Date of Award
5-2024
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Chemistry
Committee Chair/Advisor
Dr. Dvora Perahia
Committee Member
Dr. Gary S. Grest
Committee Member
Dr. Rhett C. Smith
Committee Member
Dr. Brian N. Dominy
Committee Member
Dr. Leah B. Casabianca
Abstract
The current study focuses on understanding the effect of clustering on the structure, dynamics, and response of ionomers in melts and solutions using neutron scattering methods combined with atomistic large-scale molecular dynamics (MD) simulations.
Ionizable polymers are used in a wide range of applications, such as in clean energy and biotechnology, where ion transport is integral to the application. Ionizable groups drive cluster formation and often become the dominating force in determining the structure and dynamics of these polymers.
The work consists of five studies. The first study probes the structure of sulfonated polystyrene in toluene solutions tweaked by the addition of ethanol using small-angle neutron scattering (SANS) and MD simulations. We find that a network is formed driven by ionic cluster formation. The addition of ethanol impacts the size of the clusters and their size distribution, which affects the overall structure of these systems.
Following the understanding of the structure of these ionomers in solution, neutron spin echo (NSE) and MD simulations were used to study the dynamics of these systems. From this study, the relationship between polymer dynamics and ionic clusters was established. Two distinctive time scales were needed to describe the motion in these systems, where the slower motion correlated with the effects of the clusters and the faster motion correlated with the non-confined motion of the highly solvated chain segments.
Following the understanding of dynamics of polymers in solutions, the systems were studied under external perturbations, including temperature and solvent dielectrics, using NSE and MD simulations. With increasing the dielectric constant of the solvent, the cluster size decreases, and the dynamics of the system increase. With increasing temperature, the long-lived clusters remain stable, and the polymer remains dynamic.
The next chapter focuses on structure and dynamics of THF swollen melts studied by large scale atomistic MD simulations. THF is as close as possible to a mutual solvent for both the ionic groups and the chains. We measured structure parameters, including the static structure factor, ionic cluster size and distribution, and dynamic parameters, such as mean square displacement and dynamic structure factor. The study finds that THF resides throughout the system and releases constrains of both the chain and ionic groups. While the addition of THF results in larger ionic clusters, all segments become more dynamic.
The last chapter probes the response of THF swollen melts to shear by large scale MD simulations of the same systems whose structure was probed in the previous chapter. Similar to dielectric constant and temperature, shear affects the stability of the ionic clusters. The neutral polymer was compared to the ionic polymer as THF amounts are increased. For all compositions, the shear viscosity decreases with increasing shear rate. However, the decrease depends strongly on the degree of solvation. With increasing solvent, shear affects packing of polymer bundles but only breaks the clusters at a higher shear rate.
Recommended Citation
Kosgallana, Chathurika, "Structure and Dynamics of Complex Fluids Formed by Ionomers: Experimental-Computational Insight" (2024). All Dissertations. 3643.
https://tigerprints.clemson.edu/all_dissertations/3643
Author ORCID Identifier
0000-0002-8511-3092