Research Initiation Awards: Characterization of Interdiffusion Between Layers of Langmuir-Blodgett Multilayers

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The objective of this program is a quantitative characterization of the degree of interdiffusion between layers of a Langmuir-Blodgett (LB) multilayer as well as an understanding of the interdiffusion mechanism and identification of important parameters. The study will focus on a model system containing two well characterized materials, cadmium arachidate (CdA) and a substituted polyglutamate (PG). The polyglutamate material has a demonstrated low mode loss when used as an optical medium, and the system is chosen to suggest certain characteristics of a potential organic optical device. Interdiffusion between CdA layers separated by a PG bilayer barrier will be followed using neutron reflectometry (NR) complemented with x-ray reflectometry (XR). Interface profiles before and after diffusion will be inferred by reconciling experimental reflectivities with simulated curves calculated using an established matrix formalism. Potential ambiguities in interpretation will be minimized by the combination of two complementary experimental probes, variation of contrast with deuteration, and the use of system components which are well characterized. The expected results will add greatly to the meager existing data on interdiffusion between two-dimensional ordered layers. New insight into the mechanism and controlling parameters of interdiffusion will potentially impact the design of molecular scale organic devices and the study of transport in model biological membranes. Specifically it will be shown if a novel liquid-crystalline-like polymer acts as an effective diffusion barrier.