Étude thermodynamique de 4 cristaux liquides contenant des substituants dioxyethylene par analyse enthalpique differentielle et chromatographie en phase gazeuse

Abstract
A thermodynamic study of 4 liquid crystals with DOE substituents using gas chromatography are carried out. The 4 compounds have the same mesogenic part; they differ by the partial or total substitution of the terminal chain heptyloxy with 2-(2-methoxyethoxy)ethoxy (DOE). The thamal properties of the 4 compounds are determined by differntial scanning calorimetry. The knowledge of the gas chromatographic specific retention volume of a serial geometric isomers obtained by using the 4 liquid crystals as stationary phases allow to calculate their thermodynamic data: activity coeffients, enthalpies and entropies of solution. In the other hand, the support influence on the thermal properties are investigated. The results founds show that this parameter is not negligible but disappear when the coating increases. For silica, the transitions (melting, clarification) are apparent only when the coating is higher than 50%. With Chromosorh P, 5% of coating are sufficient to observe the transitions.