Polymer Additives Effects on Structure and Dynamics

This dissertation presents work that expands the understanding of the effect additives have on the structure and dynamics of a polymer matrix. Polymer additives are molecules, nanoparticles or fibers that are added to a polymer to modify the properties of the host polymer. Due to the vast amount of additives available, our studies were limited to C₆₀ (C60), soft polystyrene nanoparticles, and poly(ethylene oxide).

The first part of this project examined the influence that C₆₀ nanoparticles have on the assembly of polyacrylonitrile using small angle and wide-angle x-ray scattering techniques and viscometry. The addition of C₆₀ (C60) to polyacrylonitrile has little effect to the chain dimensions while in solution but shift the crystalline morphology from hexagonal packing to an orthorhombic space group. Additionally, the C₆₀ (C60) nanoparticle decreases the amount of crystallinity measured in the polymer nanocomposites. This project provides insight into the use of non-covalent interactions between a polymer and nanoparticle to produce a well-dispersed nanocomposite.

The next part of the project focuses on polystyrene center of mass diffusion in the presence of soft polystyrene nanoparticles. The addition of the soft nanoparticles slowed the matrix polymer diffusion when the nanoparticles were larger or the same size as the matrix polymer chains. Although when the nanoparticles were 3 times smaller than the matrix polymer chains the nanoparticles increased the diffusion of the host polymer chains. Additionally, it was shown that the nanoparticles are not stationary, rather that the diffusion of the nanoparticles is best described by the slow mode theory of diffusion.

Finally, poly(ethylene oxide) was studied as an additive to lignin solutions, which mimic the beginning production stages of lignin-based carbon fibers. The study focuses on the influence that poly(ethylene oxide) has on the self-assembly of lignin while in solution. The cylindrical structure of the lignin molecules is isotopically extended along the length of the cylinder with the addition of poly(ethylene oxide) to varying magnitudes depending on the source of the lignin. This work gives insight into the best starting conditions for lignin-based carbon fiber that can maximize the properties of the final product.