Ion transport in weak polyelectrolyte membranes at varying external pH

Charged polymer membranes are of great interest in various applications, ranging from environment, energy, and health. Understanding of ion transport in charged polymer membranes is critical to the advancement of technologies related to polymer electrolytes in batteries, water purification, critical element extraction, environmental remediation, and medical isotope purification. Here, we designed a systematic library of weak polyelectrolyte membranes based on polyacrylic acid (PAA). A series of polyacrylic acid (PAA) based polymer networks were synthesized with varied charged group contents and controlled water swelling. By adjusting external pH, the number of sodium counter cations dissociated and condensed on the polymer backbone can be systematically changed, leading to different ion transport and dielectric properties in the polymers. We evaluated ion and water transport properties (solubility, diffusivity, and permeability) in the resultant polymer membranes. These transport properties are correlated with dielectric properties in the polymers via dielectric relaxation spectroscopy (DRS). This model system enables us to elucidate the mechanism of ion transport in charged polymer membranes.