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

Clemson University, Clemson SC

Investigators

Abstract

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.