On Poisson's ratio of glass and liquid vitrification characteristics

Abstract

The apparent activation energy for viscous flow of a glass-forming liquid, Ea , and its ratio to temperature Tf , mf (= Ea /2.3Tf ), are seen as a measure of the viscosity's departure from the Arrhenius equation. As the viscosity, η, increases on cooling, Ea and mf increase. On slow cooling, a liquid vitrifies at a lower T, higher η and higher mf , and on rapid cooling it vitrifies at a higher T, lower η and lower mf . 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 mf increases. Available data on structural relaxation of metal alloy glasses confirm it. Therefore, as a glass spontaneously becomes denser with time, mf 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 Tg 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.