Due to their superior chemical stability, charged hydrocarbon polymers have shown promise for desalination applications. Charged polymers most often contain strongly acidic or strongly basic functional groups that render the polymer hydrophilic, but the presence of the charged functional groups also has a strong impact on the transport properties of ions through the polymer. In this work, fundamental sodium chloride sorption and transport studies have been performed in order to develop structure/property relationships to help guide the development of high performance materials for desalination.The transport of sodium chloride through various positively and negatively charged membranes has been examined by means of chemically driven (ion sorption, salt permeability) and field driven (electrical resistance, conductivity) processes.Ion sorption and salt permeability data were used to extract information about the bulk diffusion of salt in a charged membrane within the framework of the solution-diffusion model, where the salt permeability is equal to the product of the mobile salt sorption coefficient and the bulk salt diffusion coefficient, Ps=KsDs. The concentration of ions in the membrane was measured by extracting the ions through a desorption technique, followed by subsequent analysis of the solution for the ion content using ion chromatography or flame atomic absorption spectroscopy.In order to gain insight about the individual ion diffusion through the membrane, the salt permeability data were used in conjuncture with electrical conductivity data, assuming the validity of the Nernst-Einstein relationship, which states that the individual ion mobility is directly proportional to the ionic diffusion coefficient. The specific electrical conductivity of the membranes was measured using electrochemical impedance spectroscopy. The feasibility of using information from chemically driven and field driven processes in order to shed light on the diffusion of individual ions through a charged polymer matrix is discussed.

Ion sorption and transport in ion-exchange membranes

248th National Meeting (2014)

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