Mekaniske og dielektriske målinger på 1,2-propandiol og methyl m-toluate

Abstract

Denne rapport beskæftiger sig med sammenhængen mellem de mekaniske og dielektriske egenskaber i underafkølede viskoelastiske væsker over væskernes glastemperatur Tg. Der foretages dielektriske og mekaniske målinger på stofferne; 1,2-propandiol og methyl m-toluate. Det vises hvordan målingerne afviger fra de grundlæggende modeller; Maxwell og Debye. Stoffernes relaksationstid findes og det vises, at Vogel-Tammann-Fulcher ligningen er en god beskrivelse af sammenhængen mellem temperatur og relaksationstid både for de dielektriske og mekaniske målinger. Ud fra denne bestemmes stoffernes glastemperatur. Derudover vises det, at relaksationstiden for de mekaniske målinger er kortere end for de dielektriske ved en given temperatur. Det undersøges om de dielektriske og de mekaniske målinger på stofferne opfylder time-temperature superposition (TTS). På baggrund af dette vises det, at -relaksationens top, for de mekaniske målinger, er bredere end for de dielektriske. Det maksimale dielektriske tab "00 max for 1,2-propandiol findes til at være forholdsvis høj omkring 15-19, hvor den derimod bestemmes for methyl m-toluate til at være lav omkring 1-2. Minimum slope bestemmes og en sammenhæng mellem denne og væskernes maksimale dielektriske tab findes. Derudover sammenholdes shearmodulets maksimale tab G00 max for væskerne med væskernes minimum slope. Der vises en tendens til, at væsker, med et højt maksimalt dielelektrisk tab, har en minimum slope, som ligger numerisk over 0.5, hvilket ligeledes gør sig gældende for sammenhængen mellem shearmodulets maksimale tab og minimum slope. Endeligt vises det at væsker, som opfylder TTS, har en numerisk minimum slope på 0.5 ±0.1.

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 the 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 from the basic models; Maxwell and Debye. The relaxation times 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 -relaxation for the mechanical measurements are wider than for the dielectric. The maximum dielectric loss "00 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 estimate the maximum loss of shear modulus G00 max 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 ±0.1.