The low-temperature dynamics of ultraviscous liquids hold the key to understanding the nature of glass transition and relaxation phenomena, including the potential existence of an ideal thermodynamic glass transition. Unfortunately, existing viscosity models, such as the Vogel-Fulcher-Tammann (VFT) and Avramov-Milchev (AM) equations, exhibit systematic error when extrapolating to low temperatures. We present a model offering an improved description of the viscosity-temperature relationship for both inorganic and organic liquids using the same number of parameters as VFT and AM. The model has a clear physical foundation based on the temperature dependence of configurational entropy, and it offers an accurate prediction of low-temperature isokoms without any singularity at finite temperature. Our results cast doubt on the existence of a Kauzmann entropy catastrophe and associated ideal glass transition.modeling ͉ supercooled liquids ͉ configurational entropy ͉ relaxation P erhaps the most intriguing feature of a supercooled liquid is its dramatic rise in viscosity as it is cooled toward the glass transition. This sharp, super-Arrhenius increase is accompanied by very little change in the structural features observable by typical diffraction experiments. Several basic questions remain unanswered:1. Is the behavior universal (i.e., is the viscosity of all liquids described by the same underlying model)?2. Does the viscosity diverge at some finite temperature below the glass transition (i.e., is there a dynamic singularity)?3. Is the existence of a thermodynamic singularity the cause of the dramatic viscous slowdown?Answers to these questions are critical for understanding the behavior of deeply supercooled liquids. Unfortunately, equilibriumviscosity measurements cannot be carried out at temperatures much below the glass transition owing to the long structural relaxation time. It thus becomes critical to find a model that best describes the temperature dependence of viscosity by using the fewest possible number of fitting parameters (1, 2). Because two parameters are needed for a simple Arrhenius description, modeling of super-Arrhenius behavior requires a minimum of three parameters. We focus on three-parameter models only, with the goal of describing the universal physics of supercooled liquid viscosity in the most economical form possible.The most popular viscosity model is the Vogel-FulcherTammann (VFT) equation (3) log 10 ͑T, x͒ ϭ log 10 ϱ ͑x͒ ϩ A͑x͒where T is temperature, x is composition, and the three VFT parameters ( ϱ , A, and T 0 ) are obtained by fitting Eq. 1 to experimentally measured viscosity data. In the polymer science community, Eq. 1 is also known as the Williams-Landel-Ferry (WLF) equation (4). Although VFT has met with notable success for a variety of liquids, there is some indication that it breaks down at low temperatures (3, 5). Another successful three-parameter viscosity model is the Avramov-Milchev (AM) equation (6), derived based on an atomic hopping approach:where ϱ , , and ␣ are fittin...

The problem of glass relaxation under ambient conditions has intrigued scientists and the general public for centuries, most notably in the legend of flowing cathedral glass windows. Here we report quantitative measurement of glass relaxation at room temperature. We find that Corning® Gorilla® Glass shows measurable and reproducible relaxation at room temperature. Remarkably, this relaxation follows a stretched exponential decay rather than simple exponential relaxation, and the value of the stretching exponent (β=3/7) follows a theoretical prediction made by Phillips for homogeneous glasses.

We present a brief history of substrate glasses developed by Corning Incorporated (Corning) for use in Active matrix liquid crystal display (AMLCD) displays. The most basic attributes required of AMLCD substrates include thermal and mechanical stability, precise geometry control, a surface that is basically perfectly smooth, and no inclusions large enough to block a pixel in the final display. In addition, the glasses used as substrate materials must be essentially alkali‐free so that they do not interact chemically or electronically with thin‐film transistors (TFT). Thin, precision sheet was first made at Corning via the slot‐draw process, but was eventually moved to the fusion‐draw process; neither process was originally intended for this application. Alkali‐free glasses were originally developed for electronic applications and lamp envelopes, and considerable research was required to invent compositions that were compatible with the high‐viscosity fusion‐draw process. Examples of the technical challenges presented by the evolving industry requirements are provided, including eliminating arsenic from the substrate glass and reducing the dimensional change during high‐temperature processing of polysilicon‐based TFT.

We investigate the high-temperature limit of liquid viscosity by analyzing measured viscosity curves for 946 silicate liquids and 31 other liquids including metallic, molecular, and ionic systems. Our results show no systematic dependence of the high-temperature viscosity limit on chemical composition for the studied liquids. Based on the Mauro-Yue-Ellison-Gupta-Allan (MYEGA) model of liquid viscosity, the high-temperature viscosity limit of silicate liquids is 10 −2.93 Pa·s. Having established this value, there are only two independent parameters governing the viscosity-temperature relation, namely, the glass transition temperature and fragility index. It is also critical for understanding the relaxation characteristics of liquids, as in the well-known Angell plot 1 where the logarithm of viscosity, log 10 η, is plotted as a function of the T g -scaled inverse temperature, T g /T. Here, T g is the glass transition temperature, defined as the temperature at which the liquid viscosity equals 10 12 Pa·s, and T is absolute temperature. The slope of the Angell curve at T g defines the fragility index m,Fragility is a common measure of the slowing down of liquid dynamics upon cooling through the glass transition. According to Angell, 1 liquids can be classified as either "strong" or "fragile" depending on whether they exhibit an Arrhenius or super-Arrhenius scaling of viscosity with temperature, respectively. The degree of non-Arrhenius scaling varies greatly among different glass-forming liquids and reflects the second derivative of the viscosity curve with respect to inverse temperature. With the assumption of a universal hightemperature limit of viscosity, η ∞ , Angell proposed that this non-Arrhenius character is directly connected to the fragility index, m, a first-derivative property of the viscosity curve at T g . 2 However, the assumption of a universal high-temperature limit of viscosity, which enables this direct connection between first-and second-derivative properties, has not yet been validated by a systematic analysis of experimental data.In this Brief Report, we analyze viscosity-temperature curves of 946 silicate liquids and 31 other liquids, including water and silica, as well as borate, metallic, molecular, and ionic liquids. Our results show that there is no systematic dependence of η ∞ on composition and point to a narrow spread around η ∞ = 10 −2.93 Pa·s for silicate liquids. This result implies the existence of a universal high-temperature limit of viscosity, indicating that the fragility index m does have a direct relationship to the non-Arrhenius scaling of liquid viscosity (a measure of curvature), at least for silicate liquids. Our results indicate that there are only two independent parameters governing the viscosity of silicate liquids: T g and m.This simplifies the process for modeling the composition dependence of liquid viscosity and is an indication of the universal dynamics of silicate liquids at the high-temperature limit.To evaluate η ∞ , we analyze experimental viscosity data using ...

Nanoscale science and engineering, or "nanotechnology" as it is commonly known, has been a fundamental component of glass technology for hundreds if not thousands of years. Numerous examples can be found where our understanding of glass at the nanoscale level has proved transformational in the fabrication and application of this material. Among these are band theory, photosensitivity, ligand field theory, glass structure, microcrack theory, amorphous phase separation, controlled crystallization, and surface modification. Modern applications of glass in such diverse fields as energy, medicine, electronics, photonics, and communications are critically dependent on our awareness and appreciation of the intrinsic connections between glass and nanotechnology. Starting at the low end of the nanoscale, we review fundamental aspects of these connections with the intent of drawing attention to their role in both contemporary and future glass science and engineering. We argue that many of the most useful and interesting behaviors of glass are born at the nanoscale, even when we initially do not notice it.