Effects of Hydrogen Bond Intermolecular Interactions on the Crystal Spherulite of Poly(3-hydroxybutyrate) and Cellulose Acetate Butyrate Blends: Studied by FT-IR and FT-NIR Imaging Spectroscopy

The crystal melting behaviors of poly­(3-hydroxybutyrate) (PHB) and cellulose acetate butyrate (CAB) blends were studied using infrared (IR) and near-infrared (NIR) imaging, which provided information about spherulite growth in dynamic blend systems. By analyzing the changes in the IR and NIR imaging spectra in the regions of the first and second overtones of the CO stretching vibrations of PHB and CAB, the evolution of heterogeneous spherulite during the time-resolved isothermal crystallization process was explored. Time-resolved IR and NIR imaging and polarized microscopic studies detected the PHB domains are able to separate from the PHB/CAB blends early in the process. Principal component analysis (PCA) was used to classify the distribution of the different morphologies of spherulite. The first principal component suggests that the discrimination of the imaging spectra relies largely upon the crystallinity, while the second principal component indicates the variations in the amorphous portion of PHB, the CAB contents, and the intermolecular hydrogen bonding of PHB and CAB. The PC1–PC2 scores of different parts of the spherulite suggest that the areas of low crystallinity in the blend spherulite contain both PHB and CAB

Rydberg and π–π* Transitions in Film Surfaces of Various Kinds of Nylons Studied by Attenuated Total Reflection Far-Ultraviolet Spectroscopy and Quantum Chemical Calculations: Peak Shifts in the Spectra and Their Relation to Nylon Structure and Hydrogen Bondings

Attenuated total reflection far-ultraviolet (ATR-FUV) spectra in the 145–260 nm region were measured for surfaces (thickness 50–200 nm) of various kinds of nylons in cast films to explore their electronic transitions in the FUV region. ATR-FUV spectra show two major bands near 150 and 200 nm in the surface condensed phase of nylons. Transmittance (Tr) spectra were also observed in particular for the analysis of valence excitations. Time-dependent density functional theory (TD-DFT/CAM-B3LYP) calculations were carried out using the model systems to provide the definitive assignments of their absorption spectra and to elucidate their peak shifts in several nylons, in particular, focusing on their crystal alignment structures and intermolecular hydrogen bondings. Two major bands of nylon films near 150 and 200 nm are characterized as σ-Rydberg 3p and π–π* transitions of nylons, respectively. These assignments are also coherent with those of liquid <i>n</i>-alkanes (<i>n</i> = 5–14) and liquid amides observed previously. The Rydberg transitions are delocalized over the hydrocarbon chains, while the π–π* transitions are relatively localized at the amide group. Differences in the peak positions and intensity were found in both ATR- and Tr-FUV spectra for different nylons. A red-shift of the π–π* amide band in the FUV spectra of nylon-6 and nylon-6/6 models in α-form is attributed to the crystal structure pattern and the intermolecular hydrogen bondings, which result in the different delocalization character of the π–π* transitions and transition dipole coupling

Evolution of Intermediate and Highly Ordered Crystalline States under Spatial Confinement in Poly(3-hydroxybutyrate) Ultrathin Films

The crystallization behavior and crystalline structures of poly­(3-hydroxy­butyrate) (PHB) ultrathin films (∼52 nm) under spatial confinement were investigated using infrared reflection–absorption spectroscopy (IR-RAS) and two-dimensional grazing incidence X-ray diffraction (2D-GIXD). Intermediate and highly ordered crystalline states were observed during heating and melt-cooling of these films. In the ultrathin films, the intermediate state was noticeably stable at lower temperatures, whereas the highly ordered state was more stable at higher temperatures. A transformation from the intermediate state into the highly ordered state occurred as the temperature increased, as the crystals in the intermediate state acquire sufficient thermal energy to overcome the energy barrier. 2D-GIXD results show that the intermediate state was dominant in edge-on lamellae configuration where the crystallographic <i>b</i>-axis is normal to the film surface. Meanwhile, the highly ordered state was predominant in flat-on lamellae configuration where the <i>b</i>-axis is parallel to the film surface. In the surface region, crystals strongly tended to align in an edge-on lamellae configuration

Controlled Terahertz Birefringence in Stretched Poly(lactic acid) Films Investigated by Terahertz Time-Domain Spectroscopy and Wide-Angle X‑ray Scattering

We report a correlation between the dielectric property and structure of stretched poly­(lactic acid) (PLA) films, revealed by polarization-sensitive terahertz time-domain spectroscopy and two-dimensional (2D) wide-angle X-ray scattering (WAXS). The experiments evidence that the dielectric function of the PLA film becomes more anisotropic with increasing draw ratio (DR). This behavior is explained by a classical Lorentz oscillator model assuming polarization-dependent absorption. The birefringence can be systematically altered from 0 to 0.13 by controlling DR. The combination of terahertz spectroscopy and 2D WAXS measurement reveals a clear correlation between the birefringence in the terahertz frequency domain and the degree of orientation of the PLA molecular chains. These findings imply that the birefringence is a result of the orientation of the PLA chains with anisotropic macromolecular vibration modes. Because of a good controllability of the birefringence, polymer-based materials will provide an attractive materials system for phase retarders in the terahertz frequency range

Multistep Crystallization Process Involving Sequential Formations of Density Fluctuations, “Intermediate Structures”, and Lamellar Crystallites: Poly(3-hydroxybutyrate) As Investigated by Time-Resolved Synchrotron SAXS and WAXD

We explored the isothermal crystallization process of poly­(3-hydroxybutyrate) by means of simultaneous measurements of time-resolved wide-angle X-ray diffraction (tr-WAXD) and small-angle X-ray scattering (tr-SAXS) methods. The tr-WAXD analyses involve not only (1) a precise analysis of the integral widths but also the analyses such as (2) two-dimensional correlation spectroscopy (2D-COS) and (3) multivariate curve resolution–alternating least squares (MCR-ALS). The tr-SAXS analyses involve not only (4) the conventional one-dimensional correlation function analysis but also the analyses such as (5) 2D-COS between tr-SAXS and tr-WAXD profiles and (6) 2D-COS of tr-SAXS profiles themselves. These analyses elucidated a multistep crystallization process as classified by region I to III in order of the increasing time. In region I, the density fluctuations are first built up in the amorphous matrix, and then the density-rich regions locally develop “intermediate structures” having the mesomorphic orders between pure amorphous melts and pure crystals [lamellar crystallites (LC)], which then grow into layers of the intermediate structures [defined as mesomorphic layers (ML)] with the long spacings. These results were elucidated by analysis (5) and (6). In region II, LC start to be created from ML, which was elucidated by analysis (1) to (4), and both of the weight fractions of ML (<i>X</i>_inter) and LC (<i>X</i>_crys) increase with time [analysis (3)]. In region III, <i>X</i>_inter and <i>X</i>_crys decreases and increases with time, respectively [analysis (3)], because the transformation form ML to LC dominates the transformation from the density fluctuations to ML. The WAXD profiles due to ML in region I was identified by analysis (1), while those in regions II and III were identified by analysis (3)