|Keywords:||Supercooled liquids; Isochronal superposition; Isomorph theory; Dielectric spectroscopy; High pressure|
|Full text PDF:||http://rudar.ruc.dk/handle/1800/18465|
This thesis investigates whether it can be shown experimentally if different types of liquids obey isochronal superposition. This investigation holds importance because a new theory, the isomorph theory, predicts that van der Waal liquids obey isochronal superposition. A definition of isochronal superposition, as well as those of Time-Pressure-Superposition and Time-Temperature-Pressure-Superposition, is established. Isochronal superposition is investigated for the dielectric relaxation spectrum. Dielectric measurements are made on four different liquids on a high pressure setup in relation to this project. Furthermore, data on two other liquids are included in this investigation. Two liquids studied are hydrogen bonded liquids, while four of them are van der Waal liquids. The high pressure measurement equipment used is relatively new and it is therefore first scrutinised before use in this thesis. Different measures, with the purpose of deciding to which degree a liquid obeys respectively isochronal superposition and Time-Temperature-Pressure-Superposition, are developed. These measures are based on the half width at half depth and the area deviation between the dielectric relaxation spectra. From these measures, it is concluded that the investigated van der Waal liquids obey isochronal superposition better than the investigated hydrogen bonded liquids. It is furthermore estimated that the investigated van der Waal liquids obey isochronal superposition and that some also obey Time-Temperature-Pressure-Superposition. It is concluded, that the studied hydrogen bonded liquids obey neither Time-Temperature- Pressure-Superposition nor isochronal superposition. The results follow the prediction of the isomorph theory and raises the question whether more liquids obey isochronal superposition. Further investigation could conclude whether van der Waal liquids in general obey isochronal superposition.