3D printing highly efficient ion-exchange materials via a polyelectrolyte microphase separation strategy

Ion-exchange materials are commonly composed of polyelectrolyte networks in which crosslinking preserves macroscopic geometry and prevents dissolution in aqueous conditions. However, crosslinking inherently inhibits efficient swelling and mass transfer during ion-exchange processes. Herein, a one-step polymerization-induced microphase separation (PIMS) approach directly using water and linear polystyrene sulfonate macromolecular chain transfer agents (macroCTAs) is developed to engineer bicontinuous nanostructured materials with rapid ion-exchange capabilities. These materials feature water-swollen liquid-like polyelectrolyte domain embedded in a rigid polymer network, where the domain spacing, as determined by small angle X-ray scattering experiments, is precisely modulated between 15 and 89 nm based on the molecular weight of the macroCTA used. As the bicontinuous nanostructure enables rapid mass transfer throughout the material bulk, the 3D printed PIMS materials are able to rapidly remove model charged dyes from solution, exhibiting a mass transfer coefficient ≈35 times higher than commercially available counterparts. This work is the first example demonstrating direct self-assembly of water into continuous nanochannels in a well-controlled manner as supported by time-resolved small-angle neutron scattering experiments during polymerization. Moreover, these nanostructured materials are readily produced using commercially available 3D printers, enabling unparalleled high-resolution fabrication of targeted complex structures, including accurately controllable macroporous geometries and surface areas.