The Dynamics of Silica Melts under High Pressure: Mode-Coupling Theory Results

TL;DR

This study applies mode-coupling theory to model the high-pressure dynamics of silica melts, successfully explaining viscosity behavior and structural changes observed in simulations and experiments.

Contribution

It demonstrates that mode-coupling theory can qualitatively reproduce the viscosity minimum and structural transitions in silica melts under high pressure.

Findings

Reproduces the viscosity minimum as a function of pressure.

Explains the structural transition from tetrahedral to caged arrangements.

Qualitative agreement with molecular dynamics simulation results.

Abstract

The high-pressure dynamics of a computer-modeled silica melt is studied in the framework of the mode-coupling theory of the glass transition (MCT) using static-structure input from molecular-dynamics (MD) computer simulation. The theory reproduces the experimentally known viscosity minimum (diffusivity maximum) as a function of density or pressure and explains it in terms of a corresponding minimum in its critical temperature. This minimum arises from a gradual change in the equilibrium static structure which shifts from being dominated by tetrahedral ordering to showing the cageing known from high-density liquids. The theory is in qualitative agreement with computer simulation results.