| POLYMERS Vol.65 No.5 |
| >> Japanese | >> English |
COVER STORY
Origin of Polymer Science and Technology : Rubbery State |
| COVER STORY: Highlight Reviews |
| Large Deformation Behavior of Polymer-Network Based Soft Materials | Kenji URAYAMA |
| <Abstract> High elasticity of rubbers and gels is a unique property resulting from the entropic elasticity of flexible polymer networks. Unequal biaxial stretching provides valuable information about large deformation characteristics. It reveals that the Tetra-PEG gels, which is a model network with uniform structure without trapped entanglement, have a finite degree of explicit cross-effect of strains on stress in contrast to the expectation of classcal theories of rubber elasticity for ideal networks. It also shows that the slide-ring gels, whose cross-links are movable along the network strands, exhibit a minimal degree of cross-effect of strains which stems only from the volume conservation. It demonstrates that the low-density elastomer foams with finite compressibility exhibit considerably weak cross-effect of strains. A recent study on the crack growth dynamics in filled elastomers is also highlighted. The profiles of the crack tips at various tearing energy are analyzed on the basis of weakly nonlinear elasticity theory for fracture mechanics. Keywords: Elastomers / Rubber / Gels / Foams / Elasticity / Fracture / Polymer Networks |
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| Rheology of Rubber on Glass Transition | Yoshihisa MIYAMOTO |
| <Abstract> Rubbers show a variety of deformation modes depending on temperature and a rate of deformation. This article presents the static strain dependence of linear viscoelasticity under large uniaxial deformation on rubber-glass transition and the stress-strain relation followed by stress relaxation near the glass transition temperature. Keywords: Rubber / Glass Transition / Linear Viscoelasticity / Strain Dependence / Stress-Strain Curve / Stress Relaxation |
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| Hierarchical Network Structures in Filled Rubbers | Yoshinobu ISONO |
| <Abstract> Filled rubbers are mixtures of polymers having low glass transition temperatures and inorganic fillers such as carbon black and silica. Their high moduli and high strength are based on hierarchical networks due to polymer-polymer, polymer-filler, and filler-filler interactions. Crosslinking points have been considered to be found fairly homogeneously in crosslinked polymers, but have been observed to exist inhomogeneously and the extensional strength of crosslinked natural rubber is due to full-stretch of fairly short network-chains. In addition, dangling chains are found to exhibit energy dissipation of crosslinked networks. Change in the contact filler network exhibits remarkable strain- and/or strain-rate-sensitive nonlinear viscoelasticity. Meanwhile, high strength of filled rubbers is based on extension of rather short chains bridging adjacent filler particles in bridged filler networks as in the case found in a crosslinked network. Keywords: Rubber / Filler / Crosslink / Hierarchical Networks / Inhomogeneity / Nonlinear Viscoelasticity / Entropy Elasticity / Energy Elasticity |
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| COVER STORY: Topics and Products |
| New Concept in Strain-Induced Crystallization of Natural Rubber | Masatoshi TOSAKA |
| <Abstract> Despite the long history of studies, a quantitative theory on strain-induced crystallization of natural rubber has not been fully established. All the theories so far have considered the entropy change due to extension as the only factor to enhance crystallization. We obtained experimental data about the dependence of crystallization rate on stretch ratio. The results were compared with theoretical calculations based on the previous concept regarding the entropy change as the only factor. However, the theoretical calculations were totally inconsistent with the experimental results. The origin of this discrepancy was found to be the calculated high activation energy of nucleation even after the entropy change due to extension was considered. This quantitative comparison indicated that the reduced surface free energy due to the formation of bundle-like nuclei is the additional factor to enhance crystallization. Furthermore, it was revealed that surface energies have a greater effect on the decrease of the activation energy than the entropy change by extension. Keywords: Nucleation / Crystallization Rate / Rubber Elasticity / Surface Free Energy / Crystallite Size / Stretch Ratio |
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| Coase-Grained Simulations for the Development of Rubber Materials | Hiroshi MORITA |
| <Abstract> The simulation studies of the rubber materials using coarse-grained simulations are described. In these studies, we focus on the analysis of rubber materials. The coarse-grained molecular dynamics method is applied to simulate the elongated structure of rubber materials. In the elongated structure, the expanded bonds can be analyzed, and the bond-lines, which is the origin of the stress of elongated rubber, can be obtained in our analysis. Using self consistent field simulation, the end segment distributions in the filler filled materials are estimated. From our simulations, the segregation of the end segment at the interface of filler can be found. The information derived from the coarse-grained simulations will be important to develop the next generation of rubber materials, and in the near future, further analysis techniques to analyze the rubber materials will be developed. Keywords: Coarse-Grained Simulation / OCTA / MD / SCF |
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| Tructure of Crosslinking Junctions and Properties of Vulcanized Natural Rubber | Seiichi KAWAHARA |
| <Abstract> Crosslinking junction as a constituent may play an important role in mechanical properties of rubbers and gels. This may be analyzed by field gradient-fast-magic angle spinning (FG-FMAS) NMR spectroscopy, which is developed to eliminate effect of dipole-dipole interaction for the rubbers and gels. The FG-FMAS NMR spectroscopy enabled to apply various pulse sequences such as DEPT, APT, HETCOR, HMQC, HSQC and HMBC to the vulcanized natural rubber; so that, it makes possible to determine the structure, positively. Here, a structural analysis of the crosslinking junctions of vulcanized natural rubber is described in terms of not only 1D-NMR method but also 2D-NMR method. The structure of crosslinking junctions is found to be dependent upon accelerator. The outstanding mechanical properties of vulcanized natural rubber are related to the structure of the crosslinking junctions. Keywords: Natural Rubber / Vulcanization / Crosslinking Junction / Solid State NMR / Field Gradient-Magic Angle Spinning / 2D-Measurement / Stress-Strain Curve / Tensile Strength |
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| Polymer Science and I: A Personal Account |
| My Experience of Working Abroad | Shinichiro KAWANO |
| <Abstract> After working as a postdoctoral fellow at the Max Planck Institute for Polymer Research in Mainz, Germany, I have learned about the importance of not only doing presentations in English but also making fruitful connections with researchers of very different backgrounds. This short article describes what I experienced and how I struggled abroad. |
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| Front-Line Polymer Science |
| Current Polyurethane Science | Ken KOJIO |
| <Abstract> Polyurethane studies has been still fascinating to us. In this review, current polyurethane science has been addressed focusing on structure-properties relationship of polyurethane with controlled primary strcutre, structure analysis using synchrotron radiation x-ray diffraction and scattering, development of polyurethane withself-healing properties, environment friendly polyurethanes. It is expected that polyurethane would give new brand properties by studies combining analysis based on synchrotron radiation x-ray and simulation. Keywords: Polyurethane / Primary Structure / Synchrotron Radiation X-ray / Self-Healing / Environmental Friendly / Elastomer |
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