NMR Study of Transport Processes in Ionic Polymer Gels for Sensor Applications

University Of Connecticut, Storrs CT

Investigators

Abstract

TECHNICAL SUMMARY: This project is a comprehensive experimental research program, based on NMR trans-port imaging and innovative electromechanical testing, to study the electromechanical coupling in ionic polymer gels. Ionic polymer gels are networks with a substantial con-centration of dissociable groups, swollen in a polar solvent. They exhibit a range of un-usual properties: changes in temperature, salinity, and pH can lead to spontaneous shrinkage or swelling, and exposure to electric fields causes deformations. Conversely, pressure gradients are translated into electric fields that can be measured. While prior work has mostly focused on the application of ionic polymer gels as actuators, this pro-ject is mainly motivated by their use as mechanical sensors. While the coupling between electric fields and mechanical deformation is understood in principle, many questions remain. Models have been developed based on postulated transport mechanisms by solving the corresponding chemical, electrical, and mechani-cal field equations. However, they rely on microscopic parameters such as ionic mobili-ties, diffusion coefficients, etc, which must be estimated from the observed electrome-chanical response. In order to measure these quantities directly, a dedicated NMR probe assembly that allows to quantify the transport of ions, solvent, and polymer in situ, while the sample is exposed to voltage and/or pressure gradients. Both steady-state and transient situations will be explored. Using NMR imaging techniques, spatially resolved information can be obtained (transport in the interior as opposed to the sur-face, etc). NON-TECHNICAL SUMMARY: Polymer hydrogels have surprising and useful properties, among which the well-known capacity to tightly absorb several times their own weight in liquid. The same materials also translate mechanical pressure into electrical signals, which makes them useful as artificial sensors. They are flexible and water-based, and can therefore be implanted safely into living bodies. Potential applications include adding tactile function to artificial skin, automated drug delivery systems, as well as the monitoring of flow in miniaturized chemical reactors. The present project will use advanced magnetic resonance imaging techniques to measure the internal transport of salt, water, and polymer in hydrogels in response to changes in pressure and electric field. The results will allow us to under-stand how these materials transform pressure into electrical signals, and to optimize their performance as mechanical sensors. The project will provide an excellent learning environment to several undergraduate and graduate students, exposing them to fundamental research questions that are of imme-diate relevance to applications in biology and medicine.