Thermodynamic cooperativity in glass-forming liquids: Indications and consequences

From our recent studies on crystal melting, a small-liquid-nucleus scenario is concluded. On this basis, a thermodynamic cooperativity is proposed to be the number of atoms in a liquid nucleus, which may serve as an upper limit for the kinetic cooperativity. Preliminary applications of the concept of a thermodynamic cooperativity in elucidating several significant features of glass-forming liquids are promising. In this work, efforts are devoted for a detailed examination of the existence of the suggested thermodynamic cooperativity by exploring a variety of research results on crystal melting, gas condensation, and liquids, specifically, in a logical chain of reasoning, (i) whether vacancies may dominate the high-temperature properties of crystals, (ii) whether liquid nucleation may be initiated from vacancies, and (iii) whether the liquid nucleus may be very small. In addition, successful applications of the concept of a thermodynamic cooperativity are briefly reviewed, lending further supports to its existence.