Yuji Sasanuma

Characterization of long-periodic layered structures by X-ray diffraction IV: Small angle X-ray diffraction from a superlattice with non-ideal interfaces

Abstract The small angle X-ray diffraction intensity of superlattices (SLs) has been formulated on the basis of a trapeziform composition profile. The analysis using this model enables us to estimate the interface width as well as the layer thicknesses. A GaAs/AlAs SL was characterized according to this method, and the SL period was precisely determined with consideration of the effect of refraction. The scheme presented here has been shown to be useful for studies on structural modifications of SLs with a long period as large as tens of nanometres.

Characterization of long-periodic layered structures by X-ray diffraction III: Structure of a Langmuir-Blodgett film of cadmium arachidate at elevated temperatures

Abstract The thermal behavior of a Langmuir-Blodgett (LB) multilayer of cadmium arachidate (CdA) was investigated by small-angle X-ray diffraction. Before melting, the LB multilayer underwent a three-step structural change: (1) from room temperature to 60°C, rearrangement of the CdA layers; (2) between 60 and 80°C, onset of the pretransitional disordering; (3) above 80°C, conformational change from trans to gauche state in the hydrocarbon chain. The 001 reflection intensity, a measure of the short-range disorder of the multilayer structure, is sensitive to these changes. In contrast, the lattice distortion parameter tends to increase monotonously up to 100°C. This indicates that the long-range order of the multilayer structure is well preserved at temperatures close to the melting point. On cooling down to room temperature after melting, the crystallites of a periodic lamellar structure grow. Their lattice distortion and dimension in the [001] direction are much larger than those of the multilayer before melting.

A point‐focusing small angle x‐ray scattering camera using a doubly curved monochromator of a W/Si multilayer

A point‐focusing small angle x‐ray scattering (SAXS) camera using a doubly curved monochromator of a W/Si multilayer has been designed, constructed, and tested. The two radii of curvature of the monochromator are 20 400 and 7.6 mm. The reflectivity of its first‐order Bragg reflection for CuKα radiation was calculated to be 0.82, being comparable to that (0.81) of its total reflection. By only 10 s x‐ray exposure, scattering from a high‐density polyethylene film was detected on an imaging plate (IP). A rotating‐anode x‐ray generator operated at 40 kV and 30 mA was used. Diffraction from rat‐tail collagen has shown that the optical arrangement gives the Bragg spacing up to, at least, 30 nm for CuKα radiation. Combined with IPs, the camera may permit us to carry out time‐resolved SAXS measurements for phase behaviors of liquid crystals, lipids, polymer alloys, etc., on conventional x‐ray generators available in laboratories.

NATURE OF THE NON-BONDED (C-H)...O INTERACTION OF ETHERS CH3O-(CH2)N-OCH3(N=4-8)

Conformational free energies of dimethoxy ethers CH3O—(CH2)n—OCH3(n= 4–8) were calculated by ab initio molecular orbital calculations at the Hartree–Fock level of theory using the 6-31G* basis set with the electronic correlation effects evaluated using second-order Moller–Plesset theory on the 6-31 + G* basis set. The dimethoxy ethers are model compounds of polyethers [—(CH2)y—O—]x and have been investigated in terms of the non-bonded intramolecular (C—H)⋯O interaction that occurs in the g±g∓ conformations for the C—O/C—C pair. This interaction was found to be attractive (–0.43 kcal mol–1, 1 cal = 4.184 J) only for 1,4-dimethoxybutane (n= 4) and repulsive (0.24–0.77 kcal mol–1) for the other longer ether chains (n 5). The attractive interaction is discussed here in relation to intramolecular (C—H)⋯O hydrogen bonding.

Characterization of long-periodic layered structures by X-ray diffraction II: Lattice distortion of Langmuir-Blodgett films of lead stearate

X-ray 00l reflections from three kinds of 25-layer Langmuir-Blodgett films of lead stearate were measured, using a high resolution reflection Kratky camera system. The accurate thicknesses of a bilayer were evaluated by the modified Bragg law. According to the microstrain, the paracrystalline and the Wilson models, line breadths of the reflections were separated into broadening due to crystallite size and lattice distortion. The crystallite sizes thus obtained agree well with those calculated from the thickness and number of bilayers. Regardless of which distorion model is used, gaussian profiles always give a larger lattice distortion than Cauchy profiles. To describe the lattice distortion of the present specimens, the microstrain and the Wilson models are more favourable than the paracrystalline model. The lattice distortion has been proven to be very sensitive to preparation conditions such as surface pressure and surface treatment of the substrate.

Characterization of long-periodic layered structures by X-ray diffraction I: A system for small angle and intermediate angle X-ray diffraction using a reflection kratky camera

Abstract A high resolution camera has been developed for the small angle X-ray diffraction measurement of long-periodic layered structures such as Langmuir-Blodgett multilayers, superlattices and liquid crystals. A block collimation system known as a Kratky camera is used to produce a very narrow incident beam. The camera is mounted on a computer-controlled goniometer whose sample holder is rotated around a vertical Θ axis by a pulse motor. Measurements can be carried out in a θ-2θ scan, and also in θ or 2θ scans. Processing of the collected data includes smoothing, and correction for absorption, polarization factor and instrumental broadening. The performance of the present system has been demonstrated by observation of diffraction patterns of a Langmuir-Blodgett film of cadmium arachidate and a GaAs/AlAs superlattice.

Structure-property relationships of polyselenoethers [-(CH2)ySe-]x (y=1, 2, and 3) and related polyethers and polysulfides.

Conformational characteristics, solution (melt) properties, and thermal properties of polyselenoethers [-(CH2)ySe-]x ( y=1, 2, and 3) have been revealed by the rotational isomeric state analysis of ab initio molecular orbital calculations and (1)H and (13)C NMR experiments for monomeric model compounds and compared with those of typical polyethers and polysulfides. The comparative results are summarized here as correlations in conformation among model compounds and unperturbed and crystalline states of the polymers, and thermal properties of the polymer crystals are discussed in terms of intramolecular and intermolecular interactions. By ab initio molecular orbital calculations under periodic boundary conditions, helical structures of poly(methylene oxide), poly(methylene sulfide), and poly(methylene selenide), and the crystal structure of poly(ethylene selenide) have been optimized, and their electronic structures have been predicted. A systematic methodology to predict and characterize up to higher-order structures and various physical properties of polymers incorporated in different phases has been attempted to be developed.

Crystalline complex between poly(γ-methyl l-glutamate) and dimethyl phthalate

Abstract The crystalline complex between poly(γ-methyl l -glutamate) (PMLG) and dimethyl phthalate (DMP) has been formed in films cast from a solution in dichloroethane. It has the stoichiometry of 1 mol of DMP to three or four residues of PMLG and shows two definite characteristics in X-ray diffraction patterns; one is the large hexagonal unit cell with the edge of around 28 A and another the ‘extra’ 5.07 A meridional reflection which can not be interpreted by a PMLG α-helical conformation. The structural examination for the films with various DMP contents is carried out by X-ray, viscoelastic, and d.s.c. measurements and the following structure is proposed for the crystalline complex. Four PMLG are associated to form a group which is hexagonally packed and DMP molecules, located in the gaps between groups, form a specific favourable helical structure along PMLG chains in which the van der Waals stacking of benzene rings of DMP is significant.

Characterization of long-periodic layered structures by X-ray diffraction Part VI: Electron density distribution and chain orientation in a Langmuir-Blodgett film of cadmium stearate

Abstract A model for the analysis of X-ray 00/ reflections from Langmuir—Blodgett (LB) films of Y-type structure is presented. In the model, the stoichiometrically minimum neutral unit is considered a structural unit for the X-ray analysis. Our treatment proceeds as follows. The geometrical parameters of the structural unit are optimized by a semiempirical molecular orbital calculation. Next, the direction of the chain orientation with respect to the laboratory frame is determined so as to minimize the discrepancy between the calculated and observed structure factors. The analytical scheme was applied to the diffraction from a LB film of cadmium stearate (CdSt2), and shown to be valid for determination of the longitudinal structure. The stearate chain was revealed to stand normal to the layer surface within several degrees of tilt. Signs of all the structure factors observed from the CdSt2 LB film were shown to be positive, and its electron density distribution was obtained by Fourier synthesis. For Y-type LB films of divalent metallic salts of stearic acid, the effect of the metal atom on the signs of the structure factor is discussed.

Molecular design, synthesis and characterization of aromatic polythioester and polydithioester

Molecular design of poly(ethylene dithioterephthalate) (PETS2) and poly(ethylene tetrathioterephthalate) (PETS4) has been carried out by molecular orbital calculations, NMR experiments, and single crystal X-ray structure analysis for their model compounds and refined rotational isomeric state calculations for the two polymers, and their conformational characteristics, crystal conformations, configurational properties, solubilities, crystallization behaviors, and thermal properties were predicted. For the purpose of the experimental verification, PETS2 and PETS4 were actually prepared and fully characterized. The new polymer, PETS4, was synthesized by an ionic polycondensation reaction using a complex of tetrathioterephthalic acid and piperidinium. The two polymers were characterized by elementary analysis, IR, solubility test, X-ray diffraction, thermal analysis, and solid-state NMR to yield experimental results satisfactorily consistent with the theoretical predictions. Through the actual examples, molecular design of polymers has been proved to be feasible.