Electromotive force studies associated with the binding of sodium dodecyl sulfate to a range of nonionic polymers

The interaction between sodium dodecyl sulfate (SDS) and a variety of nonionic polymers has been studied using an SDS membrane selective electrode. From the experimental data critical concentrations associated with the binding process have been evaluated. These are (I) the onset of binding T-1, (II) the SDS concentration T-2 corresponding to the polymer becoming "saturated" with bound SDS, and (III) the SDS concentration (T-f) when free micelles occur in solution. The binding isotherms have also been measured at different added salt concentrations and in some cases different molecular weight polymers. At low salt concentration the different polymers show some selectivity toward SDS in the sense that the maximum amount of SDS they can bind per gram varies from polymer to polymer. However, in the presence of added salt, this selectivity is almost removed and all polymers seem to behave in a similar fashion. The presence of free sodium counterions in solution whether generated as a result of low counterion binding by the bound surfactant or by simply adding salt also governs the concentrations at which free micelles occur in solution.