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 containing a constant amount of poly(ethylene oxide) (PEG) at 2000 ppm has been investigated by several experimental techniques at three temperatures, 298.1, 288.1, and 283.1 K. The techniques include conductivity, viscosity, NMR self-diffusion, NMR chemical shift, and NMR relaxation. The critical aggregation concentration of SDS on the polymer strand (cac) as well as the concentration where ordinary micelles start forming (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. Above the cac the concentration of free SDS monomers will increase in parallel to the aggregation process. At c(2) ordinary micelles will form, and in the concentration range of about 15-25 mmolal the SDS molecules will aggregate as normal micelles or in aggregates on the polymer, and these processes run in parallel. A crude calculation of the Gibbs' energy of the two aggregation processes suggests that the energetics of the two processes are of similar magnitude, and thus consistent with observation. (C) 1998 Academic Press.