Kazumi Matsushige

The II-I crystal transformation of poly(vinylidene fluoride) under tensile and compressional stresses

Abstract The mechanism for a crystal transformation in poly(vinylidene fluoride) by a tensile deformation at atmospheric pressure was investigated in the temperature range 25–150 °C. Simultaneous X-ray and stress-strain relationship measurements during the drawing process revealed that the crystal transformation from Form II to Form I occurred at the temperatures below 130°C where the sample deformed by cold-drawing, and always initiated at the deformation stage where necking was completed at the centre of the tensile sample. Above 140°C, on the other hand, the sample deformed uniformly without necking and did not perform the crystal transformation. Thus, it was suggested that a heterogeneous stress distribution in the sample played a critically important role in the crystal transformation phenomenon. A uniaxial compressional deformation also caused the crystal transformation from Form II to Form I in this sample. The crystal conversion ratio varied with the conditions of compressional pressure and temperature, and the molecular orientation in resultant samples depended on the shapes of the anvils employed in the compression experiment. By applying a high d.c. voltage during the compressional deformation, a highly uniaxially oriented Form I film with prominent piezoelectric properties was obtained.

Crystallization of macromolecules under high pressure

Abstract The following facts have been clarified by DTA, PSPC X-ray scattering, ultrasonic measurements, optical microscopy, and Raman spectroscopy under high pressure. At high pressure on heating polyethylene has a transition from an extended-chain orthorhombic phase to a liquid crystal-like hexagonal phase after passing through a lamella-thickening of the folded-chain orthorhombic phase and finally melts. On cooling polyethylene has a transition from the liquid crystal-like hexagonal phase to the extended-chain orthorhombic phase after passing through a two-dimensional diffusion controlled crystallization. At high pressure on heating poly(vinylidene fluoride) has a transformation from the folded-chain form II crystal to the folded-chain form I crystal. On further heating folded-chain and extended-chain form I crystals melt after passing through a lamella-thickening stage. On cooling a two-step crystallization of extended-chain and folded-chain form I crystals occurs. Furthermore, the crystal transformation from form II to form I was observed to proceed with an activation energy of 30 kcal/mol on annealing at 4000 kg/cm2. The high-pressure annealing procedure was utilized to improve piezoelectricity of poly(vinylidene fluoride) film. The mechanism of improvement is discussed.

Structural evaluation of epitaxially grown organic evaporated films by total reflection x‐ray diffractometer

An in‐plane‐type total reflection x‐ray diffractometer was newly constructed, and the epitaxial growth of paraffin molecules (n‐C33H68) vacuum‐evaporated onto a KCl (001) surface was investigated. The molecular chains in as‐evaporated films were shown to arrange themselves parallel to the 〈110〉 direction of the KCl substrate. After the evaporation, moreover, some molecules were revealed to reorient and tend to deviate their c axis by about ±5° from the 〈110〉 direction of the KCl crystal, probably because of the lattice mismatchings between the paraffin and substrate crystals.

THE VISCOELASTIC PROPERTIES OF THE HUMAN SEMILUNAR CARTILAGE

Abstract We performed the experiment to observe the mechanical and physical properties of the semilunar cartilage in the knee of the pig and the human, which were preserved in silicone oil at 4°C for four days. The experiments were all performed in silicone oil and within an hour at room temperature. The observed stress-strain curve for pig menisci was sigmoid and this was proved to be due to its net-like framework of collagenous fibres by wide angle X-ray diffraction and stress relaxation experiments. Youngs modulus was calculated from the linear part of stress-strain curve showing 1.75 × 10 8 dyn/cm 2 with 1.7%/sec strain rate. The strain rate dependency of Youngs modulus increased very slightly. This is contrary to the suggested idea that the meniscus could mainly play a role of a shock absorber in the knee joint. Stress relaxation tests with tensile load revealed no difference in visco-elastic properties between human normal and torn menisci.

Observation of molecular orientation in evaporated films of n-paraffins

Abstract Molecular orientation, its distribution and long periods of n -paraffin thin films evaporated on glass substrate were measured by an energy dispersive X-ray diffractometer. The number of crystallites whose c ∗ axes are normal to the glass substrate (normal orientation) increases with temperature up to the temperature at which a phase transition to a disordered state occurs in ordinary paraffin crystals. This orientational change was observed to be an irreversible process. The orientational distribution has a narrow peak with a full width at half-maximum of less than 0.1° around normal orientation even in as-evaporated films. Its population around normal orientation is increased by heating to be about three times as high as that of the as-evaporated films. This is the first report on accurate observations of the orientational distribution in evaporated thin films.

Annealing effects on molecular orientation in evaporated films of n-paraffins

Abstract The time variation in the X-ray intensities of the 006 and 110 reflections from n- C33 H68 films evaporated on glass substrates was investigated in order to elucidate the mechanism of reorientation of molecular chains during the annealing process. The experimental results revealed that the number of molecules oriented normally to the substrate increases with annealing time, while the number with lateral orientation decreases at a different rate. Further data analysis suggested that this molecular reorientation proceeds via groups consisting of about four molecules when they acquire simultaneously a thermal energy comparable to that of fusion.

Pressure effect on phase transition in ferroelectic polymers

Abstract Pressure effects of phase transition behaviour in two kinds of ferroelectric polymers of poly(vinylidene fluoride), PVDF, and copolymers of vinylidene fluoride and trifluoroethylene, (VDF/TrFE), are discussed. In the case of PVDF, several high-pressure treatments including a high-pressure annealing and a uniaxial compression were shown to induce a crystal transformation from a non-polar Form II crystal to a polar Form I crystal, which has ferroelectric characteristics and high piezoelectric activity. In addition, substantial pressure effects on ferroelectric phase transition points as well as crystal structures were observed for (VDF/TrFE) copolymers with different VDF contents. The most significant pressure effects were observed for copolymer samples with unstable ferroelectric structures at atmospheric pressure. From high-pressure X-ray and Raman scattering studies, these pressure effects were suggested to originate from the pressure-induced conformational transition from gauche to trans in the...

Precise evaluation of fast fracture velocities in acrylic polymers at the slow-to-fast transition

Transient fast fracture velocities at the onset of the slow-to-fast transition in polymethylmethacrylate (PMMA) have been measured precisely in single-edge-notched specimens of various geometries by using ultrasonic fractography. Little sign of the fracture velocity of the order of 10° m sec−1 have been detected on the instability onset. The fast fracture starts from a point source almost instantaneously. The initial velocity has been shown to fall in a small range, 90 to 150 m sec−1, almost independent of the loading speeds from 0.1 to 100 mm min−1 and specimen temperature from −50 to 40° C, with exceptional cases for specimens loaded slowly (0.1 mm min−1) at a low temperature (−50° C). As the final minimum velocity of an arresting crack, a value of 42 m sec−1 has been obtained under room temperature. Crack propagation in low molecular weight PMMA has been shown to be more temperature, as well as loading rate, dependent than in higher molecular weight PMMA.

Direct observation of the growth process of organic crystals by scanning tunnelling microscopy

Abstract STM (scanning tunnelling microscope) observation was conducted on n-paraffin molecules (n-C 33 H 68 ) adsorbed on a graphite substrate. A series of the STM images could reveal each of the progressive stages of the crystal growth, suggesting how the molecules grow into two-dimensional crystals.

X-ray microanalysis and acoustic emission studies on the formation mechanism of secondary cracks in PMMA

The formation mechanism of secondary cracks in poly(methyl methacrylate) (PMMA) was investigated using various methods. X-ray element analysis and SEM observations on parabolic markings showed that there exist certain defects such as silicon compound and microcracks at their foci, forming the potential sources for the secondary cracks (a static factor). On the other hand, the fracture process was monitored simultaneously with acoustic emission (AE) and high speed shadow-optical techniques. These observations revealed that density of the parabolic marking has a closer correlation to the amplitude of the stress wave emitted during crack propagation, rather than to the values of crack speed or stress intensity factor (a dynamic factor). The formation mechanism is thus explained by the combination of these static and dynamic factors.