A mesoscopic simulation method for predicting the rheology of semi-dilute wormlike micellar solutions

We present a fast pointer simulation method that extends the model of Cates and coworkers for the rheology of entangled wormlike micelles. Our method includes not only reptation, breakage/rejoining, contour length fluctuations, and Rouse modes, which were included in Cates' model, but also constraint release, bending modes, and a cross-over to the tight entanglement regime, which had not been previously considered. Our method also contains correlations in micelle length across multiple breakage/rejoining cycles, not included in previous approaches. Our method uses pointers that track the ends of unrelaxed regions along each micelle, thereby allowing efficient simulations of relaxation dynamics for ensembles containing thousands of micelles, to obtain accurate results without preaveraging or neglecting correlations. A modified genetic algorithm is applied to transform the simulation data from the time to the frequency domain. The method can span several regimes of behavior depending on the relative rates of reptation, contour length fluctuations, breakage/rejoining, and high frequency modes and is suitable for predicting the rheological behavior of experimental solutions for wormlike micelles. This new simulation method allows extraction of multiple micellar parameters simultaneously by fitting experimental rheology data across the entire available frequency range. Values of average micelle length and breakage rate thereby obtained can be an order of magnitude different from previous estimates based on local frequency dependencies predicted by Cates' model. These differences are due to more complete physics included in our method and the fitting of G ' and G '' data across the entire frequency range. We also provide quantitative relationships between these parameters and rheological behaviors that improve on previous simple scaling results. (C) 2014 The Society of Rheology.