Molecular dynamics in dilute aqueous solutions of ethyl(hydroxyethyl)cellulose and sodium dodecyl sulfate as investigated by proton NMR relaxation

Dilute aqueous solutions of ethyl(hydroxyethyl)cellulose (EHEC) and sodium dodecyl sulfate (SDS) have been investigated by H-1 NMR shift and relaxation measurements. The shift measurements indicate no presence of EHEC at the core of the SDS micelles but at and just inside the micellar surface. Both the spin-lattice relaxation time (T-1) and the spin-spin relaxation time (T-2) imply that molecular motions slow as the system aggregates. T-1 measured at both 270 and 400 MHz indicates nonextreme narrowing conditions with molecular motions on the nanosecond time scale. T-2 monitors slower dynamics of the EHEC/SDS/ water as compared to both of the systems polyethylene oxide (PEO)/SDS/water and SDS/water, attributed to the rigid EHEC backbone as compared to the more flexible PEO chain. An important observation is that the NMR relaxation data correlate well with the microviscosity in the EHEC/SDS/water system as measured by intramolecular excimer formation of the fluorescent probe 1,3-di(1-pyrenyl)propane (P3P).