Controlling fiber/matrix adhesion with binary self-assembled monolayers
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A mixed self-assembling monolayer was applied to a sapphire fiber using two carbon based molecules, Dodeciltrichlorosilane (DTS), and Bromoundecyltrichlorosilane, (BrUTS), in varying ratios. Fibers were cured in an epoxy matrix and pulled in tension to initiate interfacial cracking. The interfacial toughness was calculated from the data and compared across BrUTS to DTS ratios of 25%, 50%, 75% and 100% as well as unaltered sapphire. After an initial drop in the interfacial toughness from the bare sapphire to the 25% BrUTS to DTS ratio the remaining behavior was linear in the ratio of BrUTS. In addition, a finite element model was created to calculate a mode-mix angle of 53 degrees that was used to successfully compare previous data. The experiments demonstrated an ability to directly control the mechanical properties of the composite by modifying the interfacial region of the fiber and matrix. An interesting byproduct of the work was that the frictional behavior of the fiber/epoxy interface was also affected by the amount of BrUTS on the fiber surface.