Coarse grained molecular dynamics (MD) simulations are used to study equilibrium structure as well as shear-induced structure changes and rheology of cationic cylindrical micelles of Cetyl-trimethyl ammonium chloride (CTAC) solutions. These simulations extend of our earlier work [1-2] which was limited to studying single micelle dynamics and binary micelle interactions. In the current work, systems that consist of O(100) cylindrical micelles are simulated in presence of explicit solvent and salt (NaSal) interactions. Utilizing an algorithm that tracks the direction of the maximum density of the head groups, we evaluate the micelle contours and orientation correlations from which micelle lengths, persistence length and shape anisotropy are calculated as functions of salt concentration. Probability distribution function (pdf) of micelle length is found to be an exponential function for an equimolar ratio of salt to surfactant ratio, consistent with theoretical predictions [3]. However, a log normal pdf is observed for lower salt to surfactant concentration ratio. The average micelle length for a given surfactant concentration increases sub-linearly with a power law exponent of 0.4. By varying the salt and surfactant concentration a phase diagram that consists of dilute, semi-dilute and entangled systems is obtained. Non-equilibrium MD simulations are performed to understand the molecular mechanisms underlying the phenomenon of shear-induced structure (SIS) formation in observed in cylindrical micelle solutions. This and the effect of nanoparticle addition on structure and rheology of micelle networks will be discussed.1. A.V. Sangwai & R. Sureshkumar, Langmuir, 27, 6628 (2011)2. A.V. Sangwai & R. Sureshkumar, Langmuir, 28, 1127 (2012)3. M.E. Cates & S.J. Candau, J. Phys.: Condens. Matter 2, 6869 (1990)Support through NSF CDI Grant PHY 1049489 is gratefully acknowledged.

Structure and rheology of micelle and micelle-nanoparticle solutions from molecular dynamics simulations

247th National Meeting (2014)

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