The properties and performance of carbon fiber reinforced polymer matrix composites are highly influenced by the chemical interactions of the fiber/matrix interface region. Many researchers have hypothesized that the presence of carbon fibers in epoxy causes a chemical gradient to form around the fiber during the curing stage. However, the chemical makeup of the interphase region and how it influences composite behavior is yet to be fully understood. One of the obstacles has been the lack of experimental techniques available to chemically probe the interphase with sufficient resolution.
High-resolution spectroscopy techniques recently developed to study biological processes at the cellular level also have significant potential for characterization of synthetic materials systems. Here, we apply atomic force microscopy based infrared (AFM-IR) spectroscopy to investigate the interphase region developed between carbon fibers and epoxy matrix in an aerospace-grade composite material. The working principle of the technique will be reviewed and key findings will be highlighted. AFM-IR spectra of the bulk matrix material are in excellent agreement with spectra collected by traditional FTIR in both the low wavenumber range (900-1700/cm) and in the high wavenumber range (more than 2500/cm). Chemical maps of the interphase region provide preliminary evidence for distinct variations in matrix chemistry near the fiber surface in comparison to bulk.
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