We present a systematic coarse grained molecular dynamics (MD) study of the structure, dynamics and rheology of cationic micellar solutions in the presence of explicit solvent and highly binding organic salt. The simulations are capable of accurately predicting shape transitions, binary interactions, shear-induced configurational dynamics and anomalous viscosity variations as a function of salt concentration observed experimentally in such systems [1-4]. We simulate systems that contain up to a million beads, and access microsecond timescales, while still preserving the underlying physical chemistry. For the first time, estimates of micelle size distribution, persistence length, end-cap energy and recombination time are obtained directly from MD simulations. Effect of counterions on the dynamics and energetics of wormlike micelles under uniaxial extensional flow will be presented. Specifically, two mechanisms will be discussed: (i) counter ion-induced stiffening of rodlike micelles, and (ii) energy redistribution along the micelle contour caused by flow-induced advection of counter ions leading to mid-plane scission of the micelle. The addition of nanoparticles (NPs) to wormlike micellar fluids is shown to result in the formation of electrostatically stabilized junctions. Effect of NP volume fraction on the equilibrium structure and shear rheology of such solutions will be discussed. Non-equilibrium MD simulations of such mixtures exhibiting complex rheological behavior including shear thinning, shear thickening and shear-induced isotropic to nematic transition will also be presented.<br/>Acknowledgements: The authors gratefully acknowledge NSF grants No. CBET-1049454 and No. CBET-1049489 for partial support of this research. This work used the computational resources provided by Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by NSF grant number OCI-1053575.<br/>[1] A. V. Sangwai and R. Sureshkumar, Langmuir 27, 6628 (2011). [2] A. V. Sangwai and R. Sureshkumar, Langmuir 28, 1127 (2012). [3] A. Sambasivam, A. V. Sangwai, and R. Sureshkumar, Phys. Rev. Lett. 114, 158302 (2015). [4] S. Dhakal and R. Sureshkumar, J. Chem. Phys. 143, 11, 024905 (2015).

Molecular dynamics simulations of micelle and micelle-nanoparticle solutions: Structure, dynamics, and rheology

251st National Meeting (2016)

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