Depth-Resolved Structure Analysis of Cylindrical Microdomain in Block Copolymer Thin Film by Grazing-Incidence Small-Angle X‑ray Scattering Utilizing Low-Energy X‑rays

Depth-resolved structure analysis of a polystyrene-<i>b</i>-poly­(2-vinylpyridine) (S2VP) thin film (420 nm thick) was achieved by grazing-incidence small-angle X-ray scattering (GISAXS) utilizing low-energy X-rays (“tender” X-rays). In contrast to techniques utilizing hard X-rays, a gradual change of the penetration depth of soft X-rays around the critical angle of total reflection of a polymer surface is anticipated. In this research, X-ray energy of 2.4 keV was chosen to control the penetration depth and achieve depth-sensitive GISAXS measurement. Microphase-separated structure of the annealed S2VP in the thin film was confirmed to be hexagonally packed cylinders (HEX) aligned parallel to the substrate surface. Significant elongation of the Bragg spots in the <i>q</i>_<i>z</i> direction was observed for an incidence angle close to the critical angle. The experimental full width at half-maximum (fwhm) values of the (11) HEX diffraction spot was interpreted using the theoretical fwhm values estimated using the Laue function considering an attenuation decay of X-ray intensity. The penetration depth was controlled by changing the incident angle, and depth-resolved structure analysis revealed that the hexagonal lattice deformed along the depth direction with the deformation gradually relaxed toward the surface. The observed relaxation behavior is related to the higher mobility of polymer chains near the surface

Clarification of Cross-Linkage Structure in Boric Acid Doped Poly(vinyl alcohol) and Its Model Compound As Studied by an Organized Combination of X‑ray Single-Crystal Structure Analysis, Raman Spectroscopy, and Density Functional Theoretical Calculation

When boric acid (BA) is added to poly­(vinyl alcohol) (PVA), a chemical reaction occurs to form the cross-linkages between the amorphous PVA chains. The local structural change caused by this reaction has been clarified concretely from the microscopic level on the basis of the X-ray-analyzed crystal structure, Raman spectra, and <i>ab initio</i> density functional theory using a model compound produced by the reaction between pentanediol (PENT) and boric acid (PENT–BA). The PENT–BA compound was found to take the TT and TG conformations in the methylene segmental parts depending on the stereoregularity of the PENT molecule itself, <i>meso</i> and <i>racemo</i> configurations, respectively. These two conformations give the Raman bands at the different positions. By comparison of the Raman spectra between the PVA–BA and PENT–BA model compounds, the local structures of PVA chains connected to BA molecules have been derived concretely: the syndiotactic PVA parts in the amorphous region form the TG-type ring structure with the 3-coordinate boron atom, where T and G are trans and gauche conformers, respectively. On the other hand, the isotactic PVA part takes the TT conformation when it forms a ring with boron atom. The thus-created rings are hydrogen-bonded to form a dimer, which plays a role as cross-linkage between the neighboring PVA chain segments in the amorphous region

Macroscopic Alignment of Cylinders via Directional Coalescence of Spheres along Annealing Solvent Permeation Directions in Block Copolymer Thick Films

We reported the long-range perpendicular and horizontal orientation of polystyrene cylinders in polystyrene-<i>b</i>-poly­(methyl acrylate) (PS-<i>b</i>-PMA) films with thickness scale from hundreds micrometers to millimeters. Dissolving block copolymer (BCP) in selective solvents forms PS micelles in solution, which could be trapped in films after ordinary solvent casting. Controllable alignment of perpendicular and horizontal cylinders from the directional coalescences of PS spheres along permeation directions of annealing solvent into the film was achieved, i.e., solvent permeating from surface of film led to perpendicular PS cylinders while from edge resulted in horizontal cylinders. Polarizing optical micrographs and μ-beam SAXS confirmed the directional coalescences mechanism during the orientation process and that the cylindrical structure was achieved throughout a macroscopic scale. Solvent components influenced the orientation behavior, and the mixed solvents containing 25–40% (volume fraction) methanol were favorable to form highly oriented cylinders