Structure, Properties, And Dynamics Of Nanoparticle-Tethered Polymers
Kim, Sung A
Understanding how polymer [-] nanoparticle interactions influences structure, dynamics, and properties of composites is of fundamental importance for both the science and technology applications of organic [-] inorganic hybrid materials. Great attention has been given to changes organic polymer species undergo in forming polymer nanoparticle composites. This thesis focuses on a specific type of hybrid systems created by densely grafting polymer chains onto inorganic nanoparticles to form self-suspended nanoparticle suspensions in which every polymer chain is both anchored to and confined between the surfaces of neighboring particles. We have studied the hierarchical structure and relaxation dynamics of polymer chains in these self-suspended nanoparticle suspensions. We have investigated the conformations and thermo-physical properties of self-suspended suspensions based on polyethylene glycol (PEG) chains tethered to silica nanoparticles. It is found that the structure and crystallization of confined PEG could be very different depending on the length scale on which the structure is observed. Below the size of one hybrid unit, particle-tethered PEG chains form more stable conformations, whereas tethered PEG is more amorphous than free chains on length scales above one hybrid unit. We also report how tethering, crowding, and confinement by nanoparticles change the viscoelastic and dielectric relaxation dynamics of nanoparticle-tethered polymer chains. In this study, diverse molecular weights of cis-1,4-Polyisoprene (PI), a type A dielectric polymer, is synthesized in the spectrum from unentangled to wellentangled regime with amine end group functionality. By tethering this polymer to nanoparticles at varying grafting densities it is possible to study dynamics of polymer chains under confinement using bulk measurements. Global chain relaxation is conveniently explored since the net dipole moment of an entire chain of cis-1,4-PI is parallel to the end-to-end vector of the tethered molecules. We have found that tethered PI chains exhibit slower relaxation dynamics and are stretched compared to free polymers. We have studied that nanoparticles could impose topological constraints to the tubes of tethered chains when short molecular weight chains are sparsely tethered. In addition, jamming of soft glasses with increasing temperature and decreasing grafting density have been observed from dielectric spectroscopy and rheology experiments.
polymer nanoparticle composites; structure; dynamics
Ph. D., Chemical Engineering
Doctor of Philosophy
dissertation or thesis