Specific Ion Separations by Controlling the Molecular Environment of Hydrated Polymers

The investigators aim to tackle the difficult challenge of separating ions (charged atoms or molecules) by type from a solution of mixed ion types that have the same charge, similar size and similar chemistry. The investigators propose to use a property called polarizability to achieve this challenging separation. Polarizability is the capacity for electrons to move and shift around a molecule.

These electrons are negatively charged, causing areas of a molecule with a greater number of electrons to be more negatively charged, leaving areas of the molecule with fewer electrons positively charged. This capacity for shifting charges around a molecule, or polarizability, is a key property that influences how ions interact with other molecules.

By changing the number and type of polarizable molecules within the separation membrane, the investigators will learn what fundamental effects this property has on separating ions from a mixture. The ability to design membranes with precise separation performance, especially for these challenging separations of similar ions, will contribute to improving waste-water treatment, reducing environmental contamination, and recycling and recovery processes in the nuclear power industry.

The investigators plan to share their research results through an interactive module, offered during the Open House event, which will introduce a wide audience to issues related to food, water, and energy resource needs.

This proposal aims to investigate ion sorption driven by polarizable functional groups in a polymer membrane. The investigators hypothesize that increasing the polarizability of the functional groups on the polymer backbone will favor sorption of less polarizable ions. To test this hypothesis the investigators will synthesize two series polysulfone-based membranes, one with a fixed number of increasingly polarizable functional groups and the other with varying hydrogen bond-donating functional groups.

The investigators will also test the hypothesis that the polarizability of a hydrated polymer can be increased by clustering functional groups closer together on the polymer backbone, by comparing the side-chain functionalized polymers with block copolymers, where only one block contains the polarizable functionality. The block copolymer architecture allows the polarizable functionality to be localized into segregated regions of the material.

The degree of polarizable functionalization will be confirmed via nuclear magnetic resonance spectroscopy and titration. The resulting membranes will be characterized for the dielectric permittivity, which measures the dielectric constant, and their ion sorption and selectivity properties. The outcome of the proposed activities will be a fundamental understanding of thermodynamically-driven separation processes, which are less thoroughly investigated when compared to size- or diffusivity-driven processes.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.