Compressed carbon dioxide can be used to solubilize and re-crystallize many solid drug compounds to help with removing impurities and creating solid particles of unique shapes and sizes that can be more bio-available to the body. We study solubilities using a variable volume view-cell with visual access through a sapphire window via the cloud point technique. We also have several high-pressure cells designed with visual access that are used with FTIR and UV-Vis spectroscopy to measure concentrations in supercritical fluids. Thermodynamic models of the solubilities are developed and matched to experimental data. Support has been received from GlaxoSmithKline Pharmaceuticals and Los Alamos National Laboratories for this work.
Most polymers tend to swell and have their glass transition temperature lowered when exposed to compressed carbon dioxide. We take advantage of these facts by exposing commercially important polymers (such as chewing gum base and biodegradable sutures) to carbon dioxide and then diffusing various flavorings and pharmaceutical products into the polymers. We generate longer lasting chewing gum and drug delivery devices using liquid and supercritical carbon dioxide as the environmentally friendly and bio-inert processing fluid. We study the diffusion of materials into and out of the polymers and also the mechanical properties of then polymers once exposed. This work has been supported by GlaxoSmithKline Pharmaceuticals and Wrigley.
Self-Assembled Monolayers and Polymer Films
This project focused on the preparation of alkane, dicarbamate, and partially fluorinated monolayers and polymer films in carbon dioxide and traditional organic solvents. Monolayers of partially fluorinated n-alkanethiols with varying degrees of fluorination were synthesized and characterized so that the influence of the solvent on the monolayer could be understood. To predict monolayer properties as a function of the degree of fluorination, models were created and it was found that many monolayers formed in carbon dioxide had better electrochemical and barrier properties than those formed in traditional liquid solvents. Atom transfer radical polymerization of 2-hydroxyethyl methacrylate from a surface followed by acylation with fluorinated acid chlorides was observed to produce surface-initiated films with fluorocarbon side chains. Notable achievements included the successful preparation of polymer films with extremely low critical surface energies (9 mN/m) and the determination of the fluorocarbon structure within the film. The film resistance (> 100 M•cm2) is the highest ever reported for a surface-initiated polymer film. This work was sponsored by the National Science Foundation.
Material Manipulation at the Nanoscale
We are exploring alternative solvents with significant potential for replacing current aqueous and organic solvents used for nanostructure-dependent applications such as chemical mechanical planarization (CMP) and for the formation of nanoparticles. We are synthesizing metal(0) nanoparticles and nanostructures in carbon dioxide as well as depositing metal particles and films on a variety of surfaces. We are also using liquid and supercritical carbon dioxide for supported catalyst formation. Finally we are trying to disperse, stabilize and react metal and metal oxide particles in supercritical carbon dioxide focusing on iron, copper, and zeolites. Unlike water and many organic solvents, condensed carbon dioxide has an extremely low viscosity and a low surface tension and its properties can easily be tuned while in the supercritical state allowing for unique nanomaterial formation.