Network formation in polyethyleneglycol solutions. An intradiffusion study

Intradiffusion coefficients of binary mixtures, water-polyethyleneglycol (P EG) (molecular weight 200, 400, 2000, 3400, 10000 Da), were measured by pul sed gradient spin echo (PGSE)-NMR to determine the mass and concentration e ffects. The properties of polydisperse samples are compared with those of o ligomers, and the effect of polydispersity is discussed. The PEG diffusion coefficients approach a constant value at high concentration, indicating th e formation of a dynamic network between water and PEG molecules. The stoch iometry of this network is evaluated and compared with the result of a mode l derived from an extension of gelation theory. It was found that at infini te dilution limiting self and mutual diffusion coefficients are not equal: this has been interpreted as an effect of polydispersity.