Journal
JOURNAL OF THE AMERICAN CERAMIC SOCIETY
Volume 104, Issue 12, Pages 6227-6241Publisher
WILEY
DOI: 10.1111/jace.18006
Keywords
equilibrium viscosity; glass; glass transition; molecular dynamics simulation; nonequilibrium viscosity; potential energy; shear modulus; the shoving model
Categories
Funding
- National Science Foundation [DMR-1255378, DMR-1508410, DMR-2015557]
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This study presents a novel method to calculate viscosity of liquid and glass, which is verified through molecular dynamics simulations. The model can reliably estimate equilibrium and nonequilibrium viscosities of glass, providing important theoretical support for studying glass transition and relaxation of amorphous solids.
Temperature-dependent viscosity is critical to decipher two profound questions in condensed matter physics, namely the glass transition and the relaxation of amorphous solids. However, direct measurement of viscosity over a large temperature range is extremely difficult. Here, using classical molecular dynamics (MD) simulations, we report a novel method to calculate the equilibrium viscosity of supercooled liquid both above and below the glass transition temperature (T-g) and to estimate the nonequilibrium viscosity of glass down to room temperature. Based on the shoving model, we derived an analytical formula showing that the shear viscosity in logarithmic scale changes linearly with the shear-induced variation in shear modulus or potential energy of the glass-forming system. The shear viscosity as a function of steady-state potential energy of liquid under different shear strain rates can be directly calculated in MD simulations; together with its equilibrium potential energy, one can extrapolate the zero-strain-rate equilibrium viscosity. We verified the proposed model by reliably calculating equilibrium viscosity near T g of four glass-forming systems (Kob-Andersen system, silica, Cu45.5Zr45.5Al9, and silicon) with different fragilities. Furthermore, our model can estimate the nonequilibrium viscosity of glass below T-g; the upper-bound nonequilibrium viscosity of amorphous silica and silicon at room temperature are calculated to be similar to 10(32 )and 10(25) Pa.s, respectively.
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