Light scattering characterization of carbon nanotube dispersions and reinforcement of polymer composites

Dispersion and morphology of carbon nanotubes as well as enhancement for rubber reinforcement are studied. Several approaches including surfactant aids, functionalization and plasma treatment are used to assist dispersion. Several characterization methods are used to assess both the degree of dispersion and the level of reinforcement. Small angle light scattering is carried out as a primary tool to assess structure and dispersion of nanotubes treated through these approaches Stress-strain measurement and dynamic mechanical analysis are performed on elastomeric composites to study polymer reinforcement. These results are divided into five sections.;The first section focuses on dispersion of untreated and acid-treated multi-walled carbon nanofibers (MWNF) suspended in water. Light scattering data provide the first insights into the mechanism by which surface treatment promotes dispersion. Both acid-treated and untreated nanofibers exhibit hierarchical morphology consisting of small-scale aggregates (bundles) that agglomerate to form fractal clusters that eventually precipitate. Although the morphology of the aggregates and agglomerates is nearly independent of surface treatment, their time evolution is quite different. Acid oxidation has little effect on bundle morphology. Rather acid treatment inhibits agglomeration of the bundles.;The second section focuses on dispersion of the solubilized nanofibers. Light scattering data indicate that PEG-functionalized sample is dispersed at small rod-like bundle (side-by-side aggregate) level. Solubilization is achieved not by disrupting small-scale size-by-side bundles, but mainly by completely inhibiting large-scale agglomeration.;The third section focuses on dispersion of plasma-treated carbon nanofibers. Comparison of untreated and plasma-treated nanofibers indicates that plasma treatment facilitates dispersion of nanofibers.;The fourth section focuses on dispersion and structure of single-walled carbon nanotubes (SWNTs) and multi-walled nanofibers (MWNFs) suspended with surfactants. Disordered fractal network of "ropes" is observed for SWNTs whereas the MWNFs show rod-like character on large length scales. Sonication can produce either better dispersion or aggregation depending on the surfactants.;The fifth section focuses on rubber reinforcement by MWNFs. The nanofiber-polyurethane composites show large Payne and Mullins effects. By adding various concentrations of nanofibers, both Young's modulus and the load at high strain increased. A carbon-black filled analogue shows much less enhancement.