Stretched PEO-LiCF3SO3 films: Polarized IR spectroscopy and X-ray diffraction

The effect of tensile stretching on pure PEO and P(EO)_xLiCF₃SO₃ (x = 10 and 20) films was studied using polarized FTIR spectroscopy, wide angle scattering X-ray scattering (WAXS) and small angle X-ray scattering (SAXS). The polarization effects observed in the spectra are readily explained by the selection rules governing IR transitions and symmetry-based vibrational mode assignments of PEO and the 3:1 compound, P(EO)₃LiTf. The degree of polymer chain orientation in the stretched samples as measured by the average of the second Legendre polynomial was calculated from the dichroic ratio for the PEO helices in both pure PEO and the 20:1 film. The degree of chain orientation was markedly higher in the 20:1 film than in the pure PEO film; however it was difficult to calculate the degree of orientation in the 10:1 film.The addition of LiTf causes a slight increase in the fractional crystallinity of the samples as determined from the WAXS data. Orientation of the films did not significantly affect the fractional crystallinity for the 10:1 and 20:1 samples, whereas a slight decrease in the fractional crystallinity was noted for pure PEO upon stretching. The SAXS data suggested that the average crystal size becomes smaller with the addition of lithium triflate to PEO. The SAXS data also indicated that substantial morphological changes occur upon stretching, since the Bragg peak due to the crystalline-amorphous phase separation disappeared upon stretching. These data, taken together, suggest that in the 10:1 film, the tensile stress tends to form small, unoriented domains of the 3:1 compound.