INTERACTIONS BETWEEN POLY(ETHYLENE OXIDE) AND SODIUM DODECYL-SULFATE AS STUDIED BY NMR, CONDUCTIVITY, AND VISCOSITY AT 283.1-298.1 K

The aggregation of sodium dodecyl sulfate (SDS) in aqueous solution co ntaining a constant amount of poly(ethylene oxide) (PEG) at 2000 ppm h as been investigated by several experimental techniques at three tempe ratures, 298.1, 288.1, and 283.1 K. The techniques include conductivit y, viscosity, NMR self-diffusion, NMR chemical shift, and NMR relaxati on. The critical aggregation concentration of SDS on the polymer stran d (cac) as well as the concentration where ordinary micelles start for ming (c(2)) has been determined. There are some inconsistencies in the data due to different measuring techniques. However, techniques that basically monitor the SDS molecules, for instance conductivity and SDS -sensitive NMR techniques, provide cac values that are consistent. Abo ve the cac the concentration of free SDS monomers will increase in par allel to the aggregation process. At c(2) ordinary micelles will form, and in the concentration range of about 15-25 mmolal the SDS molecule s will aggregate as normal micelles or in aggregates on the polymer, a nd these processes run in parallel. A crude calculation of the Gibbs' energy of the two aggregation processes suggests that the energetics o f the two processes are of similar magnitude, and thus consistent with observation. (C) 1998 Academic Press.