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 dT( 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 T(K), and the fragility of the liquid, may thus be connected.

https://science.sciencemag.org/content/sci/267/5206/1924.full.pdf

Formation of glasses from liquids and biopolymers.

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 ,i n 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.@S0021-8979~00!02213-1#

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1065&context=mse_pubs

Relaxation in glassforming liquids and amorphous solids

https://hal.archives-ouvertes.fr/hal-00120432/document

Raman Spectroscopy of Nanomaterials: How Spectra Relate to Disorder, Particle Size and Mechanical Properties

The nature of boson peak in Raman scattering in glasses

A model assuming a non-continuous structure of glasses is established to interpret the inelastic neutron scattering and Raman scattering. The 'boson' peak in Raman scattering is related to the vibrational density of states 'excess'. These two related features are a result of vibrations localized in the blobs that compose the glass. Size distributions of the blobs are deduced from neutron and Raman scatterings.

https://iopscience.iop.org/article/10.1088/0953-8984/2/51/001/pdf

Vibrational dynamics and the structure of glasses

An elastic continuum model is presented for Brillouin scattering by an amorphous solid. The assumption that light scatters on distorted plane wave acoustic phonons leads to the prediction that the scattered intensity plotted as a function of the frequency transfer Ωo consists of the usual Brillouin peaks plus a background which, a t room temperature, goes like Ωo; for small Ωo, but rises less steeply for larger Ωo, and may even bend over within the range of the validity of the model, depending on the correlation lengths for spatial fluctuations due to disorder and on the speeds of sound. For the case of a-Si, additional results are obtained with the help of existing experimental measurements.



Es wird die Brillouinstreuung in a morphen Snbstanzen an einem elastischen Kontinuums-modell diskutiert. Die Annahme, das Licht an durch deformierte ebene Wellen beschriebenen akustischen Phononen gestreut wird, fiihrt zu folgenden Aussagen. Die Streuintensitiit als Funktion der Frequenzverschiebung besteht aus den ublichen Brillouin-Peaks und einem Hintergrund, der, bei Raumtemperaturen, fur kleine Ωo proportional zu Ω 2o ist. Mit wachsendem Ω o wachst der Hintergrund dam schwacher als Ω2o. Jc nach den Werten der Korrelationslangen fur raumliche Fluktuationen und der Schallgeschwindigkeiten kanner im Giiltigkeitsbereich des Modells sogar nach Erreichen eines Maximums wieder abfallen. ZusaItzliche Aussagen werden fur den Fall von a-Si unter Ausnutzung existierender Messungen gemacht.

W. Brenig

Papers

Model for Brillouin Scattering in Amorphous Solids