Electromotive force and isothermal titration microcalorimetry measurements have been carried out to study the interactions of sodium dodecyl sulfate (SDS) with polyethyleneimines (PEI's) and some ethoxylated PEI's at different pH's. In all cases the polymers show a remarkable affinity toward SDS. The SDS concentration at the onset of binding decreases with decreasing pH. At low pH's phase separation similar to that observed for strong polyelectrolyte/oppositely charged surfactant systems occurs presumably as a consequence of the protonation of the N atoms in the polymer to form a polycation. The SDS range over which phase separation occurs decreases as the size of the ethoxylated chains increases, and for the polymer with the longest ethoxylated chain no precipitation occurs. In many cases where phase separation occurs, as more SDS is added the polymer/surfactant complex often resolubilizes and binding proceeds until the polymer becomes saturated with bound SDS. For any given polymer at this limiting stage in the binding, the number of surfactant molecules bound per mole of polymer is independent of pH. In addition both the charged and uncharged N atoms as well as the pendant ethoxylated chains make significant contributions to the binding process.

The interaction between the dendrimers poly(1,4-diaminobutane) DAB n (n = 8, 16, 32, 64) and poly(pyrrolidone-1,4-diaminobutane) DAB n Py (n = 8, 16, 32) with the surfactants sodium dodecyl sulfate (SDS), tetradecyltrimethylammonium bromide (TTAB), and hexaethyleneglycol monododecyl ether (C12EO6) have been studied using electromotive force (EMF) measurements involving a surfactant-selective electrode and also isothermal titration microcalorimetry (ITC). The EMF data shows apparent binding of SDS to all the dendrimers at SDS concentrations lower than 10-5 mol dm-3. As more SDS is added, the binding process continues until the dendrimer becomes fully saturated with bound SDS, at which point the EMF and ITC data for SDS solutions with and without the dendrimers merge. At low SDS concentrations the binding mechanism is a noncooperative process driven by hydrophobic interactions between the hydrocarbon chains in the cavity of the dendrimer and also electrostatic attraction between the surfactant headgroups and the mildly cationic nitrogen atoms in the inner core of the dendrimer. As binding proceeds, there is a gradual transition to a cooperative binding process in which micellar-type bound SDS aggregates are formed on the dendrimers. This continues until the dendrimer can no longer bind any further surfactant which signals the occurrence of free regular SDS micelles in solution. The binding between SDS micelles and the dendrimers is driven by primary electrostatic interactions which also promote stable micellar bound SDS aggregates. C12EO6 shows a limited amount of binding to some of the dendrimers, although the binding is noncooperative, driven by hydrophobic interactions between the surfactant and the internal cavity of the dendrimer. TTABr was only found to show a very small interaction with DAB16 at a high dendrimer concentration.

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 T1, (II) the SDS concentration T2 corresponding to the polymer becoming "saturated" with bound SDS, and (III) the SDS concentration (Tf) 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.