Interplay between structure and shear flow in micelle-nanoparticle solutions*

Cationic surfactant molecules exhibit rich phase behavior in water. Self-assembly results in spherical, cylindrical and flexible wormlike structures with or without branches. We employ molecular dynamics simulations to study the structure and rheology of self-assembled aggregates of cetyltrimethylammonium chloride surfactants in presence of sodium salicylate counter ions in aqueous solution. Addition of nanoparticles (NPs) to such solutions results in the formation of electrostatically stabilized NP-micelle junctions, leading to a significant increase in the solution viscosity. Distinct rheological properties are observed by changing the surfactant, co-surfactant as well as NP concentrations. Micelle branching causes the solution viscosity to vary as a non-monotonic function of the NP concentration. At higher NP volume fractions and shear rates that exceed the inverse of a characteristic structure relaxation time, flow-alignment of the microstructure causes pronounced shear thinning [Molecular Simulation: http://www.tandfonline.com/doi/abs/10.1080/08927022.2017.1387658]