Surface energy mapping of Kevlar� fibers by inverse gas chromatography

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The surface energy characteristics of three Kevlar® fibers have been systematically studied using two inverse gas chromatography (IGC) techniques, i.e., at an infinite probe dilution and at a finite probe concentration, with the latter allowing a unique mapping of the surface energy levels, which complements greatly the more traditional characterization of the highest energy sites. The standard thermodynamic parameters, such as the free energy −Δ, and the adsorption enthalpy and entropy (Δ and −Δ), as well as the dispersive and the specific component ( and ΔGsp/Isp) of the fiber surface energy, were determined from the retention behavior at zero coverage of selected molecules of various polarity. The values are between 49–58 mJ m−2 for the three fibers at 50°C. The polar components, ΔGsp or Isp, calculated by three different methods, reveal the polar feature of the fiber surface. It is interesting to note that the adsorption enthalpies Δ for the short chain alkane probes are nearly the same as their liquefaction energies. Using the second IGC approach, i.e., at finite concentration, the isotherms for the adsorption of n-octane and n-hexylamine on the three selected Kevlar® fibers were constructed by the one-peak method. These are shown to be instrumental to establish the corresponding energy distribution functions. The results may indicate that, unlike the alkane probes, the polar molecules interact strongly with the Kevlar® fiber surfaces, which appear, in this case, energetically heterogeneous. The resulting energy distribution mapping opens new avenues towards the surface characterization of the global surface without the restriction of the averaging imposed by other bulk analysis techniques. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 487–500, 1998