The Science & Technology
of Glass
Cambridge - Monday 4th to
Wednesday 6th September 2017

Edwin Flikkema
<[email protected]>

article posted 22 May 2017

Edwin Flikkema is a lecturer at the Department of Physics at Aberystwyth University in Wales in the United Kingdom. Born in the Netherlands, he studied Theoretical Physics at the University of Groningen. He obtained a PhD on the subject of Monte Carlo simulation in polymer physics from the same university in 2002. He has worked as a postdoc at the Delft University of Technology, the University of Barcelona and the University of Cambridge. Since 2008 he is working as a lecturer at Aberystwyth University, specialising in computational materials science: structure prediction of atomic clusters, simulation of glass-forming materials and foams.

Structure and ion dynamics of alkali-silicates: a simulation study
Edwin Flikkema*, Wenlin Chen & Neville Greaves

Department of Physics, Aberystwyth University, Penglais, Aberystwyth SY23 3BZ, United Kingdom

Alkali-silicates form a class of glass-forming materials that is ubiquitous in science and engineering. Alkali-silicates consist of silica (SiO2) with alkali-oxides such as Na2O and K2O added, which act as network modifiers. The excess oxygen leads to the introduction of Non Bridging Oxygens, partially breaking up the silica network, forming pores where the alkali ions tend to reside. This simulation study focusses on alkali-silicates in the (supercooled) liquid and glassy state. Mixtures of sodium-disilicate (Na2O-(SiO2)2) and potassium-disilicate (K2O-(SiO2)2) have been studied using Molecular Dynamics simulations. At the range of temperatures studied, the silica network is mostly static while the alkali ions are relatively free to move. Experimentally, such mixtures show the Mixed Alkali Effect (MAE), meaning a non-linear dependence of the mobility of the alkali ions on the sodium/potassium ratio, where the dynamics slows down when multiple alkali species are present in the system. One of the key objectives of this study is to see if this effect can be reproduced in simulation. The simulations show a MAE in the form of a minimum in the diffusion constant of the alkali ions at roughly a 50/50 sodium/potassium ratio. The alkali dynamics has been studied using various techniques. Intermediate scattering functions have been obtained for a range of temperatures and compositions, showing the ballistic, diffusive and intermediate regimes. Pareto plots have been used to quantify the dynamic heterogeneity of the alkali ions. The ultimate aim is to be able to understand the origin of the Mixed Alkali Effect at the atomic scale.

If time permits, recent results on the amorphisation of zeolites and Metal-Organic-Frameworks will be presented.