GLASS-FORMING LIQUIDS, ANOMALOUS LIQUIDS, AND POLYAMORPHISM IN LIQUIDS AND BIOPOLYMERS

Glass formation in nature and materials science is reviewed and the re cent recognition of polymorphism within the glassy state, polyamorphis m, is discussed. The process by which the glassy state originates duri ng the continuous cooling or viscous slowdown process, is examined and the three canonical characteristics of relaxing liquids are correlate d through the fragility. The conversion of strong liquids to fragile l iquids by pressure-induced coordination number increases is discussed, and then it is shown that for the same type of system it is possible to have the same conversion accomplished via a first-order transition within the liquid state. The systems in which this can happen are of t he same type which exhibit polyamorphism, and the whole phenomenology can be accounted for by a recent simple modification of the van der Wa als model for tetrahedrally bonded liquids. The concept of complex amo rphous systems which can lose a significant number of degrees of freed om through weak first-order transitions is then used to discuss the re lation between native and denatured hydrated proteins, since the latte r have much in common with plasticized chain polymer systems. Finally, we close the circle by taking a short-time-scale phenomenon given muc h attention by protein physicists, viz., the onset of an anomaly in th e Debye-Waller factor with increasing temperature, and showing that fo r a wide variety of liquids, including computer-simulated strong and f ragile ionic liquids, this phenomenon is closely correlated with the e xperimental glass transition temperature. This implies that the latter owes its origin to the onset of strong anharmonicity in certain compo nents of the vibrational density of states (evidently related to the b oson peak) which then permits the system to gain access to its configu rational degrees of freedom. The more anharmonic these vibrational com ponents, the closer to the Kauzmann temperature will commence the expl oration of configuration space and, for a given configurational micros tate degeneracy, the more fragile the liquid will be.