Chemical Engineering Department PhD Defense

THE ENGINEERING OF OPTICAL DEVICES FROM INORGANIC-ORGANIC NANOCOMPOSITES

Theodore L. Druffel

April 1, 2009   9:00 a.m.
Ernst Hall Room 212

The assembly of extremely thin films of discrete refractive index and thickness find numerous applications in optical devices such as anti-reflective and mirror coatings. The history of these devices date to the early 20th century and the current state of the art includes vapor phase and sol-gel deposition of metal oxide thin films. The brittle ceramic films often fail in systems undergoing moderate strains. These coatings on plastic substrates are especially troublesome because of the strain mismatch and also due to the high processing temperatures. This dissertation presents a new approach to the deposition of thin film filters using inorganic-organic nanocomposites.

The refractive index of the nanocomposite is manipulated by the volume of nanoparticles and these films can carry nearly 73 percent inorganic particles. Assembled nanocomposite thin film filters are shown in applications ranging from the ultra violet through the visible spectrum and into the infrared. These stacks range from assemblies of a few well engineered layers to nearly 40 discrete layers. Analysis of the thin film filters using spectroscopy and electron microscopes confirms that the nanocomposites behave as designed. Functionalization of the nanoparticles produces a homogeneous dispersion of the inorganic crystals within the film enhancing the optical and mechanical robustness. The elasticity of the nanocomposite is demonstrated by applying large strains never before possible for these optical devices.

The distinct refractive index boundary of the inorganic nanoparticles in the organic polymer can result in haze. The nanocomposites do perform as designed when assembled into thin film optical filters since the path lengths are short so scattering is minimized. Bulk materials will have path lengths several orders of magnitude longer and the particle size becomes a barrier to an optical article with low haze. The models suggest that true nanoparticle dispersions should result in low haze; however, these dispersions are difficult to attain.  The knowledge gained through the research of thin film nanocomposites can be scaled to thicker sections.

About the candidate: Mr. Thad Druffel is a Ph.D candidate in the chemical engineering department at University of Louisville. He is currently working as the Vice President of Applied Research and Development at Optical Dynamics, and leads a group of researchers in the area of optical nanocomposite thin films. He was the architect of the nanoCLEAR product, an antireflective coating for eyeglass lenses, which received a Nano50 award from Nanotech Briefs in 2006. His current research is in the area of utilizing nanocomposites on flexible substrates for photonic applications and has several publications and patent applications related to this research. Mr. Druffel has a unique background that includes research and development topics in the areas of both Mechanical and Chemical Engineering and has been involved in projects ranging from solar and water facilities in Africa to corporate research and development of cutting edge technologies.