Elongational flow of solutions containing poly(ethylene oxide)/sodium dodecyl sulfate complexes in the presence of n-alkanols

The effect of the presence of n-alkanols on the extensional rheology of solutions containing polymer/surfactant complexes has been investigated experimentally in an opposed-jets device. Aqueous solutions of high-molecular-weight poly(ethylene oxide) (PEO) and sodium dodecyl sulfate (SDS) exhibit an extension thickening behavior that is stronger than that of the pure polymer solution because of the formation of micellar aggregates of SDS along the PEO chain that promote intermolecular interactions between polymer chains. The addition of a short-chain alcohol (ethanol) affects the rheology of PEO/SDS solutions by changing the solvency characteristics of both PEO and SDS. Adding ethanol to water decreases the quality of the solvent for PEO, which promotes intermolecular interactions between polymer chains and strengthens extension thickening in semi-dilute PEO/water/ethanol mixtures. On the other hand, high enough concentrations of ethanol dissolve the SDS micellar aggregates, eliminating their influence on extension thickening. Long-chain alcohols (n-octanol) substantially enhance extension thickening effects. The presence of n-octanol lowers the critical aggregation concentration for the formation of SDS micellar aggregates along the PEO chain and promotes intermolecular interactions at PEO concentrations that would not exhibit extension thickening without n-octanol.