Electropolymerization of pyrrole on PAN-based carbon fibers: Experimental observations and a multiscale modeling approach

Aqueous electropolymerization of pyrrole on PAN-based carbon fibers has been investigated. Using experimental data obtained from gravimetric analysis and scanning electron microscopy (SEM), a continuum-level electrokinetic-diffusion model has been developed. For short time, the coating process is reaction-limited. Consequently the weight gain increases linearly with time. However, as the reaction time is increased, the weight gain becomes proportional to the square root of time suggesting that diffusion of the monomer onto the reactive sites of the growing aggregates becomes the controlling mechanism. These observations motivated a multiscale approach for the simulation of mesoscopic coating morphology in a model process where the monomers diffuse to a heterogeneous surface that consists of growing surface-bound polymetric chains with reacting ends. A diffusion-limited, aggregation (DLA)-based approach is used to derive transition probabilities consistent with continuum-level conservation principles and used in lattice Monte Carlo simulations. This approach is illustrated for two-dimensional lattices. The scaling laws obtained for this process such as the thickness of the coating as a function of the number of particles are compared with those for classical DLA. The influence of effective diffusion coefficient and reaction rate constant on the surface coverage, maximum and bulk values of coating density, as well as the boundary layer thickness, is examined in detail.