Molecular dynamics is a powerful tool for probing properties of materials that are difficult to study through experimental techniques. One such phenomenon is ion conduction, which occurs through opportunistic hopping from one solvation site to another in the polymer host. We use atomistic molecular dynamics to probe ion behavior in a PEO-based ionomer. In particular, we working towards identifying conditions which enable a new “super-ionic” conduction mechanism utilizing ion aggregations. We are using also coarse-grained techniques to understand the behavior of ion aggregation. In our approach, the polymer is implicitly represented such that our simulation has only ions. These ions interact as if the polymer was present.
We find from our simulation that ion aggregates form string-like random-walks. In general, ions have two oppositely charged neighbors but there are instances of ions which have an extra third neighbor. We find that these extra ions can cascade charge down an ion chain, transferring charge a greater distance than the motion of any particular ion. This may be the mechanism behind the superionic phenomenon found in atomistic simulations.
MD atomistic simulations of polymer melts.
A limitation of atomistic molecular dynamic is that the level of detail makes the computational coasts of driving the simulation expensive for even our most modern computers. Coarse-graining is a simulation technique that allows us to reduce the detail of a simulation so that we can obtain good statistics on a particular phenomenon of interest.