Mutual and Thermal Diffusivities in Binary Mixtures of Polystyrene with Dissolved N2 or CO2 by Dynamic Light Scattering

Abstract In physical foaming processes of thermoplastics, a liquid mixture consisting of a molten polymer with a dissolved blowing agent is extruded through a die or injected into a mold. The morphology of the foam matrix strongly depends on the mutual diffusion coefficient D 11 of the liquid polymer-blowing agent mixture. For a better understanding of the underlying physical mechanisms during the foaming process and the development of corresponding models, accurate knowledge of D 11 is needed. This work reports on the simultaneous measurement of D 11 and the thermal diffusivity a of liquid mixtures consisting of polystyrene melts with dissolved nitrogen (N 2 ) or carbon dioxide (CO 2 ) at mass fractions w solute up to 0.003 or 0.02 and temperatures T between (433 and 533) K using dynamic light scattering (DLS). The determined D 11 range is between (1 and 4) × 10 9 m 2 ⋅s −1 and are slightly larger for the mixtures containing N 2 at a given T and w solute . D 11 could be determined with an average expanded relative uncertainty of 18%. Considering all investigated state points and the achieved experimental uncertainties, both D 11 and a are independent on the amount of dissolved gas, despite relatively large mole fractions of the dissolved blowing agents x solute of 0.997 and 0.93.