Mutual and Thermal Diffusivities in Polystyrene Melts with Dissolved Nitrogen by Dynamic Light Scattering

Abstract

Knowledge on diffusion coefficients in mixtures consisting of a polymer melt and a blowing agent is necessary for understanding and characterizing the bubble growth processes during foaming of thermoplastic polymers. Due to the lack of reliable literature data in process-relevant conditions, the diffusion coefficients are often assumed to be constant to solve the equations for bubble growth in polymer melts. This study demonstrates, for the first time, the applicability of dynamic light scattering for the characterization of molecular mass and thermal transport in binary mixtures consisting of a macromolecular polymer and a dissolved gas by the determination of mutual and thermal diffusivities in macroscopic thermodynamic equilibrium. In the present study, a mixture of polystyrene and nitrogen was selected as the model system, which has technical relevance. After evidencing that the obtained experimental signals are associated with hydrodynamic modes, the influence of pressure and temperature on mutual and thermal diffusivities is discussed and the results are compared with the literature. For the mixtures studied in this work, expanded experimental uncertainties (k = 2) of the obtained diffusivities have a minimum value close to 3% and are on average 13% for the thermal diffusivity and 7.4% for the mutual diffusivity.

Diffusivities in Binary Mixtures of n-Decane, n-Hexadecane, n-Octacosane, 2-Methylpentane, 2,2-Dimethylbutane, Cyclohexane, Benzene, Ethanol, 1-Decanol, Ethyl Butanoate, or n-Hexanoic Acid with Dissolved He or Kr Close to Infinite Dilution

“…The fundamentals and the application of the DLS method within thermophysical property research ,, and the use of the DLS method including the experimental realization for the accurate and simultaneous determination of a and D 11 in mixtures consisting of liquids with dissolved gases − ,− have been described in detail in the literature. Thus, only pertinent information about the DLS method and the experimental realization related to the analysis of Rayleigh scattered light is given.…”

Mutual Diffusivities of Binary Mixtures of Water and Poly(ethylene) Glycol from Heterodyne Dynamic Light Scattering

“…For molecular binary systems such as liquids containing a dissolved gas, DLS has proven to allow the accurate and simultaneous determination of mutual diffusivity D 11 and thermal diffusivity a in an absolute way [18][19][20][21]. The same also holds true for the determination of the translational particle diffusion coe cient D T in free media and under con nement in particulate systems consisting of isotropic particles dispersed in liquids [22] as well as of D T and the rotational particle diffusion coe cient D R in dispersions containing anisotropic particles [23].…”