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

非技术摘要：本项目的重点是离子共聚物，这是一种由能够实现离子传输的链段组成的大分子家族，与能够增强机械稳定性的链段相连。这种聚合物材料在创新技术中显示出作为膜的前景，例如，轻型清洁能源的产生和储存、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的过程中形成的结构。这是一个很大的障碍，因为这些结构决定了聚合物薄膜的性能，从而控制了它们在器件中的潜在用途。膜结构受聚合物块之间以及每个块与溶剂之间的相互作用以及工艺条件的影响。控制结构的障碍源于离子段聚集并形成区域的趋势，这些区域在膜形成过程中保持被捕获并锁定聚合物。使用由实验研究支持的计算工具，该项目将确定延长流动和溶剂蒸发时离子共聚物的结构演变。工作假说是，通过流动下的溶剂调整，在不“锁定”其余嵌段的情况下“解锁”离子团簇，将能够形成受控的、定义明确的离子共聚物膜。有了先进的计算工具，再加上结构确定技术，该项目将为聚合物加工提供基本的见解。这些知识将直接推动科学和技术的进步，从而促进国家的经济健康和繁荣。技术摘要：随着在动态条件下理解离子聚合物的巨大挑战，这项研究将努力捕捉溶液中离子嵌段共聚物在伸长流动和溶剂蒸发时结构的时间演变。这项研究将利用选择性中子研究支持的非平衡分子动力学模拟，捕捉聚合物加工的基本原理。这项研究的工作假设是，在不“锁定”疏水区块的情况下，“解锁”离子团簇将能够在离子共聚物膜中形成受控的、定义明确的结构。这一过程可以通过操纵溶剂流动歧管来实现，该歧管将控制离子共聚物的结构，从而控制其性能。一组定义明确的含有聚苯磺酸盐可电离块的二块和三块，在每个块的选择性溶剂和所有块的六元溶剂的溶液中，将在伸长流动中和当溶剂蒸发时进行研究。这项研究将解决在动态条件下导致所有块的“解锁-解锁”状态的参数，以及它对整齐的可电离相整体结构的影响。要了解几个高度不相容的嵌段之间的微妙平衡以及它们在静止条件下和流场下与溶剂的相互作用，面临着实验和计算方面的挑战。然而，随着离子共聚合物溶剂流动响应的结构演变，计算研究和实验工作的融合将提供所需的多时间-长度-尺度的洞察力，这对于推动可电离共聚物的结构至关重要。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。

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.