Effect of Flow on Charge Transport in Semi-Dilute Redox Active Polymer Solutions

Redox-active polymers (RAPs) are a subset of polyelectrolytes possessing the ability to store charge and undergo redox self-exchange. These materials have garnered attention in the field of redox flow batteries due to their chemical modularity, molecular size, and ability to rapidly charge and discharge. Although their modularity is an opportunity to design at the molecular level for efficient charge transport, this would require a fundamental understanding of how RAP dynamics are coupled to charge transport in redox flow batteries. Previous work has explored the charge transport mechanisms and how they are affected by hydrodynamic interactions in equilibrium. We now seek to understand how flow and subsequently non-equilibrium RAP conformations give rise to charge transport; specifically when chain-to-chain interactions exist.We use Brownian Dynamics simulations paired with a Monte Carlo representation of charge-hopping to model charge transport in flowing solutions, using a 'conformational averaging' technique to account for hydrodynamic interactions. This model is used to show how polymer extension in strong flows give rise to modified charge transport both between chains and within the same chain. Furthermore, this modification depends on the fraction of RAP monomers charged. RAPs with a low fraction of charges show increases in charge transport with flow, while highly charged chains show decreases in charge transport with flow due to the limited amount of accessible hopping sites.