Characterization of Kevlar fiber surfaces using a newly developed infrared photoacoustic technique

A newly developed infrared photoacoustic technique has been used to obtain information about the orientation of the surface functional groups of Kevlar-49^R fibers. This method involves the use of a highly polarizable gas in the photoacoustic cell and comparison of the spectra with a non-polarizable coupling gas. A highly polarizable inert gas, xenon, enhances the surface modes oriented parallel to the surface and suppresses the intensity of the perpendicular modes. This method shows differences in the structure of the skin and the core of the fibers. The polymer chains in the skin are oriented parallel to the surface, and in the core they are almost radially oriented.