3 research outputs found
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>-polyÂ(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><sub><i>z</i></sub> 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 polyÂ(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>-polyÂ(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 ÎĽ-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