Steady plastic flow in specimens of tightly cross-linked glassy epoxy network was analyzed as a rate process to discuss the mechanism of nonlinear viscoelastic behavior of glassy network polymers under large deformation. Specimens were uniaxially stretched at temperatures below the glass transition temperature with various strain rates. True stress σ and birefringence in the specimen were recorded during the deformation as functions of nominal strain εn. The glassy stress σG was extracted from the σ-εn relations by means of modified stress-optical rule (MSOR). The obtained σG-εn relations had a steady flow region, which was observed as an almost constant stress state in the post-yield strain range. The flow stress in this region was analyzed by using the Eyring equation in a special way proposed by Nanzai. The analysis gave an experimental relation between the activation enthalpy ΔH and the activation entropy ΔS, which agreed fairly well with that derived from WLF equation for the linear viscoelastic relaxation of the material in the molten state. This agreement provides an experimental evidence verifying structural change of the glass into liquid-like, highly non-equilibrium structure in the glassy network polymer under large deformation. Independently of the presence of crosslinked molecular structures, the essential mechanism of nonlinear viscoelasticity of glassy polymers is found to be strain-induced structural change.
We studied the feature of poly(ethylene oxide) crystallization under a temperature gradient. Annealing time dependence on d-spacing and orientation of crystalline lamellae for samples crystallized under the temperature gradient was examined by using small-angle X-ray scattering. For this purpose, annealing times of 1 hour and 43 hours to maintain the temperature gradient (hotter side 55℃ and cooler side 35℃) were selected as a parameter to study. Also, we observed the position of crystallization front under the temperature gradient and evaluated the rate of the growth front of crystalline region under the temperature gradient in order to compare with the result for the case of the isothermal crystallization.
In this article the slipping of less entangled polyisobutylene (PIB) melts and solutions in shear is investigated by the damping as well as the stress growth behavior. The obtained data are also compared with those of the moderately and highly entangled PIB systems. The concentrated solutions do not show the slipping at the sample-fixture interface probably because the stress level on the stress-strain curves is very low even at large preset strains. The less entangled melts do not show strong damping, although they show a stress peak whose value amounts to the critical stress of the moderately and highly entangled PIB samples. It is suggested that little slipping occurs for the melts of the less entangled PIB due to the existence of the fast stress relaxation processes.
Polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) diblock copolymer used in this study was synthesized by living anionic polymerization. The vinylpyridine units in PS-b-P2VP were partially quaternized by 1-bromobutane and the degree of quaternization was controlled in reaction time. The thin filmsof the quaternized diblock copolymer (PS-b-qP2VP) were prepared by spin-coating onto silicon wafers. Subsequently, the films were thermally annealed in a vacuum for given time. The influence of quaternization degrees on the formation and orientation behavior of the phase separated structure (hexagonally packed cylinders) was investigated by grazing incidence small angle X-ray scattering. For as-cast film, the structure in the thin film was disordered and the highly ordered and oriented phase separated structure appeared after thermal annealing. Annealing time to reach the stable structure depended on degree of quarternization and the thin film with high quaternization required a longer annealing time for rearrangement, which might be caused by the qP2VP anchoring on silicon wafers with specific interaction. The ordered cylindrical micro-domains (qP2VP) in the PS-b-qP2VP thin films was found to align parallel to the substrate, respectively. In case of high quaternization, not only parallel cylinders but also other morphology was mixed, or completely different morphology e.g. hxagonally perforated lamellar structure and spherical morphology might form.
We newly developed amorphous polyvinyl alcohol resin derivative having the side chain 1,2-diol bond in order to achieve both melt property and good gas barrier property. Solid-state NMR measurement of this polyvinyl alcohol resin derivative showed a component with longer relaxation time in the amorphous phase than that in the crystalline phase. The lamellar thickness of the amorphous polyvinyl alcohol resin derivative was getting decreased according to content of the 1,2-diol bond in side chain. Nevertheless, its density got high. We think that this phenomenon is attributed to the dense amorphous phase. As a result, we think that the melt property and gas barrier property of the amorphous polyvinyl alcohol resin derivative will be improved compared to those of the normal homo polyvinyl alcohol.
Mechanical properties at low temperature (-180℃~RT) of polyethylene (PE) were investigated. Charpy impact strength of Ultra-high molecular weight polyethylene (UHMWPE) was much higher than that of HDPE. From dynamic mechanical analysis result, they had the γ relaxation at around -120 ℃, but the intensity of the peak of UHMWPE was much higher than that of HDPE. Moreover, when taking the result that they had almost the same degree of the crystallinity into consideration, mechanical properties at low temperatures of PE were influenced by not only the molecular weight but also the molecular motion at low temperature regions of PE. When the samples were prepared by stacking inflation-films of UHMWPE, HDPE, and their blends, it was found that Stacking Inflation Blend-film sample (SIB) had the better mechanical properties at low temperatures in comparison with the other blend samples, especially for Direct Molding sample (DM). This result indicated that mechanical properties at low temperatures of PE were influenced by the preparation methods of the samples. Furthermore, the rheological dissipation energy derived from the γ relaxation of the samples showed the good liner correlation with the Charpy Impact strength at -100 ℃, indicating that the molecular motion of PE at low temperature region affected the mechanical properties of PE. Finally, it was found that UHMWPE which had the highest mechanical properties at low temperature region had the smallest anharmonicity of all samples, and HDPE which had the poorest mechanical properties at the same region had the highest anharmonicity, and SIB and DM samples had the intermediate values of them. Therefore, it was deduced that anharmonicity of a polymer could also affect the mechanical properties at low temperatures of the polymers.
Microdomain structures formed in the mixture of polystyrene-b-polyisoprene (SI) diblock copolymer, whose number-averaged molecular weight, Mn, and volume fraction, ƒPS are, respectively, 45,000 and 0.70, with a polyisoprene homopolymer (PI, Mn = 18,000) and dioctyl phthalate (DOP) were studied by the singular value decomposition (SVD) of small-angle X-ray scattering. The volume ratio of SI/PI/DOP was 43.7/16.3/40 vol.%. SAXS measurement was performed on the mixture every 20 ℃ from 130 to 30 ℃ in a cooling cycle and successively every 20 ℃ from 30 to 130 ℃ in a heating cycle. The scattering observed at the corresponding temperatures in both of the cycles were in good agreement. The scattering measured at 130 ℃ had multiple peaks; the relative peak position ratios to the primary peak was close to 1 : √8/6 : √14/6 : √16/6 : √20/6 : √22/6 that are typical to an ordered bicontinuous double gyroid (OBDG) structure, while the one at 30 ℃ had multiple peaks; the relative peak position ratios to the primary peak were 1 : √3/2 : √4/2 : √6/2 : √8/2 typical to an ordered bicontinuous double diamond (OBDD) structure. The scattering at the intermediate temperatures from 50 to 110 ℃ showed more complex multiple peaks. The SVD was conducted on the set of the SAXS profiles: The rank was 6 but the first two singular values were significantly larger than the rest of the four values. Thus, the low-rank approximation with the first two singular values was employed. All of the temperature dependent SAXS were successfully rebuilt with the first two basis functions obtained by SVD. The weighting functions used to reconstruct the profiles relate to the first two singular values; the second weighting function relating to the temperature change of the SAXS showed only one drastic change between 70 and 90 ℃. This means that no intermediate structure between OBDD and OBDG exists. The fraction of OBDD was also calculated by the temperature change in SAXS: 0.98, 0.85, 0.28 and 0.11 at 50, 70, 90 and 110 ℃, respectively.
Thick high temperature components in thermal power plants such as turbine rotors are subjected to creep-fatigue loading under cycles of start - steady state - stop operation. The creep-fatigue damage gradually proceeds in these components. Therefore it is important to clarify damage extension mechanism under the creep-fatigue loading to develop accurate life assessment methods for reliable operation. In this study, a stress control creep-fatigue test with 10 minutes stress hold time at the maximum stress was conducted in a scanning electron microscope to clarify void growth behavior during the test. A strain control creep-fatigue test with 5 hours strain hold was also performed to observe void initiation and growth condition by interrupting the tests. From the observation, round shape voids initiated around 15% of the life and grew by changing the shape to a crack-like, and rate of void growth is considered to be accelerated by cyclic loading based on the fact that size of the maximum void under the creep-fatigue loading is larger than that under the static creep loading. According to the observation results, the previous proposed void growth rate equation was multiplied by acceleration factor. The acceleration factor is assumed to be dependent on applied strain range. The maximum void growth behaviors under both the stress and strain creep-fatigue loadings were accurately predicted by the extended void growth simulation procedure to the creep-fatigue loading considering influence of hold time on the acceleration factor.
The residual strain of 23Cr-45Ni-7W Alloy welds was estimated by the change in the dislocation density and the average misorientation within grains. X-ray diffraction was used to measure the dislocation density by the modified Williamson-Hall method and the modified Warren-Averbach method. EBSD technique was used to measure the orientation in order to calculate the grain orientation spread (GOS) as the average misorientation within grains. Tensile tests were conducted at room temperature and were interrupted to prepare a number of specimens with different residual strain. The changes in the dislocation density and GOS with the strain were investigated using the interrupted specimens and the heat-affected zone in 23Cr-45Ni-7W Alloy welds. The dislocation density and GOS increased approximately linearly with increase in the residual strain. The residual strain of the heat-affected zone in 23Cr-45Ni-7W Alloy welds was evaluated from the linear relationships. The residual strain near the bond line estimated by the dislocation density was 3.7%;the estimated residual strain decreased with increases in the distance from the bond line. At 10 mm away from the bond line, the residual strain became less than 1%. The change in the residual strain near the bond line estimated by GOS showed a similar tendency.
This paper reviews physical properties and device applications of oxides, especially corundum-structured oxides. Oxides had been considered as unwelcome interruptions in puddling cupper or iron at first. However, after the invention of barium titanate, it begun to attract attentions for their varied functions. As well as an evolution of fabrication techniques and equipment, it could be realized to fabricate high-quality oxide thin films free from impurities. Various physical functions in oxides have been unraveled. Furthermore, in these days, meta-stable oxides can be grown under atmosphere at low temperature by mist CVD method. Corundum-structured oxides has been gathering much attentions for these abilities for electrical device applications.