Figure 2. (a) Tpp and Tss from IR-DCP and FTIR polarimetry at 0° (top) and 90° (bottom) azimuthal sample rotation. (b) Corresponding polarized phase-difference spectra from IR-DCP and FTIR polarimetry.
The band amplitudes in the IR-DCP transmission and phase spectra at 0° azimuthal angle are slightly larger compared to FTIR. Such differences could be related to the inhomogeneity of the fiber scaffold and the different sizes and opening angles of the probe beam in DCP and FTIR. However, band positions and shapes agree well for both methods. Indeed, the relative phase spectra exhibit the expected Kramers–Kronig consistent line shape, thus demonstrating the validity of the method.
The recorded IR-DCP and FTIR polarimetric phases show a constant offset of approximately 13˚. Its likely origin is the adjustment of incident power via P1 between the Δpp and Δssmeasurements necessitated by a change in the input polarization. For future measurements, an invariant P1 is recommended, for example, by setting P1 to 45˚ and controlling the power through neutral density filters.
Figure 3 (a) shows images of ss- and sp-polarized transmission and absolute phase spectra versus sample azimuth in 10° steps. Maximum band intensities in the Tss images are observed around 90° azimuth, whereas vanishing band intensities in Tsp are seen at 0° and 90° azimuth. The average orientation of transition dipole moments of the related C–O–C vibrational band is therefore aligned predominantly in the direction of the fibers, in agreement with the overall predominant alignment of the fibers in the scaffold.