|Refleksion, 1, bachelormodul. modul, 2007/2008, id:246|
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This project deals with the relationship between the mechanical and dielectric properties for supercooled viscoelastic liquids at temperatures above the glass transition temperature TG of liquids. Mechanic and dielectric measurements have been made for the liquids; 1,2 propanediol and methyl m-toluate. It is shown how the measurements differ frrom the basic models; Maxwell and Debye. The relaxation timesT of the liquids are found and it is shown, that the Vogel-Tammann-Fulcher equation is a good description of the relationship between temperature and relaxation time, for both mechanical and dielectric measurements. By using this equation, the glass temperature of the liquids is determined. Moreover the project shows, that the relaxation time of the mechanical measurements are shorter than the dielectric at a given temperature. We have examined whether the liquids obey time-temperature superposition (TTS), for the dielectric as well as the mechanical measurements. In view of this it is shown, that the top of the alpha-relaxation for the mechanical measurements are wider than for the dielectric. The maximum dielectric loss (formel) for 1,2- propanediol is found to be relatively high about 15-19, whereas for methyl m-toluate it is determined to be approximately low, about 1-2. The minimum slope is determined and its association with the maximum dielectric loss of the liquids have been found. Furthermore we estimatem the maximum loss of shear modulus (formel) as a function of minimum slope. It is shown, that there is tendency for liquids with high maximum dielectric loss, to have a numerical minimum slope around 0.5. It has been found, that the same relation between the maximum loss of shear modulus and minimum slope applies. Finally it is shown, that liquids, which obey TTS, has a numerical minimum slope around 0.5 (formel) 0.1.