A commercial epoxy, diglycidyl ether of bisphenol-A, was modified by two different routes. One was the addition of silica to produce epoxy composites. Three different silane coupling agents, glycidyloxypropyl trimethoxy silane (GPS), -methacryloxypropyl trimethoxy silane (MAMS) and 3-mercaptopropyltriethoxy silane (MPS), were used as silica-surface modifiers. The effects of silica content, together with the effects of chemical surface treatment of silica, were studied. The results indicate that epoxy composites with silica exhibit mechanical and tribological properties as well as curing kinetics different than the pure epoxy. The optimum silica content for improved mechanical and tribological properties (low friction coefficient and wear rate) was different for each type of silane coupling agent. An unequivocal correlation between good mechanical and improved tribological properties was not found. Activation energy of overall reactions was affected by the addition of silica modified with MAMS and MPS, but not with GPS. The second route was modification by fluorination. A new fluoro-epoxy oligomer was synthesized and incorporated into a commercial epoxy by a conventional blending method. The oligomer functioned as a catalyst in the curing of epoxy and polyamine. Thermal stability of the blends decreased slightly at a high oligomer content. Higher wear resistance, lower friction coefficient and higher toughness were found with increasing oligomer content; thus in this case there was a correlation between good mechanical and improved tribological properties. The results indicated that increasing toughness and formation of a transfer film contribute to improved tribological performances.

An adaptation of an extrinsic Fabry-Perot interferometer (EFPI) strain sensor is described, which permits the state of cure of an epoxy matrix to be monitored, when the sensor is embedded in a polymeric matrix composite. By using a glass rod with a retroreflecting end for the target fiber in the EFPI sensor, the intensity of the light reflected depends on the refractive index of the host matrix, if a low coherence source is used. As the epoxy cross-links during cure, the refractive index of the epoxy will increase to a value exceeding that of the target fiber. The resulting increased loss in the fiber can be detected at the sensor output and correlated to the state of cure of the epoxy. After cure, the sensor may be operated as a conventional extrinsic Fabry-Perot interferometric strain sensor if a coherent source is used. Using the modified extrinsic Fabry-Perot sensor, we monitor the cure of Devcon® 5-Minute® Epoxy, and show that it cures in approximately 60 minutes. / Master of Science

The state of cure of epoxies is an important issue in the manufacture of graphite epoxy composites used in aerospace structures. Variations in the initial state and process used to cure the epoxy resin in a composite material lead to variations in the mechanical properties of the part manufactured from the composite._[12] Control of these variation can be accomplished by monitoring the bulk and shear moduli of the epoxy resin as it cures. The moduli properties of the resin determine the acoustic properties of the epoxy._{[12],[13],[14]} Hence measurement of the acoustic longitudinal velocity and attenuation of the epoxy during its cure cycle provides a good indicator of the state of cure. Optical fiber waveguides can be embedded within a host material and used to detect longitudinal acoustic waves._[15],[16] Herein, the mechanisms allowing the detection of ultrasound with optical fiber are presented. An analysis of optical fiber waveguides and optical fiber based interferometric detection methods is performed in detail. The interaction of radial strain fields, induced by longitudinal acoustic waves, with singlemode optical fibers is described. Experimental results obtained in epoxy cure monitoring, using an optical fiber based method for acoustic detection, are compared with results obtained using conventional piezoelectric based acoustic detection methods. / Master of Science