Microemulsions are exciting systems that are promising as tunable self-assembling templating reaction vessels at the nanoscale. Determination of the nano-structure of microemulsions is, however, not trivial, and there are fundamental questions regarding their design. We were able to reproduce experimental data for an important microemulsion system using coarse grained simulations involving relatively limited computational costs. The simulation allow visualization and deeper investigation of controversial phenomena such as bicontinuity and ion mobility.
Dense microemulsions of Sodium-AOT/n-heptane/water were simulated using the Martini coarse-grained force field. Sodium-AOT was parameterized by matching the geometry with atomistic simulations. All simulations were based on 800 surfactant molecules in a constant ratio equal to two with oil, while the water content was varied up to 60% in weight. Simulations were 1 us long. From Mean Square Displacement calculation of all species, it was possible to quantify caging effects and ion mobilities. Average diffusion coefficients were calculated for all charged species and conductivity was found in quantitative agreement with experimental data. The scattering function was calculated for the hydrophilic species and matched the experimental data obtained from Small Angle X-ray Scattering measurements. In particular, bicontinuity of water and oil was for the first time computationally visualized. Equilibrated coarse grain simulations were reversed to atomistic models in order both to compare ion mobility and to catch finer simulation details.
e.negro@tudelft.nl
