On Poisson's ratio of glass and liquid vitrification characteristics

Abstract

The apparent activation energy for viscous flow of a glass-forming liquid, E_a , and its ratio to temperature T_f , m_f (= E_a /2.3T_f ), are seen as a measure of the viscosity's departure from the Arrhenius equation. As the viscosity, η, increases on cooling, E_a and m_f increase. On slow cooling, a liquid vitrifies at a lower T, higher η and higher m_f , and on rapid cooling it vitrifies at a higher T, lower η and lower m_f . It is argued that Poisson's ratio, υ _Poisson , and the instantaneous bulk modulus to shear modulus ratio, K _∞/G _∞, of a liquid (and glass) would decrease as it departs from Arrhenius behaviour or m_f increases. Available data on structural relaxation of metal alloy glasses confirm it. Therefore, as a glass spontaneously becomes denser with time, m_f increases and its state becomes dilationally stiffer. This finding is opposite to the correlation that, amongst glass-forming liquids of different chemical compositions, υ _Poisson and K _∞/G _∞ increase when departing from Arrhenius behaviour at T_g or m increases (V.N. Novikov and A.P. Sokolov, Nature 431 961 (2004)). Further analysis shows that a liquid's structure has a predominant effect on its elastic constants.

Acknowledgements

The author is grateful to the Natural Sciences and Engineering Research Council of Canada for support of his general research through a Discovery Grant.