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

技术概述：本项目是一个基于核磁共振传输成像和创新机电测试的综合性实验研究项目，旨在研究离子聚合物凝胶中的机电耦合。离子聚合物凝胶是具有大量可解离基团的网络，在极性溶剂中膨胀。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。虽然之前的工作主要集中在离子聚合物凝胶作为致动器的应用上，但本项目主要是将其用作机械传感器。虽然电场和机械变形之间的耦合在原则上是可以理解的，但仍然存在许多问题。通过求解相应的化学、电和力学场方程，建立了基于假设输运机制的模型。然而，它们依赖于微观参数，如离子迁移率、扩散系数等，这些参数必须从观察到的电化学响应中估计出来。为了直接测量这些数量，一个专用的NMR探针组件，允许量化离子，溶剂和聚合物的原位运输，而样品暴露于电压和/或压力梯度。将探讨稳态和瞬态情况。利用核磁共振成像技术，可以获得空间分辨信息（内部传输而不是表面传输等）。非技术概述：聚合物水凝胶具有令人惊讶和有用的特性，其中众所周知的能力是紧紧吸收数倍于自身重量的液体。同样的材料还能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。它们是柔韧的水基材料，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量。目前的项目将使用先进的磁共振成像技术来测量水凝胶中盐、水和聚合物的内部运输，以响应压力和电场的变化。研究结果将使我们了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。该项目将为一些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直接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.