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

Mutual diffusion in aqueous solution of polydisperse poly(ethyleneglycol) s amples (PEG) was analysed through Gouy interferometry with special attentio n to the molecular weight and concentration effects. For PEG samples with m olecular weight higher than 1000 g mol(-1) the diffusive trend on concentra tion is justified in thermodynamic terms. The diffusion properties of polyd isperse samples and pure oligomers are compared. We emphasise that the refr active index gradient at the diffusion boundary in polydisperse PEG signifi cantly deviates from a Gaussian distribution expected where the PEG monodis perse. The combination of mutual diffusion with literature intradiffusion a nd activity data allows testing of the Darken equation for each PEG sample. Because of the polydispersity the analysis of the velocity cross correlati on coefficients (VCCs) or the distinct diffusion coefficients becomes criti cal.