ABSTRACT:Grazing incidence X-ray diffraction (GIXD) was performed on three polyurethane films, prepared with polyol OH number of 120, 375, and 600 cast on various substrates, such as silicon, gold, glass, sodium chloride, and zinc phosphated steel. Surface topography did not affect the structural variation of polyurethane films along with the film depth controlled by an angle of incidence. Change of the crystallinity was occurred by a simultaneous change of interplanar spacing, indicating that substrate-induced crystallization took place. The depth that the substrate surface influenced the crystallization of the polyurethane films corresponded to the halfway of the variation of interplanar spacing. The substrate-induced ordering of the polyurethane films varied according to the substrate surface conditions, presumably depending on the attraction force forward the heterogeneities inside the polymer bulk film. It was suggested that the substrate-induced crystallization of the polyurethane on the various substrates depends on the mobility of heterogeneities toward the polar substrate surface rather than other possible mechanisms such as temperature gradient, chemical similarity, lattice match, and thermal shear stress.KEY WORDS Substrate-Induced Ordering / Polyurethane Thin Film / Grazing Incidence X-ray Diffraction / When a polymer is used as a facing film on substrate, the mobility of polymer chains is restricted by the presence of the substrate surface. The substrate surface provides the sites where polymer molecules reside. In the case where the polymer chains arrange in a periodic registry, the nucleation and growth of the polymer crystalline phase take place at the substrate surface. It is because the surface has a nucleating efficiency equal to or greater than that of the other nuclei within the polymer film, 1 the nucleation is heavily favored at the substrate surface, followed by the formation of substrate-induced crystalline region (SICR).It has been emphasized that the lattice matching is the most important factor for the SICR formation, 2-5 since the nucleating efficiency increases with closeness of match between the lattice parameters of the substrate and the forming polymer crystal. However, the SICR appears even in little similarity in unit cell parameters, 6,7 implying that lattice match between the crystallizing polymer and the substrate material is not a necessary condition for the formation of the SICR. Although temperature gradient between the substrate surface and polymer film influences the nucleation and growth process of the SICR, this does not also appear to be necessary for the SICR to form; isothermally crystallized polypropylene has been observed on nylon fiber substrate which has improbable temperature gradient. 6 Surface energy of the substrate material has been considered as a formation mechanism of the SICR, but both low energy surface (i.e., Terylene) and high energy surface (i.e., graphite) revealed the SICR morphology. [7][8][9][10][11][12] Surface topography partially explains th...
