Collaborative Research: The Role of Sulfonated Polymer Membrane Morphology in Microscale Transport of Organic Molecules

先进的化学传感器使医疗现场医疗测试和针对化学战剂的个人防护设备等技术成为可能。化学传感器的日益复杂源于用作传感器的材料的进步，或者是在研究具有不寻常性质的现有材料方面。其中一种材料是商用聚合物Nafion，它用于电解、矿物提取、特种化学合成、电化学传感器和燃料电池。Nafion的广泛使用是由于其独特的化学结构，它由长的疏水(憎水)氟和碳原子主干和亲水(亲水)分支组成。这些双重功能带来了高化学稳定性、高反应性和在水存在下的灵活性。这种双重功能还导致了分子在材料中的独特传输，特别是在制造成薄膜时。现有的理论很好地描述了小分子在Nafion膜内的传输。然而，较大的有机化合物的运输，如那些在化学战剂中发现的，不能在现有的理论框架内解释，特别是当考虑到Nafion的水诱导灵活性时。该项目将使用先进的实验技术来推断代表化学战剂的大有机分子通过动态Nafion膜的传输。该项目将直接从机理上理解水使有机分子通过Nafion膜的传输。初步数据表明，在干燥的Nafion中，大的有机分子被有效地固定在疏水和亲水区域之间的第三界面区。这种界面相的来源被假设为主链和全氟磺酸侧链之间的氟醚键。然而，酚和其他弱有机酸在干燥和潮湿条件下都保持固定。这个项目将探索界面，以及本体磺化聚苯乙烯共聚物在混合溶剂体系中传输大分子有机分子的作用。一个跨学科的团队将在高磁场下使用小角中子散射、X射线散射和核磁共振。如果成功，这项拟议的研究将解决全氟磺酸和磺化聚苯乙烯膜中截然不同的结构和动态性质之间的关系。具体地说，这项研究将确定结构域形态对有机分子的运输、固定化和反应活性的影响。该项目将支持研究生教育，创建新的教学模块，并开展社区推广活动，展示聚合膜在运输、催化和结构优化方面的机会。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Advanced chemical sensors enable technologies such as point-of-care medical testing and personal protective equipment against chemical warfare agents. Increasing sophistication of the chemical sensors derives from advances in the materials used as the sensor or in studying existing materials with unusual properties. One such material is the commercial polymer, Nafion, which is used in electrolysis, mineral extraction, specialty chemical synthesis, electrochemical sensors, and fuel cells. The widespread use of Nafion is due to its unique chemical structure, which is comprised of a long hydrophobic (water repellent) backbone of fluorine and carbon atoms and hydrophilic (water loving) branches. These dual functionalities give rise to high chemical stability, high reactivity, and flexibility in the presence of water. The dual functionality also leads to unique transport of molecules through the material, particularly when fabricated into a thin membrane. Transport of small molecules within the Nafion membrane is well described by existing theories. However, transport of larger organic compounds, such as those found in chemical warfare agents, cannot be explained within existing theoretical frameworks, particularly when the water-induced flexibility of Nafion is considered. This project will use advanced experimental techniques to deduce transport of large organic molecules that are representative of chemical warfare agents through the dynamic Nafion membrane. This project will develop a direct mechanistic understanding of water-enabled transport of organic molecules through Nafion membranes. Preliminary data suggests large organic molecules are effectively immobilized in a tertiary interphase region between hydrophobic and hydrophilic domains in dry Nafion. The source of this interphase is hypothesized to be the fluoroether linkage between the backbone and the perfluorosulfonic acid side chains. However, phenols and other weak organic acids remain immobilized under both dry and wet conditions. This project will probe the interphase, and the role of bulk sulfonated polystyrene copolymers on transport of large organic molecules in mixed solvent systems. An interdisciplinary team will employ small angle neutron scattering, X-ray scattering, and nuclear magnetic resonance at high magnetic fields. If successful, the proposed research will resolve the relationship between the structural and dynamic properties of the distinctly different domains in perfluorosulfonic acid and sulfonated polystyrene membranes. Specifically, the investigation will determine impact of domain morphology on the transport, immobilization, and reactivity of organic molecules. The project will support graduate education, create new teaching modules, and community outreach activities that demonstrate opportunities at the intersection of transport, catalysis and structure optimization of polymeric membranes.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.