Viscosity computed using the Network model expression, <b>Eq. (16)</b>, with the four TSP trajectories shown in <b>Fig. 2</b> as input.

<p>Results for each trajectory are denoted by a different symbol, squares for trajectory I, triangle for II, inverted triangles for III, and circles for trajectory IV. Solid curve is a spline fit to all the calculated viscosities.</p

Comparison of an effective temperature-dependent activation barrier obtained from experimental data (symbols) [<b>4</b>] with similarly reduced results of the Network model (solid curve).

<p>The value of <i>T</i>* is 0.63 for the Network model.</p

Data used in the Network model calculation.

<p>(a) Average inherent structure (IS) energy of BLJ liquid as a function of temperature, (b) Distributions of IS energies at four temperatures, 1.0, 0.5, 0.4, and 0.3, (c) Four TSP trajectories initialized at different energy minima (right panel).</p

Experimental validation of the Network model.

<p>Solid line indicates the viscosity of BLJ liquid calculated by the Network model. Symbols are experimental data on fragile glass formers <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0017909#pone.0017909-Angell1" target="_blank">[3]</a>.</p

Pressure-Induced Changes in Interdiffusivity and Compressive Stress in Chemically Strengthened Glass

Glass exhibits a significant change in properties when subjected to high pressure because the short- and intermediate-range atomic structures of glass are tunable through compression. Understanding the link between the atomic structure and macroscopic properties of glass under high pressure is an important scientific problem because the glass structures obtained via quenching from elevated pressure may give rise to properties unattainable under standard ambient pressure conditions. In particular, the chemical strengthening of glass through K⁺-for-Na⁺ ion exchange is currently receiving significant interest due to the increasing demand for stronger and more damage-resistant glass. However, the interplay among isostatic compression, pressure-induced changes in alkali diffusivity, compressive stress generated through ion exchange, and the resulting mechanical properties are poorly understood. In this work, we employ a specially designed gas pressure chamber to compress bulk glass samples isostatically up to 1 GPa at elevated temperature before or after the ion exchange treatment of a commercial sodium–magnesium aluminosilicate glass. Compression of the samples prior to ion exchange leads to a decreased Na⁺–K⁺ interdiffusivity, increased compressive stress, and slightly increased hardness. Compression after the ion exchange treatment changes the shape of the potassium–sodium diffusion profiles and significantly increases glass hardness. We discuss these results in terms of the underlying structural changes in network-modifier environments and overall network densification