Polymer-induced wormlike-to-spherical micelle transition in surfactant solutions

Abstract

In various applications important to chemical, pharmaceutical, petroleum, and mineral processing industries, surfactant molecules are present in solution not alone but along with synthetic or biological macromolecules. The presence of polymer molecules gives rise to changes in the solution and its interfacial properties as compared to the corresponding polymer-free systems.The interaction between surfactant and polymer results in association of the two, which affect many properties of the system, especially the rheological ones. Recently, a polymer induced transition from non-Newtonian to Newtonian behavior was observed in the CTAB/NaSal system. This effect was attributed to a polymer-induced break-up of the worm-like micelles into spherical ones. This interpretation can be tested directly by microscopic observation.In this study, interactions between poly(vinylmethylether) (PVME) or poly(propyleneoxide) (PPO) (Aldrich, WI) and the nonionic surfactant pentaethylene glycol mono-dodecyl ether (C12E5) (Nikkol, Japan) or the cationic surfactant cetyltrimethylammonium bromide (CTAB) (Aldrich) with presence of sodium salicylate (NaSal) (Mallinkordt, MO) were examined by cryo-TEM and rheometry.