DIFFUSION OF POLY(ETHYLENE OXIDE) CHAINS IN GELLING AND NONGELLING AQUEOUS MIXTURES OF ETHYL(HYDROXYETHYL)CELLULOSE AND A SURFACTANT BY PULSED-FIELD GRADIENT NMR

Tracer diffusion of poly(ethylene oxide) (PEO) in solutions and gels o f ethyl(hydroxyethyl)cellulose (EHEC) in the presence of different amo unts of the anionic surfactant sodium dodecyl sulfate (SDS) has been s tudied with the aid of pulsed field gradient NMR. The decay of the spi n-echo function exhibits a single-exponential profile. The results sug gest that the diffusion of the PEO chains decreases as the matrix conc entration increases, while the thermoreversible gelation process does not seem to affect the tracer diffusion rate significantly. The observ ed obstruction effects registered by the probe molecules depend on the concentration of the matrix polymer (EHEC) and surfactant concentrati on, but not on the molecular weight of the probe polymer. In the absen ce of EHEC, the interaction between PEO and SDS gives rise to a gradua l expansion of the coil dimensions as the level of surfactant addition increases. The profile of the spin-echo attenuation, obtained from se lf-diffusion of the matrix polymer, exhibits a more complex behavior t han that of the tracer, with initially a stretched exponential (''fast '' diffusion) followed by a single exponential (''slow'' diffusion) de cay.