Structure Regulation of Ionic Copolymers: Unlocking Ionic Clusters through Solvent Shear Adaptation, a Computational-Experimental Insight

非技术摘要：该项目重点研究离子共聚物，这是一种大分子家族，由能够实现离子传输的链段组成，并与能够增强机械稳定性的链段相连。这种聚合物材料有望作为膜用于创新技术，例如轻质清洁能源的产生和存储、水净化和生物医学应用。然而，科学家们还无法控制这些聚合物在加工成膜过程中形成的结构。这是一个重大的障碍，因为这些结构决定了聚合物薄膜的性能，从而控制了它们在设备中的潜在用途。 膜结构由聚合物嵌段之间以及每个嵌段与溶剂之间的相互作用以及加工条件决定。控制结构的障碍源于离子链段聚集并形成在膜形成过程中保持捕获并“锁定”聚合物的区域的倾向。 该项目将利用实验研究支持的计算工具，确定离子共聚物在拉伸流动和溶剂蒸发时的结构演变。工作假设是，通过在流动下调节溶剂，“解锁”离子簇而不“锁定”其余嵌段，将能够形成受控的、结构明确的离子共聚物膜。借助先进的计算工具，再加上结构测定技术，该项目将为聚合物加工提供基本见解。这些知识将直接促进科学技术的进步，从而促进国家的经济健康和繁荣。 技术摘要：面对理解动态条件下离子聚合物的巨大挑战，该研究将努力捕捉溶液中离子嵌段共聚物结构在拉伸流动和溶剂蒸发时的时间演化。该研究将利用非平衡分子动力学模拟，在选择性中子研究的支持下，掌握聚合物加工的基本原理。该研究的工作假设是“解锁”离子簇而不“锁定”疏水嵌段将能够在离子共聚物膜中形成受控的明确结构。该过程可以通过操纵溶剂流歧管来实现，该歧管将控制离子共聚物的结构及其性能。 一组明确的二嵌段和三嵌段包含聚苯乙烯磺酸盐可电离嵌段，在每个嵌段的选择性溶剂和所有嵌段的θ溶剂的溶液中，将在拉伸流动和溶剂蒸发中进行研究。该研究将解决在动态条件下导致所有块体处于“解锁-解锁”状态的参数，及其对纯电离相整体结构的影响。了解几种高度不相容的块的微妙平衡及其在静态条件和流场下与溶剂的相互作用提出了实验和计算挑战。然而，离子共聚物溶剂流响应的结构演变后计算研究和实验工作的融合将提供驱动可电离共聚物结构所需的多时间长度尺度的洞察力。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

NON-TECHNICAL SUMMARY:This project focuses on ionic copolymers, a family of macromolecules comprised of segments that enable ionic transport, tethered to ones that can enhance mechanical stability. Such polymer materials show promise as membranes for use in innovative technologies, for example, light-weight clean energy generation and storage, water purification, and biomedical applications. However, scientists cannot yet control the structures these polymers form during their processing into membranes. This presents a significant roadblock since these structures determine the properties of the polymer films, and hence control their potential use for devices. The membrane structure is governed by interactions among the polymer blocks and between each of the blocks with the solvent, as well as processing conditions. The barrier to controlling the structure stems from the tendency of the ionic segments to aggregate and form regions that remain trapped and "lock" the polymers during membrane formation. Using computational tools supported by experimental studies, the project will determine the structure evolution of ionic co-polymers in elongational flow and as the solvents evaporate. The working hypothesis is that "unlocking" the ionic clusters without "locking" the rest of the blocks, through solvent tuning under flow, will enable the formation of controlled, well-defined structured membranes of ionic co-polymers. With advanced computational tools, coupled with structure determination techniques, the project will provide fundamental insights into polymer processing. This knowledge will directly promote the progress of science and technologies that will advance the economic health and prosperity of the nation. TECHNICAL SUMMARY: With the grand challenge of understanding ionic polymers under dynamic conditions, the research will strive to capture the time evolution of the structure of ionic block co-polymers in solutions in elongational flow and as solvents evaporate. The study will capture polymer processing fundamentals, using non-equilibrium molecular dynamics simulations, supported by selective neutron studies. The working hypothesis of the proposed research is that "unlocking" the ionic clusters without "locking" the hydrophobic blocks will enable the formation of controlled well-defined structures in ionic copolymer membranes. This process is achievable by manipulating a solvent-flow manifold that will control the structure of ionic copolymers and consequently their properties. A set of well-defined diblocks and triblocks that contain polystyrene sulfonate ionizable blocks, in solutions of selective solvents for each of the blocks and theta-solvents for all blocks, will be studied in elongational flow and as the solvents evaporate. The study will resolve the parameters that lead to the "unlocked-unlocked" state for all blocks under dynamic conditions, and its effect on the overall structure of the neat ionizable phases. Understanding the delicate balance of several highly incompatible blocks and their interactions with solvents under quiescent conditions and under flow fields presents experimental and computational challenges. However, the convergence of computational studies and experimental efforts following the structure evolution of ionic co-polymers solvent-flow response will provide the required multi-time-length-scale insight essential to drive the structure of ionizable copolymers..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.