Die Volumenretardation des Polystyrols nach Druck- und Temperatursprüngen

Abstract

Measurements of the isothermal-isobaric volume retardation in crosslinked and non-crosslinked polystyrene are reported. The measurements have been carried out applying the temperature-jump method, and, for the first time, also the pressure-jump method. For the measurements using the temperature-jump method a quartz-glassdilatometer has been used which allows the registration of volume changes of ±7·106 cm3. A pressure dilatometer has been developed for the measurements according to the pressure-jump method which permits volumemeasurments of the same precision in the pressure-range between 1 and 60 atmospheres. The experimental results show that for the volume retardation of polystyrene a measurable linear region exists. For this case of linear retardation behaviour various kinetic theories predict an exponential time dependence of the deviation of the volume from the equilibrium value, which is due to the existence of a single retardation time. This result is not confirmed by our experiments. The volume retardation in the linear region — at least for polystyrene — can in no case be described in terms of a single retardation time, but only by a distribution of retardation times. It turns out, that the retardation function (distribution function of retardation times) in the linear region differs after a previous temperature change from that after a previous pressure change. This result can be confirmed by theoretical considerations which follow fromMeixner's thermodynamic theory of linear relaxation phenomena.