On the Dynamic Mechanical Properties of Polymers at Ultrasonic Frequencies in Relation to Their Glass Transition Phenomena

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Complex Young's modulus, rigidity and bulk modulus are measured at 33kc/s, 66kc/s and 1Mc/s for polystyrene, polymethyl methacrylate, polyvinyl acetate and phenol resin. In each material, the storage modulus-temperature curve has a discontinuity in the slope, irrespective of frequency and type of modulus, at the glass transition temperature T_g determined from thermal expansion. This discontinuity takes place through a strong dependence of the modulus on the specific volume. Besides, the first three materials exhibit secondary discontinuities at T_g', about thirty degrees below T_g both in thermal expansion and modulus-temperature curve. Some possible interpretations are given to this secondary discontinuity, resulting in the conclusion that the glass transition occurs over a rather wide range of temperature and is completed at T_g with increasing temperature. The ratio of the temperature coefficients of the modulus, taken below and above T_g, agrees well with that of volume expansion curve. This is also the case about T_g', being indicative of predominantly energetic nature of elasticity. The loss factor begins to rise slightly at T_g', then rapidly at T_g as the temperature is elevated, suggesting that local motions of molecular chains are first encountered at T_g'. The real part of Poisson's ratio seems nearly constant through the temperatures studied, including the glass transition temperature, where as the imaginary part is found to vanish.
社団法人日本物理学会の論文
1959-08-05

On the Dynamic Mechanical Properties of Polymers at Ultrasonic Frequencies in Relation to Their Glass Transition Phenomena

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