Diffusion of Poly(ethylene oxide) Chains in Gelling and Nongelling Aqueous Mixtures of Ethyl(hydroxyethyl)cellulose and a Surfactant by Pulsed Field Gradient NMR

Abstract

Tracer diffusion of poly(ethylene oxide) (PEO) in solutions and gels of ethyl(hydroxyethyl)cellulose (EHEC) in the presence of different amounts of the anionic surfactant sodium dodecyl sulfate (SDS) has been studied with the aid of pulsed field gradient NMR. The decay of the spin−echo function exhibits a single-exponential profile. The results suggest that the diffusion of the PEO chains decreases as the matrix concentration increases, while the thermoreversible gelation process does not seem to affect the tracer diffusion rate significantly. The observed obstruction effects registered by the probe molecules depend on the concentration of the matrix polymer (EHEC) and surfactant concentration, but not on the molecular weight of the probe polymer. In the absence of EHEC, the interaction between PEO and SDS gives rise to a gradual expansion of the coil dimensions as the level of surfactant addition increases. The profile of the spin−echo attenuation, obtained from self-diffusion of the matrix polymer, exhibits a more complex behavior than that of the tracer, with initially a stretched exponential (“fast” diffusion) followed by a single exponential (“slow” diffusion) decay.