Computational-Experimental Insight across Time and Length Scales of Dynamics in Ionic Polymers

Clemson University, Clemson SC

Investigators

Abstract

NON-TECHNICAL SUMMARY: The design of new materials is one critical aspect of engineering new platforms that will augment the energy security of the nation, impact health, and enhance economic competitiveness. Driving innovation in technologies such as clean energy generation and storage and numerous biomedical technologies requires new materials that can serve in different capacities simultaneously. One promising class of materials consists of very large molecules (polymers) able to transport ions and electrons while retaining their mechanical integrity, often under extreme conditions of high temperatures, solvents, and external stresses that may affect their performance. The ability of these materials to play multiple roles is attained by tailoring molecular segments with different chemical functionalities into one large molecule, including blocks for transporting ions and electrons and blocks to provide mechanical stability. Controlling the way these segments organize and perform electrically as they are integrated into devices is key to the design of new effective platforms. In this project, using large-scale computational studies coupled with state-of-the-art neutron measurements, the effects of the structure of these polymers will be correlated with their dynamics as they are exposed to high temperatures and solvents. The projected results will provide the understanding that will enhance the ability to design well-controlled multi-functional polymers, tailored with desired properties for specific applications. The project is closely integrated with interdisciplinary education and training of graduate and undergraduate students and high-school outreach. TECHNICAL SUMMARY: Polymers that consist of ionizable blocks (ionomers, or polyelectrolytes) tethered to additional segments with well defined functionalities, constitute promising media for a large number of applications from clean energy and storage to sensors and drug delivery vehicles. The role of the ionic groups is two-fold: they form physical crosslinks while facilitating transport of ions and polar guest molecules. As these two functions often require dynamics of opposing nature, the additional blocks affect the overall stability of such polymers. Here, using large-scale molecular dynamics simulations coupled with neutron scattering techniques, the correlation of polymer dynamics with ionic associations and their cohesiveness will be investigated on a series of model copolymers that consist of styrene sulfonate as the ionic block tethered to different non-ionic segments. Numerous studies have probed the structure of ion-containing polymers and polyelectrolytes, revealing a rich variety of morphologies and establishing a clear correlation between structure and transport. One key challenge that arises from these studies is the need to unfold the correlation between ionic associations and their impact on the mobility of the polymers. The relationship of the dynamics with the number, topology, and stability of the ionic associations impacts the polymer properties and in turn affects a large number of technologies. This research is set to resolve the effects of constraints formed by ionic associations on polymer dynamics. Advances in computational techniques coupled with new developments in neutron scattering will enable a new insight into the dynamics of polymers under the confinement of physical crosslinks.