高分子レオロジーに対する私見 : レオロジー特集号

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Rheological studies on highpolymers have made great progress in recent years, and have obtained a number of excellent results which are being systematized into well refined theories. For instance, the development of the methods for the measurement of relaxation spectra covering a very side range of time-scale and the establishment of the meaning of spectra are among the outstanding fruits of recent rheological studies on highpolymers, and, so far as the amorphous substances are concerned, the relaxation spectrum supplements a new description of property which is characteristic to the material. However, we are now in the position to pay attention to the fact that the recent development of the knowledge on the fine structure of materials have little been introduced into the analysis of the mechanical properties of the materials. As a matter of fact, in the rheological studies hitherto, the states of materials are only very roughly classified into a few simple types, such as amorphous, crystalline, and mixed system of amorphous and crystalline phases. This formal simplicity has helped thus far the development of rheological studies, but it is now desired to treat the problems from the more real standpoint of view. This we pointed out five years ago at the 5th Symposium of Rheology of Japan (November, 1956), and showed as examples some of the results of "photo-viscoelastic" studies which had been commenced by us earlier. In these studies the change in birefringence could be measured at the same time as stress and strain. Recently Utsumi supplemented a work with the thin films of slightly vulcanized rubber, which are thought to behave in comformity to the theory of rubber elasticity. According to the theory, it is expected that the birefringence decreases with time in proportion to the relaxation of stress. This is true only in the case of smaller extension, for the theory does not hold in the case of higher extension, as can be seen in Fig. 1. In the latter case the stress relaxes as rapidly as ever, but the change in birefringence becomes smaller, and finally, at a greater extension, it increases with time contrary to the stress. Therefore, the change in birefringence gives us information about the threshold elongation, over which the deformation begins to deviate from the rubber elasticity. The increase in the birefringence with time will mean the spontaneous orientation or crystallization of the stretched rubber molecules, which results in the spontaneous contract of the cross-sectional area of the material. This is one of the origins of stress relaxation. Therefore, the relaxation at a higher extention is not purely caused by the entropy change. In fact, the film which is stretched to a high extent shows the sharp spots due to the crystallites in the x-ray diffraction pattern, as shown in Photo. 1. But for the simultaneous measurements of birefringence, which gives a measure of inner structure of material with respect to the molecular orientation, the stress relaxation at the higher extension could not be distinguished from the usual rubber elastic phenomenon.
社団法人日本材料学会の論文
1962-05-15

著者

堀尾正雄
京都大学工学部

高分子レオロジーに対する私見 : レオロジー特集号

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