(317f) Stimuli-Responsive Charge Mosaic Membranes Prepared Using Layer-By-Layer Assembly

Charge mosaic membranes (CMMs) are capable of separating dissolved ions from neutral molecules of comparable size by facilitating diffusion of charged species through oppositely charged domains. We have developed a new class of the CMMs by utilizing layer-by-layer assembly to form positively and negatively charged polymeric nanotubes. Selecting different polyelectrolyte multilayer systems determines the nanotube functionality. These nanotubes are vertically aligned and traverse the membrane thickness with no overlap of adjacent charged domains. Initial studiesrevealed these CMMs have hydraulic permeabilites of 8 L m^–2 hr^–1 bar^–1. Since the charge mosaic membranes are fabricated from polyelectrolyte multilayer systems, they exhibit greater functionality and stimuli-responsiveness than CMMs fabricated from other materials (e.g., ion exchange resins). In particular, our CMMs demonstrate a pH-induced hysteresis in both pure water flux and salt rejection. Using profilometry and Fourier transform infrared spectroscopy, we identify that the hysteresis is a result of the polymer nanotubes swelling and deswelling as the functional groups are protonated and deprotonated. Challenging the membrane with feed solutions of varying ionic strength and feed component chemistries illuminated some of the underlying transport mechanisms of the CMMs. These properties demonstrate the increased functionality of these novel CMMs as a result of fabrication from layer-by-layer assembly of polyelectrolytes.