Shear Induced Transitions in Mixed Surfactant Systems

The non-equilibrium phenomena under shear observed mainly in bilayer forming liquid crystalline phases of mixed surfactant systems, dispersions as well as Langmuir monolayers of membrane peptides. To correlate the structural transitions under shear with the mechanical properties or flow behaviour, the rheological measurements are combined with different techniques such as optical imaging (bright field, polarizing or confocal), small angle light scattering as well as small angle x-ray scattering (Rheo-SAXS) measurements. The bilayer forming phases that have been studied consist of mixed surfactant system formed by a mixture of ionic amphiphiles with strong binding organic counter ions. The main motivation is to examine the stability of these phases under shear since all the existing studies so far on shear induced structural transitions are mainly confined to highly swollen isotropic sponge phase of interconnecting bilayers that can transform to a lamellar phase consisting of a stack of bilayers with 1D quasi long range order or a dilute lamellar phase is shear transformed to a collapsed surfactant rich lamellar phase coexisting with excess solvent at Peclet Number greater than 1.