(211d) Brownian Dynamics Simulation of Dilute Wormlike Micelle Solutions

Rodlike and wormlike micelles are formed by self-assembly of surfactant monomers under certain surfactant and salt concentrations. Imposition of flow can lead to diverse rheological behavior including shear thinning and shear thickening via the formation of flow-induced structures. It has been shown experimentally that macroscopic flow phenomena are intricately tied to the underlying anisotropic microstructure evolution. Therefore understanding the microstructural dynamics is crucial in order to explain the observed macroscopic properties.

Atomistic and coarse grained molecular dynamics simulations that take into account solvent/salt mediated interactions have limitations since the time scales accessible by these simulations are much shorter than relevant flow timescales. Therefore, it is essential to develop coarse-grained mesoscopic models for such systems in order to study microstructure evolution under flow conditions.

We present a self-consistent, coarse-grained model for describing the mesoscopic dynamics of dilute wormlike micellar solutions subjected to flow deformation. The proposed model is applicable in the regime where the time scale of scission/combination reactions is much greater than the flow time and accounts for the effects of micelle length and charge on solution rheology. Solvent mediated intra-micellar interactions which depend on surfactant and salt concentration are also incorporated. The configurational and rheological properties of CTAB micelles in NaBr and KBr are investigated via the Brownian dynamics approach. The effect of inclusion of electrostatic interactions on rheological properties is presented under steady shear and uniaxial extension. Microstructure evolution is also analyzed to explain the observed changes in macroscopic properties and their scaling with the flow rate.