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

先进的化学传感器使诸如护理点医疗测试和个人防护设备等技术能够抵御化学战剂。化学传感器的日益复杂源于用作传感器的材料的进步或对具有不寻常性质的现有材料的研究。其中一种材料是商用聚合物Nafion，它被用于电解、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，它由氟和碳原子的长疏水（拒水）主链和亲水（亲水）分支组成。这些双重功能产生了高化学稳定性、高反应性和在水存在下的柔韧性。这种双重功能也导致了分子通过材料的独特运输，特别是当制造成薄膜时。现有的理论很好地描述了Nafion膜内小分子的运输。然而，在现有的理论框架内无法解释较大的有机化合物的运输，例如在化学战剂中发现的那些，特别是考虑到Nafion的水引起的灵活性。该项目将使用先进的实验技术来推断通过动态Nafion膜的大型有机分子的运输，这些有机分子是化学战剂的代表。该项目将对有机分子通过Nafion膜的水运输进行直接的机制理解。初步数据表明，在干燥的Nafion中，大的有机分子有效地固定在疏水和亲水结构域之间的三级相间区。这种间期的来源被假设为主链和全氟磺酸侧链之间的氟醚连接。然而，酚类和其他弱有机酸在干燥和潮湿条件下都保持固定化。本项目将探讨界面相，以及块状磺化聚苯乙烯共聚物在混合溶剂体系中大分子有机分子运输中的作用。一个跨学科团队将在高磁场下应用小角度中子散射、x射线散射和核磁共振。如果成功，该研究将解决全氟磺酸和磺化聚苯乙烯膜中明显不同结构域的结构和动态特性之间的关系。具体来说，该研究将确定结构域形态对有机分子的运输、固定化和反应性的影响。该项目将支持研究生教育，创建新的教学模块，并开展社区外展活动，展示聚合膜运输、催化和结构优化的交叉机会。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.