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

本项目是一个综合性的实验研究项目，基于NMR trans-port成像和创新的机电测试，研究离子聚合物凝胶中的机电耦合。离子聚合物凝胶是一种在极性溶剂中溶胀的具有大量可解离基团的网络。它们表现出一系列不寻常的特性：温度、盐度和pH值的变化会导致自发收缩或膨胀，暴露在电场中会导致变形。相反，压力梯度被转换成可以测量的电场。虽然以前的工作主要集中在离子聚合物凝胶作为致动器的应用，但该项目主要是由它们作为机械传感器的用途所激发的。虽然电场和机械变形之间的耦合在原则上是理解的，但仍存在许多问题。通过求解相应的化学、电学和机械场方程，基于假定的输运机制开发了模型。然而，它们依赖于微观参数，如离子迁移率、扩散系数等，这些参数必须根据观察到的机电响应来估计。为了直接测量这些量，专用NMR探针组件允许在样品暴露于电压和/或压力梯度的同时原位量化离子、溶剂和聚合物的传输。将探讨稳态和瞬态情况。使用NMR成像技术，可以获得空间分辨的信息（与表面相对的内部传输等）。非技术概述：聚合物水凝胶具有令人惊讶的和有用的特性，其中众所周知的是在液体中紧密吸收几倍于其自身重量的能力。同样的材料也可以将机械压力转化为电信号，这使得它们可以用作人工传感器。它们是灵活的和水基的，因此可以安全地植入活体。潜在的应用包括为人造皮肤增加触觉功能，自动药物输送系统以及监测小型化学反应器中的流动。本项目将使用先进的磁共振成像技术来测量水凝胶中盐、水和聚合物的内部传输，以响应压力和电场的变化。研究结果将使我们能够理解这些材料如何将压力转化为电信号，并优化其作为机械传感器的性能。该项目将为几名本科生和研究生提供一个良好的学习环境，使他们接触到与生物学和医学应用密切相关的基础研究问题。

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.