Redox-active polymers (RAPs) have pendant groups that can change their charge state due to an electrochemical driving force. There has been an interest in using RAPs as a charge storage medium in redox flow batteries due to their ability to take on charge combined with their large macromolecular size. The performance of these batteries is in part tied to the transport of charge within these RAP solutions, and consequently there has been a recent effort to understand the physics governing charge diffusion in RAP systems. These efforts have highlighted the key role of both intra- and intermolecular charge transport mechanisms in governing their electrochemical response; however, little is known about how the molecular structure of polyelectrolyte solutions affects these proposed mechanisms. In this paper, we develop a coarse-grained, hybrid Brownian dynamics and kinetic Monte Carlo simulation to study charge transport in RAP solutions. We show how a number of different transport mechanisms interplay, including the intrapolymer transport of charge both along the chain via self-exchange transport and polymer segmental motions as well as hopping due to interpolymer collisions and translational diffusion of the chains themselves. We provide theoretical arguments to describe the diffusive motion of charge via these mechanisms, which match well with simulation results. Our predictions suggest the existence of three distinct regimes of charge transport, which distinguish between inter- and intramolecular processes and dilute and semidilute solutions.

The breakage of an agglomerate of wet flexible fibers impacting a plane is computationally investigated in this work using the discrete element method. In the agglomerate, the fibers stick together due to cohesive liquid bridge forces. Agglomerate breakage with various impact conditions, initial configurations, fiber properties, and liquid bridge properties is systematically investigated. The degree of breakage is governed by the impact energy, the cohesion energy due to liquid bridges, the energy dissipation/absorption through fiber-fiber contacts and fiber deformation, and the efficiency of force transmission within the agglomerate. More specifically, breakage is promoted by increasing impact velocity, decreasing agglomerate size, increasing initial compaction, increasing fiber bending modulus, decreasing liquid surface tension, and decreasing liquid-to-solid volume ratio. Breakage is strongly dependent on the modified Weber number, that is, the ratio of the Weber number to a dimensionless rupture distance, which is a measure of the impact energy relative to the cohesion energy. K E Y W O R D Sagglomerate breakage, discrete element method, flexible fiber, liquid bridge force