Take the 2-minute tour ×
Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free.

I am reading in some book: "The glass transition is similar in appearance to a second-order phase transition, but it is not a true thermodynamic phase transition. This is because the transition temperature depends on the rate at which we do the experiment."

What's the matter with that rate? Is it only a question of mathematical definition of thermodynamic phase or is there any physical reason to exclude rate-dependent transitions?

share|improve this question

1 Answer 1

up vote 1 down vote accepted

Thermodynamic phase transitions are defined as discontinuities in (derivatives) of the free energy. Thus, they are about differences in equilibrium properties, even though often we end up measuring a non-equilibrium property because it's easier. But nowhere in this framework does a rate-dependent, i.e. non-equilibrium, situation occur, and therefore the glass transition is not a "proper" phase transition in that sense.

share|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.