CiteULike: dchens Angell

Relaxation in glassforming liquids and amorphous solids

CA Angell — 2007-09-19T18:39:48-00:00

Journal of Applied Physics, Vol. 88, No. 6. (2000), pp. 3113-3157.

The field of viscous liquid and glassy solid dynamics is reviewed by a process of posing the key questions that need to be answered, and then providing the best answers available to the authors and their advisors at this time. The subject is divided into four parts, three of them dealing with behavior in different domains of temperature with respect to the glass transition temperature, Tg, and a fourth dealing with "short time processes." The first part tackles the high temperature regime T>Tg, in which the system is ergodic and the evolution of the viscous liquid toward the condition at Tg is in focus. The second part deals with the regime T~Tg, where the system is nonergodic except for very long annealing times, hence has time-dependent properties (aging and annealing). The third part discusses behavior when the system is completely frozen with respect to the primary relaxation process but in which secondary processes, particularly those responsible for "superionic" conductivity, and dopart mobility in amorphous silicon, remain active. In the fourth part we focus on the behavior of the system at the crossover between the low frequency vibrational components of the molecular motion and its high frequency relaxational components, paying particular attention to very recent developments in the short time dielectric response and the high Q mechanical response. ©2000 American Institute of Physics.

Formation of Glasses from Liquids and Biopolymers

CA Angell — 2007-05-20T17:03:13-00:00

Science, Vol. 267, No. 5206. (31 March 1995), pp. 1924-1935.

Glasses can be formed by many routes. In some cases, distinct polyamorphic forms are found. The normal mode of glass formation is cooling of a viscous liquid. Liquid behavior during cooling is classified between "strong" and "fragile," and the three canonical characteristics of relaxing liquids are correlated through the fragility. Strong liquids become fragile liquids on compression. In some cases, such conversions occur during cooling by a weak first-order transition. This behavior can be related to the polymorphism in a glass state through a recent simple modification of the van der Waals model for tetrahedrally bonded liquids. The sudden loss of some liquid degrees of freedom through such first-order transitions is suggestive of the polyamorphic transition between native and denatured hydrated proteins, which can be interpreted as single-chain glass-forming polymers plasticized by water and cross-linked by hydrogen bonds. The onset of a sharp change in d<r2>dT(<r2> is the Debye-Waller factor and T is temperature) in proteins, which is controversially indentified with the glass transition in liquids, is shown to be general for glass formers and observable in computer simulations of strong and fragile ionic liquids, where it proves to be close to the experimental glass transition temperature. The latter may originate in strong anharmonicity in modes ("bosons"), which permits the system to access multiple minima of its configuration space. These modes, the Kauzmann temperature TK, and the fragility of the liquid, may thus be connected. 10.1126/science.267.5206.1924

Water behaviourGlass transition in hyperquenched water? (reply)

Yuanzheng Yue — 2005-05-25T19:55:49-00:00

Nature, Vol. 435, No. 7041. (25 May 2005), pp. E1-E2.

Supercooled Liquids and Glasses

MD Ediger — 2006-04-07T00:58:56-00:00

J. Phys. Chem., Vol. 100, No. 31. (1 August 1996), pp. 13200-13212.

Ten questions on glassformers, and a real space `excitations' model with some answers on fragility and phase transitions

CA Angell — 2008-03-01T20:23:55-00:00

Journal of Physics: Condensed Matter, Vol. 12, No. 29. (2000), pp. 6463-6475.

We formulate ten questions, covering outstanding aspects of the phenomenology of glassforming liquids, which we believe must be properly answered by any successful theory of structural glassformers. The questions range across thermodynamic, mass transport and vibrational dynamics phenomena. While these questions will only be addressed properly by a collective variables approach (many aspects of which are reported in these proceedings) a number of them can be dealt with by use of simple physical models of appropriate form. Here we discuss one such model in which the existence of elementary configurational excitations of the amorphous quasilattice is proposed. These states, which may range from broken bonds to packing defects, can be excited independently in the majority of cases, or cooperatively in others. We summarize essential results of this model. These suggest that the source of the different fragilities in liquids (and the reason that structural glasses, alone among `glassy' systems, have marked heat capacity jumps at Tg) may lie largely in the way these configurational excitations couple to the vibrational modes of the system. The generation of low frequency modes in the density of vibrational states, as a direct consequence of the excitation of configurational states, explains why the quasi-elastic scattering from fragile liquids is so much stronger near and above Tg than in the case of strong liquids, and why the normal glass transition can be detected in picosecond time scale experiments. Interactions among the `excitations', or `defects', are taken into account using the one component system equivalent of the binary system `regular solution' model (which keeps only the first order term of the free energy of mixing expansion). We show that a liquid-liquid first order transition must occur at sufficiently strong defect-defect interactions. The highly overconstrained amorphous silicon quasilattice is a strong candidate for such a transition. We identify the `first order melting' of amorphous silicon, and the sudden, reproducible, termination of supercooling in experimental liquid silicon and germanium, with the phase transition predicted by the model. Many more cases of this phase transition may be anticipated, and a corresponding range of glasses with low residual entropies - approaching the `perfect' glass state - are predicted.