Alignment strategies for fullerenes and their dimers using soft matter

The overall goal of this research was to achieve alignment of endohedral fullerene dimers defined as covalently linked pairs of fullerene cages where each fullerene cage encapsulates a spin-active atom. The first section will discuss polymer-fullerene interactions from the point of view of determining how various polymer functional groups enhance or hinder the miscibility of C60. In order to successfully incorporate fullerenes into a block copolymer system, we first need to understand the basic interactions that occur between polymers and fullerenes to anticipate the upper limit of fullerenes that may be incorporated in a given polymer and potential approaches to increase this quantity. In particular, studies conducted using wide angle x-ray scattering (WAXS) of vinyl polymer-fullerene blends indicated that an increasing number of phenyl rings in the vinyl side group of the polymer leads to an increase in the miscibility. In particular, poly(9-vinylphenanthrene) (P9VPh), having three phenyl rings in the side group, showed a 6-fold improvement in miscibility limit compared to the other systems studied, polystyrene (PS) and poly(2-vinylnaphathalene) (P2VN). The degree of increase in miscibility observed with P9VPh is attributed to the ability of the vinyl aromatic structure to essentially conform to the curvature of a fullerene molecule rather than the increased potential for pi-pi interactions. These results importantly suggest that a block copolymer system can be tuned to maximize fullerene content, particularly by considering the geometry of functional groups with respect to the fullerene cage and will be discussed further in Chapter III.;Second, the use of block copolymers as templates for creating ordered arrays of fullerenes is discussed. The initial goal was to disperse the fullerenes in one block of a block copolymer system and by aligning the microphase separation structure, also align the incorporated fullerenes. There are several major challenges associated with incorporating fullerenes into a block copolymer including the limited miscibility discussed in Chapter III. Furthermore, overcoming the strong inter-fullerene interactions that lead to aggregation also proves to be challenging; aggregates can disrupt the microphase structure in a block copolymer and make alignment difficult to obtain. One potential method generically used to solubilize nanoparticles within a block copolymer is modification of the nanoparticles by grafting polymer chains to the surface to solubilize the nanoparticle in a specific block. As discussed in Chapter IV, the effects of nanoparticle size and concentration on the phase behavior of lamellar-forming dPS-PMMA systems as well as the location of the fullerene star within the dPS block were studied using neutron reflectivity (NR).;The scheme above has the disadvantage that modification of the fullerene cage with polymer arms dilutes the overall quantity of fullerene in the system and in the case of endohedral systems, would dilute and severely limit the overall quantity of spins available for measurement in quantum computing. For this reason we chose to investigate the formation of monolayers of amphiphilic fullerene dimers at the air/water interface using the Langmuir technique. We also studied the behavior of these materials when transferred as monolayers and multilayers to solid substrates as Langmuir-Blodgett (LB) films. The fullerene dimers in this case were modified to have at least one hydrophilic, polyethylene glycol-based ligand to balance the inherently hydrophobic nature of the fullerene cage and allow for a molecule that more closely resembled typical LB materials. Results of these studies indicated that we can form stable, close-packed monolayers and also control the orientation of the dimer at the air/water interface as well as on solid substrates by tuning the ligand chemistry as shown in Chapter V.;The final approach used to achieve alignment of fullerene materials involves the interaction of fullerenes with a chemically-modified substrate either covalently or non-covalently. Solid substrates were functionalized with amine-terminated molecules, and fullerene materials were then studied for their monolayer formation on these substrates. Results indicate that monolayers of fullerenes can be obtained on both silicon and mica using this technique. Monolayers formed between fullerenes (either monomer or dimer) and amine-terminated surfaces are covalently bound, either through reaction with functional groups or direct addition to the fullerene cage. Endohedral systems were also studied using this approach and results are provided in Chapter VI for studies using this method. (Abstract shortened by UMI.)...