Unraveling the effect of charge distribution in a polyelectrolyte multilayer nanofiltration membrane on its ion transport properties

Abstract

Polyelectrolyte (PE) multilayer nanofiltration membranes are composite membranes obtained by layer-by-layer (LbL) adsorption/advection of oppositely charged polyelectrolytes. The mass transport properties of such polyelectrolyte multilayer membranes (PEMMs) strongly depend on membrane structural parameters related to the synthetic preparation conditions as well as on the operating conditions. Understanding the relationship between such structural features and transport properties remains a difficult question to answer. We propose a one-dimensional numerical simulation framework solving the Nernst-Planck-Poisson equations for the transport of ions through n electrolyte layers En and n polyelectrolyte layers PEn - coining this pressure (p) driven transport model as pEnPEn. We utilize different EnPEn-architectures of this model to interpret experimental data of new LbL-membranes. The proposed model framework systematically evaluates the impact of the effect of polycation/polyanion architecture with respect to the rejection of symmetric and asymmetric salts. pEnPEn can be tuned to reveal and explain the influence of the ionic crosslinking, charge compensation, and overcompensation. The model enables to formulate an effective charge distribution for different polyelectrolyte multilayer (PEM) structures. As such, the model framework gives insightful details on ion rejection phenomena, yet it will be a prerequisite and will become even more valuable when combined with neural network modeling based on a hybrid data set combining pEnPEn simulations with experimental input parameter.