Surfactants are amphiphillic molecules with a hydrophilic head group and a hydrophobic tail. Above a critical concentration, known as the critical micellar concentration they are known to self assemble into a variety of structures such as worm like micelles, cylindrical micelles and lamellar sheets. The surfactant microstructure in the solution gives rise to interesting rheological properties making them useful in foods, consumer care products and drilling fluids.

Worm-like micellar (WLM) solutions of cationic surfactants exhibit unusual flow behavior under shear. One of my research interest is to study the formation of shear banding, i.e., the splitting of a viscometric flow into bands of different local shear rates of these solutions. We are further investigating the nonlinear shear rheology of cationic surfactant solutions in conjunction with small angle light scattering (SALS): by using a rheo-SALS instrument (TA instruments) developed in our group at the University of Delaware.

The other aspect of this project is to explore concentrated surfactant solutions where the surfactants crystallize at room temperature. The presence of surfactant crystals is expected to give a paste like texture to the material, rheologically manifested as a solid like behavior at rest and “yielding” under flow. The effect of crystal habit and morphology on the rheological properties of the material is also under investigation.