Mutual diffusion in aqueous solution of poly(ethyleneglycol) samples. Some comments on the effect of chain length and polydispersity

Abstract

Mutual diffusion in aqueous solution of polydisperse poly(ethyleneglycol) samples (PEG) was analysed through Gouy interferometry with special attention to the molecular weight and concentration effects. For PEG samples with molecular weight higher than 1000 g mol^-1 the diffusive trend on concentration is justified in thermodynamic terms. The diffusion properties of polydisperse samples and pure oligomers are compared. We emphasise that the refractive index gradient at the diffusion boundary in polydisperse PEG significantly deviates from a Gaussian distribution expected where the PEG monodisperse. The combination of mutual diffusion with literature intradiffusion and activity data allows testing of the Darken equation for each PEG sample. Because of the polydispersity the analysis of the velocity cross correlation coefficients (VCCs) or the distinct diffusion coefficients becomes critical.

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