X-ray Diffraction Characterization of the Structure of Zein-Oleic Acid Films

Wide-angle (WAXS) and small-angle X-ray scattering (SAXS) studies of dry granular zein, zein fibers, zein-oleic acid resin, and zein-oleic acid films are reported. WAXS patterns showed two diffuse rings for these samples indicative of noncrystalline structures. Measured d-spacings of ∼ 4.6 Å and ∼ 10.5 Å were found for zein-oleic acid resins and films, consistent with the presence of α-helical segments. The granular zein and zein fibers had ∼ 4.6-Å and ∼ 9.5-Å spacings. Neither the films nor the fibers showed evidence of orientation of the molecular axes. SAXS studies of zein-oleic acid films indicated that the structure of the films was affected by preparation method. Biaxially drawn resin films showed periodicities of ∼ 170 Å along the film surface direction and ∼ 135 Å in the thickness direction, while the cast films had weaker intensity periodicities of ca. 80 Å for all beam directions; a weak, diffuse 45-Å spacing was also observed for both samples. The 170-Å periodicity was present in the resin before deformation and following uniaxial deformation. No SAXS periodicity was observed for the granular zein or zein fibers. Several structural models are presented for the resin films that are consistent with reports in the literature that zein, in solution, consist of prism-like particles consisting of four or more molecules.