Comparative Thermal and Thermodynamic Study of Homologous series by Chromatography using Liquid Crystalline Stationary Phase

Abstract

This work consisted in the preparation and the study of a new stationary phase based on liquid crystals for gas chromatography applications. Most of the synthesized compounds that have the character of liquid crystals in their constitution include aromatic molecules. In addition, there is little work that replaces this type of molecules with heterogeneous molecules that have a liquid crystalline character. This study constitutes an approach for the synthesis of a new molecule azoesters involves a 1,3,4-oxadiazole unit instead of aromatic rings, and which exhibits liquid crystalline characters. A liquid crystal has been prepared and characterized. The thermodynamic characteristics of the n-alkanes for the filled column were studied by reverse gas chromatography. The intermediate products, as well as the mesogens obtained, were characterized by various experimental analysis techniques such as infrared spectrometry (IR) and nuclear magnetic resonance (NMR). The thermal properties of synthesized liquid crystal require the use of DSC technique. Thermodynamic parameters such as enthalpies, partial solution molar entropy and infinite dilution, were determined for the liquid crystal-solvent system. The thermodynamic quantities show that these values depend on the number of carbon atoms of the CL phase terminal substituent. The transition temperatures obtained by gas chromatography are in good agreement with those found by DSC.