(661e) Coarse-Grained Models of Structures and Dynamics of Nanoscale Ionic Materials

      Nanoscale ionic materials (NIMs) provide design flexibility in terms of mechanical, optical and thermal properties relative to existing hybrid materials. Composed of ionically modified nanoparticles with large counter ions, NIMs can be engineered to be fluids at room temperature.

      We use coarse-grained molecular dynamics over μs time scales to simulate two NIMs models, tethered by linear counter ions (NIMs-L) and 3-arm star counter ions (NIMs-S), respectively, and one comparative uncharged model (NOHMs). We choose model parameters to match experimental systems. The pair correlation functions show interpenetration of attached-ion layers between cores and close core-counter ion contacts in NIMs-L. Due to steric hinderances and entropy loss, the corresponding feature peaks are greatly diminished or disappear in NIMs-S. Frequent intra- and inter-core hopping are observed, confirming the hypothesis from a recent experiment [ACS Nano 4, 3735-3742, 2010]. Inter-core hopping is also found to be a dominant factor for chain diffusions at time scales longer than ~10 ns. Finally the cores do not exhibit diffusive behavior until after ~ 0.3 μs and the NIMs cores diffuse more slowly than the NOHMs due to the electrostatic interactions.