The goal of this project is to understand molecular diffusion in two types of complex media - microemulsions and polymer gels. Microemulsions are solutions of aggregated surfactants in water, and they are used in pharmaceutical drug delivery to increase solubility, reduce toxicity, and control the rate of drug release. Polymer gels are water-filled networks of thread-like molecules, and they are used in gel chromatography and membrane filtration to separate molecules. Fibrous gels shrink or swell in response to changes in the liquid between the fibers, which strongly affects their function in ways that are not understood. The investigators will use an optical technique to measure rates of molecular movement in microemulsions and polymer gels. Data will be compared with theory to improve theoretical models for these complex systems.
The diffusion of a hydrophobic solute in the presence of micelles or surfactant aggregates will be measured. In such systems, localized interactions in the interior of the aggregates strongly affect diffusion rates of the solute and the surfactant. Strong solute-matrix interactions also occur in polymer gels, in which polymer fibers hinder solute motion, and solute molecules may induce gel swelling or shrinkage. Diffusion rates in microemulsions and shrinking and swelling in polymer hydrogels will be measured by holographic interferometry, an optical method for monitoring changes in concentration in transparent solutions and gels. Taylor diffusiometry, solid phase microextraction, single-photon counting fluorescence spectroscopy, and osmometry will also be used to measure physical properties needed to compare data to theoretical descriptions of these processes.
