TY - JOUR
T1 - Glass-formers and viscous liquid slowdown since David turnbull
T2 - Enduring puzzles and new twists
AU - Angell, Charles
N1 - Funding Information:
Our work on the glass transitions in inorganic and molecular glass-former systems has been continuously supported by the Solid State Chemistry Division of the NSF–DMR, which we acknowledge with great appreciation. Recently, the support of “all-or-nothing” processes in water-like systems and their link to biological processes of the same character have been supported by the Chemistry Division of NSF under the Collaborative Research in Chemistry program. The author acknowledges with pleasure the stimulating interactions with colleagues Pablo Debenedetti, Peter Rossky, and Gene Stanley that this program has encouraged. The recent interaction with a theorist colleague at ASU, Dmitry Matyushov, has been very fruitful, and many examples of its consequences have been included in the text. Finally, the author is indebted, and unceasingly grateful, to the many clever and diligent co-workers (too many to mention by name, although many are present in the bibliography) with whom he has had the pleasure of collaborating over the many pleasant years in which this subject of glass-formers and their intriguing properties has been developing.
PY - 2008/5
Y1 - 2008/5
N2 - To Turnbull's study of the kinetic problem of nucleation and growth of crystals, we add the further enquiry into what lies behind the slow nucleation kinetics of glass-formers. Our answer to this question leads to the proposal of conditions in which a pure liquid metal, monatomic and elemental, can be vitrified. Using the case of high-pressure liquid germanium, we give electron microscope evidence for the validity of our thinking. On the question of how liquids behave when crystals do not form, Turnbull pioneered the study of glass transitions in metallic alloys, measuring the heat capacity change at the glass transition Tg for the first time, and developing with Cohen the free volume model for the temperature dependence of liquid transport properties approaching Tg. We extend the phenomenological picture to include networks where free volume does not play a role and reveal a pattern of behavior that provides for a classification of glass-formers (from "strong" to "fragile"). Where Turnbull studied supercooled liquid metals and P4 to the homogeneous nucleation limit using small droplets, we studied supercooled water in capillaries and emulsions to the homogeneous nucleation limit near -40°C. We discuss the puzzling divergences observed that are now seen as part of a cooperative transition that leads to very untypical glass-transition behavior at lower temperatures (when crystallization is bypassed by hyperquenching). Finally, we show how our interpretation of water behavior can be seen as a bridge between the behavior of the "strong" (network) liquids of classical glass science (e.g., SiO2) and the "fragile" behavior of typical molecular glass-formers. The link is made using a "Gaussian excitations" model by Matyushov and the author in which the spike in heat capacity for water is pushed by cooperativity (disorder stabilization of excitations) into a first-order transition to the ground state, at a temperature typically below Tg. In exceptional cases like triphenyl phosphite, this liquid-to-glass first-order transition lies above Tg and can be studied in detail.
AB - To Turnbull's study of the kinetic problem of nucleation and growth of crystals, we add the further enquiry into what lies behind the slow nucleation kinetics of glass-formers. Our answer to this question leads to the proposal of conditions in which a pure liquid metal, monatomic and elemental, can be vitrified. Using the case of high-pressure liquid germanium, we give electron microscope evidence for the validity of our thinking. On the question of how liquids behave when crystals do not form, Turnbull pioneered the study of glass transitions in metallic alloys, measuring the heat capacity change at the glass transition Tg for the first time, and developing with Cohen the free volume model for the temperature dependence of liquid transport properties approaching Tg. We extend the phenomenological picture to include networks where free volume does not play a role and reveal a pattern of behavior that provides for a classification of glass-formers (from "strong" to "fragile"). Where Turnbull studied supercooled liquid metals and P4 to the homogeneous nucleation limit using small droplets, we studied supercooled water in capillaries and emulsions to the homogeneous nucleation limit near -40°C. We discuss the puzzling divergences observed that are now seen as part of a cooperative transition that leads to very untypical glass-transition behavior at lower temperatures (when crystallization is bypassed by hyperquenching). Finally, we show how our interpretation of water behavior can be seen as a bridge between the behavior of the "strong" (network) liquids of classical glass science (e.g., SiO2) and the "fragile" behavior of typical molecular glass-formers. The link is made using a "Gaussian excitations" model by Matyushov and the author in which the spike in heat capacity for water is pushed by cooperativity (disorder stabilization of excitations) into a first-order transition to the ground state, at a temperature typically below Tg. In exceptional cases like triphenyl phosphite, this liquid-to-glass first-order transition lies above Tg and can be studied in detail.
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U2 - 10.1557/mrs2008.108
DO - 10.1557/mrs2008.108
M3 - Article
AN - SCOPUS:44949256284
SN - 0883-7694
VL - 33
SP - 544
EP - 555
JO - MRS Bulletin
JF - MRS Bulletin
IS - 5
ER -