MODELING APPROACHES IN ELECTROPHORETIC DEPOSITION

Electrophoretic deposition (EPD) occurs when electric-field-driven colloidal particles suspended in a fluid migrate toward an electrode or liquid−liquid interface where they assemble into a deposit. The deposition rate depends on many parameters, such as the applied field strength, volume fraction of colloids, and electrophoretic mobility. Enhanced control of the shape, composition, and performance of functional materials fabricated via EPD can benefit from computationally feasible models that predict transient formation and resulting morphology of colloidal depositions. Here we discuss a broad range of EPD modeling approaches, their applicability and predictive capabilities. The majority of available models provide continuum level descriptions of EPD [1] that inherently neglect inter-colloidal interactions. Such models predict mass deposition rates that depend (at least) on the electrophoretic velocity, electrode surface area, and fraction of colloids that stick to the deposit. Film thickness models suggest nonuniform deposits occur when the colloidal particle permittivity exceeds that of the suspension or near electrode edges where electric field singularities locally enhance deposition rates. Alternative particle level modeling of EPD is still nascent, but promises to offer more detailed predictive information about deposit formation and packing morphology than traditional approaches. To this end, we also present and evaluate a particle-based model of colloidal suspensions that undergo electrophoretic motion and deposition [2] using an extensive set of mesoscale simulations that characterize experimentally relevant colloidal suspensions. Since the model explicitly computes inter-colloidal interactions, it is uniquely poised to elucidate how deposition conditions influence defect structures and particle rearrangement within EPD colloidal crystals. We use the model to investigate how empirical parameters, such as electric field strength and electrolyte concentration, can be tuned in order to control the degree of colloidal ordering versus non-ordering that occurs during EPD. It is straightforward to configure the model to study how various preparations of the interface, e.g. a bare surface, a lattice of particles, an amorphous monolayer, etc., and also annealing schemes influence the deposit microstructure. [1] Ferrari, B.; Moreno, R. EPD Kinetics: A Review. Journal of European Ceramic Society. 2010 (5), pp 1069-1078. [2] Giera, B.; Zepeda-Ruiz, L. A.; Pascall, A. J.; Weisgraber, T. H. Mesoscale Particle-Based Model of Electrophoretic Deposition. Langmuir. 10.1021/acs.langmuir.6b04010 This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA2734