Tsutomu Asano

Plastic deformation of oriented lamellae: 1. Cold rolling of β-phase isotactic polypropylene

Abstract Isotactic polypropylene was crystallized by the oriented growth method and the oriented β-phase obtained. This has unidirectional lamellar orientation with the lamellar long axis parallel to the growth direction, the lamellae being twisted along this direction. The sample plates were cold-rolled in three orthogonal directions, and the deformation behaviour of each case was investigated chiefly by wide-angle and small-angle X-ray diffraction methods. It was revealed that deformation takes place by a different mechanism in each case, including rotation of lamellae, interlamellar slip, chain-directional and transversal chain slip. These results are discussed in connection with the anisotropic structure of these samples due to the lamellar orientation. When the β-phase samples are rolled, α-phase crystals appear with c -axis orientation and the proportion increases with draw ratio. For crystallographic reasons it is concluded in this case that by stretching the c -axis orientation is brought about not through block formation of the original β-phase lamellae and incorporation of these blocks into microfibrils, but by melting or unfolding of the original β-phase lamellae and recrystallization to the c -axis-oriented new α-phase.

Phase transitions of phospholipid vesicles under osmotic stress and in the presence of ethylene glycol

The effects of poly(ethylene glycol) (PEG) on the phase transition of phospholipid multilamellar vesicles (MLVs) were investigated by using differential scanning calorimetry (DSC). Main transition temperature (Tm) and the pre-transition temperature (Tp) of neutral phospholipid-, DMPC-1, DPPC- and DSPC-MLVs increased with an increase in PEG concentration. The subtransition temperature of DPPC-MLV also increased with an increase in PEG concentration. These results could be qualitatively explained by enhancement of the lateral packing on the basis of the osmoelastic coupling theory. The pretransition temperature increased faster than the main transition temperature did with an increase in PEG concentration. The increment of Tm depended on the hydrocarbon chain length, the shorter the hydrocarbon chain length was, the larger the increment was. The transition width in the DSC peak was broadened with an increase in PEG concentration. These three above-mentioned effects are the main differences between the effects of the osmotic stress on the phase transition of MLVs and those of hydrostatic pressure. On the other hand, ethylene glycol (EG), which is the monomer of PEG, had a biphasic effect on transition temperature of DPPC-, DSPC-, and DMPC-MLV, reducing Tm and Tp at low concentrations, but increasing Tm and extinguishing pretransition at high concentrations. This is explained by the induction of an interdigitated gel phase at high concentrations of EG, which indicates that EG can easily penetrate into the head group region of the lipid, in contrast with PEG 6K, because EG is small. Temperature-EG concentration phase diagrams for the various PC-MLVs were determined.(ABSTRACT TRUNCATED AT 250 WORDS)

Plastic deformation of oriented lamellae: 3. Drawing behaviour of β-phase isotactic polypropylene

Abstract Specimens consisting of oriented β-phase lamellae of isotactic polypropylene, obtained by crystallization in a temperature gradient, were drawn at various temperatures. The deformation behaviour was investigated by means of stress-strain measurement, X-ray scattering and scanning electron microscopy. Drawings were carried out in two directions, parallel to the lamellar axis (parallel drawing) and perpendicular to it (perpendicular drawing). The maximum apparent stress and Youngs modulus on parallel drawing were always larger than those on perpendicular drawing. Wide-angle X-ray scattering patterns from the specimens drawn at various temperatures showed different deformation behaviours between parallel and perpendicular drawings, which may be explained by the difference of deformation mechanism at the initial stage. As a conclusion, the deformation mechanism is classified into two steps. In the initial stage of deformation, the β-phase material is deformed mainly by interlamellar slippage (the first step). Then, the β-phase crystals are destroyed by Petermann-type unfolding or local melting (the second step). The final c -axis-oriented texture is recrystallized through destruction of the β-phase material.

Structure and mechanical properties of polyethylene-fullerene composites

The microhardness of films of fullerene-polyethylene composites prepared by gelation from semidilute solution, using ultrahigh molecular weight polyethylene (PE) (6×106), has been determined. The composite materials were characterized by optical microscopy and X-ray diffraction techniques. The microhardness of the films is shown to increase notably with the concentration of fullerene particles within the films. In addition, a substantial hardening of the composites is obtained after annealing the materials at high temperatures (Ta=130 °C) and long annealing times (ta=105s). The hardening of the composites with annealing temperature has been identified with the thickening of the PE crystalline lamellae. Comparison of X-ray scattering data and the microhardness values upon annealing leads to the conclusion of phase separation of C60 molecules from the polyethylene crystals within the material. The temperature dependence is discussed in terms of the independent contribution of the PE matrix of the C60 aggregates to the hardness value.

Creep behavior and elastic properties of annealed cold-drawn poly(ethylene terephthalate): The role of the smectic structure as a precursor of crystallization

The creep behavior and elastic properties of cold-drawn poly(ethylene terephthalate) (PET) films, annealed in the range 60–240 °C have been investigated by means of microindentation testing. Two indentation methods have been used. The imaging method has been employed to examine the viscoplastic properties of the polymer materials while the depth-sensing method was used for the determination of Young’s modulus values. The creep behavior (plastic flow) of cold-drawn PET is shown to be intimately correlated to the nanostructural changes occurring upon annealing. The observed decrease in the rate of creep, when the glassy material is annealed at 60 °C, has been associated with the emerging smectic structure, which confers to the material a higher mechanical performance. The elastic properties of the smectic phase are found to be comparable to those of the glassy state. Young’s modulus E values of the semicrystalline samples are discussed in light of the parallel model of crystalline and amorphous layers. E va...

A fitting method for the determination of crystallinity by means of X-ray diffraction

A best-fitting version of the X-ray diffraction method of Gehrke & Zachmann [Makromol. Chem. (1981). 182, 627–635] for crystallinity determination, which is a modification of the method developed by Ruland [Acta Cryst. (1961). 14, 1180–1185], is presented. The data, corrected and normalized to electron units (e.u.), are plotted as I(s)s2 vs s and fitted by pseudo-Voigt functions for the crystalline peaks added to a background scattering IB(s)s2, with IB(s) = (1 − Xc)Iam(s) + Xc〈f(s)2〉[1 − exp(−ks2)], where Iam is the experimental intensity of a completely amorphous sample (also corrected and normalized to e.u.), 〈f(s)2〉 is the mean square atomic scattering factor in the material, Xc is the degree of crystallinity and k is a factor which includes either thermal or lattice disorder, where s = 2(sin θ)/λ. The use of the scattering of the amorphous sample in this non-integral form of the Ruland equations overcomes the problem, encountered with other procedures, of locating the continuous (background) scattering with accuracy. The degree of crystallinity and the disorder factor are supplied directly by the optimization process. Furthermore, the line broadening analysis which allows the determination of crystallite size is automatically obtained as a by product. Samples of polyethylene terephthalate (PET) with different degrees of crystallinity are investigated. The results are compared with those obtained by other methods which do not use fitting techniques.

Interaction of the surface of biomembrane with solvents: structure of multilamellar vesicles of dipalmitoylphosphatidylcholine in acetone-water mixtures

Abstract To investigate the interaction of the surface of biomembranes with solvents systematically, we have studied the structure and phase behavior of multilamellar vesicles of dipalmitoylphosphatidylcholine (DPPC) in acetone-water mixture by X-ray diffraction and differential scanning calorimetry. The solubility of phosphorylcholine and l -α-glycerophosphorylchorine, which are the same molecular structure as the head group of phosphatidylcholine (PC), decreased with an increase in acetone concentration. This result indicates that acetone is a poor solvent for the hydrophilic segments of the surface of the PC membrane, and χ parameter (interaction energy parameter) of the hydrophilic segments of the membrane surface with solvent increases with an increase in acetone concentration. Main transition temperature of DPPC-MLV decreased with an increase in acetone concentration from 0% to 10% (v/v) acetone and increased from 10 to 20% (v/v) acetone concentration. X-Ray diffraction data indicated that DPPC-MLV in Region A (0% to 10% v/v acetone concentrations) was in Lβ′ phase (gel phase with tilted hydrocarbon chains) and that in Region B (10% to 92% (v/v) acetone concentrations) was in LβI phase (gel phase with interdigitated hydrocarbon chains). The biphasic effects of acetone concentration on the main transition temperature can be explained well by the formation of the LβI phase. Lamellar repeat periods of the DPPC-MLV decreased with an increase in acetone concentration in the Region B. At 92% (v/v) acetone, the LβI phase was transformed to Lβ′ phase. From 94% to 96% (v/v), a new X-ray reflection appeared in the intermediate-angle region having a spacing of 0.62 nm and WAXS reflections shifted to higher angle. These results suggests that a hexagonal packing of the head groups on the surface of DPPC bilayer is formed and the entire DPPC molecules are crystallized in the plane of the bilayer. As acetone concentration increased from 97% (v/v), the structure of DPPC-MLV changed gradually into the crystal structure of anhydrous DPPC. Above 99% (v/v) acetone, an X-ray diffraction pattern became almost the same as that of the anhydrous DPPC. These structural changes of DPPC-MLV are discussed by the effect of the χ parameter between the surface of DPPC-MLV and solvents. As acetone concentration increased, χ parameter of the hydrophilic segments of the surface of DPPC membrane with solvents increased, resulting in the decrease of the solvent content inside the DPPC-MLV.

Plastic deformation in polyethylene crystals studied by microindentation hardness

Abstract The microhardness H of films of oriented polyethylene (PE) prepared by gelation from semidilute solution using ultra-high-molecular-weight PE and of films of isotropic melt-crystallized linear PE in a wide range of molecular weights has been determined. Comparison of a thermodynamical approach, which takes into account the dependence of the experimental crystal hardness Hc upon the crystal thickness lc with Youngs dislocation model for yield, gives good agreement for the oriented films. In case of isotropic PE films, only thermodynamic predictions can explain the experimental H c data. The temperature dependence of H c is also discussed in the light of both models. It is found that the softening coefficient of meltcrystallized PE samples depends not only on the thermal lattice expansion but also on the thermal activation of dislocations arising from the finite thickness of the crystals.

Investigation of the melt-crystallization of polypropylene by a temperature slope method

Abstract To investigate the in‐situ ordering process of isotactic polypropylene (iPP) from a melt state, a stationary growth front was prepared by the temperature slope crystallization (TSC) method. During the melt‐crystallization, iPP was crystallized into the α‐phase or β‐phase depending on the crystallizing conditions. The mechanism of the melt‐crystallization at the growth front was precisely observed by wide‐angle and small‐angle x‐ray scattering (WAXS and SAXS) using a strong synchrotron beam. In the TSC apparatus, the sample was crystallized in between a heater, controlled to 220°C, and a cooler, cooled by water to 25°C. We define the z‐axis parallel to the temperature gradient. A‐lamellae and B‐lamellae are also defined as those whose lamellar normal are perpendicular and parallel to the z‐axis, respectively. In a sample‐stop (SS) stage before the TSC, the original α‐phase lamellae became thicker, approaching to the melt‐solid boundary by annealing. The annealing process showed that the α‐phase B‐lamellae remained and the SAXS reflection was stronger on the meridian near the melt‐solid boundary in the SS stage. In the beginning of the TSC, the α‐phase B‐lamellae developed as a primary crystallization. During secondary crystallization under high supercooling, the SAXS cross pattern appeared showing that the α‐phase developed both A‐ and B‐lamellae. As the growth direction of A‐lamellae is parallel to the z‐axis, A‐lamellae grow faster than B‐lamellae. By the self‐epitaxial mechanism on the side surface of the A‐lamellae, the B‐lamellae grow on the base of the A‐lamellae. Following appearance of a spontaneous β‐nucleus, the β‐phase lamellae grew preferentially, excluding the α‐phase, and occupied the whole area of the sample. In this case also, A‐lamellae are advantageous to grow because of the growth direction parallel to the z‐axis. As a result, the SAXS β‐phase reflection appeared on the equator.

Crystallinity of Polymers by X-ray Diffraction: A new fitting Approach

Abstract A new method for determining the crystallinity fraction of semi-crystalline polymers from X-ray powder diffraction measurements is presented. Using the scattering of an amorphous sample of the same material and a convenient expression for the disorder factor, the method can lead to precise separation of the crystalline and amorphous contributions by a fitting procedure. In this way, the crystallinity fraction and the disorder factor are automatically obtained. The method is applied to polyethylene terephthalate.