally disordered (CONDIS) crystal phase CrI in its polymorphism. Ethosuximide is a good glass former, and glass of the CrI phase was observed even for 5 °C min−1 rate of cooling. Moreover, monotropic plastic crystal CrII phase was observed during heating above the CrI temperature range.
Highlights
Matter can exist in solid, melt and gas states
The value of difference between DSheat and DScool is equal around 3 J K-1 mol-1. It is similar as the value of difference that was found between smectic and nematic phases for a liquid crystal compound [18]. This observation suggests that differences between CrII and CrI crystal phases correspond to different orientational orders of ethosuximide compound (ETX) molecules in crystalline lattices
The peak separation corresponding to two phase transitions, which overlap to each other, may be observed, if the differential scanning calorimetry (DSC) experiment is performed with smaller temperature change
Summary
Matter can exist in solid, melt and gas states. The large amplitude motions as translations and rotations of molecules, internal rotational and/or conformational changes determine the differences between fluid (IL) and solid states. Monotropic plastic crystal CrII phase was observed during heating above the CrI temperature range. Thermooptical analysis (TOA) was performed by TOApy program [15] based on digitalized images of ETX microscopic textures observed on cooling and heating experiments.
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