The objective of this research is to develop and apply both intrinsic and extrinsic fluorophoric sensors embedded in polymers and composites for monitoring such processes as cure, water uptake, and oxidation via fiber-optic fluorimeter or phosphorimeter. These sensors are molecularly designed to respond to the chemical changes occurring in polymers/composites rather than to the viscosity changes, thus making them potentially more sensitive and quantitatively correlatable to the chemical processes. Sensor molecules are designed to generate fluorescence response at different spectral regions so that each process can be monitored independently, as much as possible. Cure sensors are aromatic diamines either mimicking the cure agent (extrinsic) or the cure agent itself (intrinsic). Uv absorption, excitation and phosphorescence spectra of these cure sensors will be studied in epoxy and polyimide in order to correlate with the extent of cure, and to obtain information on the kinetics and the mechanisms, particularly during chemical imidization. Water uptake will be investigated using as extrinsic sensor, 9-anthroic acid while oxidation will be studied via intrinsic fluorescence. These sensors will be implemented by fiber-optic instrumentation to carry out in-situ monitoring of neat epoxy and polyimide, followed by composites. In composites, surface, bulk, and fiber interphase will be probed for cure extent, cure kinetics, moisture uptake, and oxidation by placement of fiber probe at selective locations. The significance of this project is two-fold; the application of uv-vis/fluorescence as a powerful characterization tool for chemical processes, and the development of "smart" materials with built-in sensors for in-situ optimization of fabrication process as well as monitoring long-term stability of chemical/structural changes.
