A pulsed field gradient NMR study of poly(oxyethylene) diffusion in aqueous solutions and gels of ethyl (hydroxyethyl) cellulose-sodium dodecyl sulphate systems

The tracer diffusion of poly(oxyethylene) (POE) with molecular weights (M) of 120 000 and 963 000, respectively, in an aqueous polymer matrix composed of ethyl (hydroxyethyl) cellulose (EHEC) and the anionic surfactant sodium dodecyl sulphate (SDS) has been studied using pulsed field gradient spin-e cho (PGSE) NMR. The tracer diffusion of POE has been studied in both the so l and gel states, which appear at elevated temperatures, for a number of ma trix concentrations in the range 1-4 wt.%. The SDS concentration was kept c onstant at 4 mmolal. Time-resolved PGSE experiments show that in general th e tracer diffusion of POE chains with M = 120 000 is Fickian, except at the highest matrix concentration in the gel state, where non-Fickian diffusion is detected. For the POE tracer with M = 963 000 the diffusion in the sol state gradually departs from Fickian diffusion and becomes anomalous as the matrix concentration increases. In the gel state, anomalous diffusion is o bserved at matrix concentrations above 1 wt.%. Obstruction effects are dete rmined for the two different tracer chains in the sol state as a function o f the matrix concentration. At 1 wt.% EHEC, obstruction effects increase wi th tracer molecular weight. At higher matrix concentrations, these effects are found to be nearly identical. (C) 1999 Elsevier Science B.V. All rights reserved.