Fundamental Mechanisms of Adhesion at the Fiber-Matrix Interface

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The nature of the interface between the fiber and matrix in fiber- reinforced polymers greatly influences overall performance of the composite material. The details of the interactions at this interface are not well understood, however. It is firmly established that modifying the interface can greatly improve performance, the underlying physicochemical mechanisms of adhesion and their relationship to performance have not been established. The three main mechanisms believed to underly the adhesive interaction are mechanical interactions, intermolecular interactions, and chemical binding. Preliminary work by the investigator has shown that a small number of pendant chains covalently attached to a fiber surface significantly increases adhesion between fiber and matrix. An experimental program has been designed to examine the exact cause of the increased adhesion by systematically modifying the surface of Aramid Fibers with pendant groups whose chemical structure provides varying potential for physicochemical interaction with the matrix. A key phase of the research is experimental determination of the exact state of the surface and the pendant groups by means of quantitative dye analysis, nonradiative fluorescence energy transfer, and continuous wetting force measurements. Results will be correlated with adhesion data to delineate the relation between molecular level interfacial details and interfacial adhesive bonding. There is no more important area of research, relative to the future international competitiveness of American industry, than the area of advanced composite materials. The properties of a fiber composite are determined by the matrix, the fiber, and the interface at which they interact. Obtaining understanding and control of this interface is crucial to our ability to engineer composite materials so as to realize their full potential.