Flow of entangled wormlike micellar fluids: Mesoscopic simulations, rheology and -PIV experiments

There is a great need for understanding the relationship between the structure and chemistry of surfactants forming wormlike micelles, and heir macroscopic flow properties. Available macroscopic Rheological Equations of State (REoS) are often inadequate to predict flow behaviour in omplex geometries or even to describe the full set of rheological measurements. In this paper, we show how the link between surfactant structure nd rheology can be explored through the use of mesoscopic particulate simulations. We describe the development of a realistic Brownian Dynamics odel, where the persistence length of the micelle is the smallest length scale. Most of the parameters for the BD model are obtained from atomistic olecular Dynamics simulations to establish the link to the chemistry of the surfactant. As a preliminary result, we calculate the shear viscosity f a solution of entangled wormlike micelles as a function of increasing shear rate. The results can be approximately mapped on an experimental ow curve for this particular system, using a mean field scaling relationship. Finally, as our motivation in this work is to understand the flow of ormlike micellar fluids in porous media, we give preliminary experimental results for the flow in an expansion-contraction capillary using micro article Image Velocimetry ( -PIV). This demonstrates the complex response of these fluids in non-viscometric flows and the challenges they pose o any predictive simulation model. 2006 Elsevier B.V. All rights reserved.