Specific salt effects on equilibrium and flow structure of wormlike micelles

Abstract: Adding a dissolved salt to aqueous solutions of surfactant molecules is a well-understood method of altering how the molecules self-assemble into micelles. In a certain range of salt and surfactant concentrations, the most energetically favorable micelle shape is a long, flexible cylindrical micelle referred to as a ‘wormlike’ micelle. In this work, we show that a variety of simple salts can be used to independently control the contour length and persistence length (stiffness) of a model wormlike micelle system. Static neutron scattering was used to determine the micelle persistence length, and RheoSANS measurement are used to measure the segmental alignment of the micelles under shear flow conditions. We also develop a semi-empirical model to explain the relative importance of micelle stiffness, micelle length, and degree of entanglement on the onset of segmental alignment in these systems, and gain further insight into the fundamental physics of wormlike micelle solutions.