Interaction of main chain cationic polyelectrolyte with sodium dodecyl sulfate

The interaction of x,y-ionene (x=2,4,6; y=4,6,12) polycations with sodium dodecyl sulfate (SDS) has been investigated in aqueous solution. It was found that there is a narrow molar ratio of SDS/cation (∼1.0–1.35) depending on different ionenes, at which the viscosity of ionene–SDS aqueous solution rises suddenly due to the formation of water soluble inter-polymer aggregates via the SDS attached on the polymer chains. The viscosity falls sharply with further addition of excessive SDS, which forms micelle in solution and causes the de-aggregation of the inter-polymer aggregates. The x, y values of the ionene, the polymer concentration and the SDS/cation ratio play a key role in determining the viscosity behavior. At the higher concentration of ionene a gelation occurs suddenly from solution at a specific molar ratio of SDS/cation and was confirmed to be reversible. The viscosity increase and gel formation in ionene–SDS aqueous solution were considered to be related closely with presence of the hydrophobic domain. Using N,N-dimethylflavon as fluorescent probe, the existence of hydrophobic domain in solution has been verified, the hydrodynamic radius of the aggregates in the viscose solution was determined with laser light scattering and an explanation for the viscosity change as well as the gel formation has been proposed.