Hosted by: Chang-Yong Nam

Membrane-based technologies are energy efficient and have a small footprint, making them economically attractive candidates to help address our water and energy needs. Ion exchange membranes (i.e., charged membranes, ionomers, etc.) are critical for efficient operation of a number of membrane-based technologies such as electrodialysis, reverse electrodialysis, fuel cells, etc., due to their ability to effectively control rates of water and ion transport. Efforts are also underway to harness their separation properties for applications that have not traditionally used them (e.g., reverse osmosis, pressure retarded osmosis, etc.). One avenue for improving these technologies is to develop more effective membranes. Rational design of high performance membranes could be catalyzed by fundamental knowledge of the connection between polymer structure (physical or chemical) and transport properties. However, despite the long history of literature on the topic and the industrial importance of such materials, the current state of understanding is incomplete. Experimental techniques for characterizing ion sorption and transport in charged membranes have been established, however, a simple theoretical framework for interpreting the experimental findings is missing. In this study, a framework for ion sorption and diffusion in charged membranes based upon ideas from polyelectrolyte theory (e.g., counter-ion condensation) has been formulated and tested against experimental data. For the membranes considered in this study, the framework accurately described, and in some cases predicted, concentration gradient (i.e., salt permeability) and electric field (i.e., ionic conductivity) driven ion transport. The main factors governing ion sorption and transport in charged polymers are discussed. Our long-term goal is to use such knowledge to establish structure/property relations leading to rational design of membranes with improved performance.