Correlations between PALS and diffusivities in amorphous polymer–solvent systems

Correlations between positron annihilation lifetime spectroscopy (PALS) measurement and diffusivities in polymer solutions were established, with the help of the Simha–Somcynsky (SS) equation-of-state (EOS) and the free-volume theory. Mean hole volume probed by PALS was employed to predict the free volume available for solvent transport and solvent diffusion coefficient. The predictions of infinite dilution diffusion coefficients of four organic solvents in two common polymers were generally consistent with the published experimental values. Hole size distribution from PALS results was also investigated to prove the reliability of this new approach.

f F By introducing the SS hole theory into the free-volume theory, a modified diffusion model has been developed to correlate the properties of free-volume holes from PALS measurement with solvent diffusion coefficients in amorphous polymers. The mean size of hole volume detected by PALS can be used to calculate the free volume available for solvent transport and hence the solvent diffusivities. The calculated diffusion coefficients of four organic solvents (i.e., toluene, ethylbenzene, o-xylene and hexane) in PMMA and PVAc were generally in a good agreement with experimental data. Furthermore, the analysis of hole size distribution reaffirmed the reliability of this approach. It is reasonable to expect this approach provide new insight into the effect of the detailed information of polymer holes on solvent diffusivities with further study.