Liquid Fragility and the Glass Transition in Water and Aqueous Solutions C. A. Angell Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona 85287-1604 Received September 18, 2001 Contents I. What Is the Glass Transition? What Is the Fragility of a Liquid? 2627 II. The Glass Transition in Aqueous Solutions, and in Water 2628 (a) Glasses from Aqueous Solutions 2628 (i) Electrolyte Solutions 2628 (ii) Nonelectrolyte Solutions 2629 (iii) Solution Glasses Formed Using the Pressure Variable 2630 (iv) Solution Glasses Formed by Nonliquid Routes 2631 (v) Relation of Glass Transition to Liquid Properties 2632 (b) Glassy Water 2632 (i) The Glass Transition Temperature of ASW, and Its Relatives 2632 (ii) Polyamorphism: High and Low Density Glasses of Water 2636 (iii) Vitreous Polymorphs by Demixing from Aqueous Solutions 2637 III. Fragility of Aqueous Solutions and Water 2637 (a) Liquid and Solution Fragility 2637 (b) Electrolyte Solutions 2640 (i) Complex Systems with Fragile/Strong Crossovers 2640 (ii) Simply Behaving Systems 2641 (c) Nonelectrolyte Solutions 2641 (d) Models for the Fragility 2643 (e) Fragility of Pure Water 2645 IV. Concluding Remarks 2646 V. Acknowledgments 2647 VI. References 2647 I. What Is the Glass Transition? What Is the Fragility of a Liquid? In a review of the present title, the first require- ment is to ensure that the title words are understood. While the term “glass” is broadly familiar, and the origin of the “glass transition” in terms of the crossing of system and experimental time scales is generally agreed upon, there are at least three different defini- tions of the material property “glass transition tem- perature” (T g ) in current use. 1,2 Furthermore, these may differ from each other by as much as 50 K in certain higher T g cases. The difference is a conse- quence of the magnitude of the “glass transformation range” within which the T g is variously defined. This magnitude, the “width of the glass transition”, can vary greatly from system to system, for reasons discussed below. Since the quantity T g will recur frequently in this review, it is necessary to deal adequately with the definition problem, and this will be done by reference to Figures 1 and 2 below. Depending on the liquid in question, glass transi- tions may be observed occurring over an enormous range in temperature, from below 50 K to above 1500 K. The reason for this range is clearly to do with the strength of the interparticle interactions, i.e., the “bonds” that are being broken as the particles rear- range. However, the reason that some glass transi- tions are “sharp” (meaning narrow glass transfor- mation range, or “transition width”) and others very spread out in temperature is not so clear. It is largely to do with the “fragility” of the glassformer, but may C. A. Angell was born in Canberra, Australia, and studied chemistry and metallurgy at the University of Melbourne. After working on molten salts with J. O’M Bockris at the University of Pennsylvania for two years, he became the Stanley Elmore Fellow at Imperial College of Science, London, where he completed his Ph.D. under the direction of John W. Tomlinson. There he was awarded the Armstrong medal for graduate research 1959- 1961. He returned to Australia as lecturer in chemical metallurgy but after two years came back to the U.S. as a post-doc with Dieter Gruen at Argonne National Laboratory. In 1966, he joined Purdue University as Assistant Professor, becoming full Professor in 1971. In 1989, he moved to Arizona State University where he is now Regents’ Professor of Chemistry and Biochemistry. He has enjoyed and profited from sabbatical leaves at the University of Amsterdam, the Australian National University, Institute Laue-Langevin, Grenoble, the Ecole de Physique et Chemie Industrielle, Paris, University of Rennes-Beaulieu, Sydney University, and the University of Rome. His research interests range from rechargeable lithium batteries and fuel cells, through the phenomenology of the glass transition and the origin of fragility in liquids, to the anomalous properties of water and geochemical fluids and their relation to polyamorphism. Currently, he is focusing on the annealing behavior of hyperquenched liquids and solutions, particularly denatured protein solutions, with a sideline on nanoporous network glasses as gas storage media. 2627 Chem. Rev. 2002, 102, 2627-2650 10.1021/cr000689q CCC: $39.75 © 2002 American Chemical Society Published on Web 07/30/2002