Effect of layer charge on the crystalline swelling of Na+, K+ and Ca2+ montmorillonites : DFT and molecular dynamics studies

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Seppälä , A , Puhakka , E & Olin , M 2016 , ' Effect of layer charge on the crystalline swelling of Na+, K+ and Ca2+ montmorillonites : DFT and molecular dynamics studies ' , Clay Minerals , vol. 51 , no. 2 , pp. 197-211 . https://doi.org/10.1180/claymin.2016.051.2.07

Title: Effect of layer charge on the crystalline swelling of Na+, K+ and Ca2+ montmorillonites : DFT and molecular dynamics studies
Author: Seppälä, Anniina; Puhakka, Eini; Olin, Markus
Contributor: University of Helsinki, Department of Chemistry
Date: 2016-05
Language: eng
Number of pages: 15
Belongs to series: Clay Minerals
ISSN: 0009-8558
URI: http://hdl.handle.net/10138/185063
Abstract: The swelling and cation exchange properties of montmorillonite are fundamental in a wide range of applications ranging from nanocomposites to catalytic cracking of hydrocarbons. The swelling results from several factors and, though widely studied, information on the effects of a single factor at a time is lacking. In this study, density functional theory (DFT) calculations were used to obtain atomic-level information on the swelling of montmorillonite. Molecular dynamics (MD) was used to investigate the swelling properties of montmorillonites with different layer charges and interlayer cationic compositions. Molecular dynamics calculations, with CLAYFF force field, consider three layer charges (-1.0, -0.66 and -0.5 e per unit cell) arising from octahedral substitutions and interlayer counterions of Na, K and Ca. The swelling curves obtained showed that smaller layer charge results in greater swelling but the type of the interlayer cation also has an effect. The DFT calculations were also seen to predict larger d values than MD. The formation of 1, 2 and 3 water molecular layers in the interlayer spaces was observed. Finally, the data from MD calculations were used to predict the self-diffusion coefficients of interlayer water and cations in different montmorillonites and in general the coefficient increased with increasing water content and with decreasing layer charge.
Subject: molecular dynamics
density functional theory
layer charge
montmorillonite
swelling
diffusion
CLAY-MINERALS
EXCHANGED FORMS
WATER-VAPOR
ADSORPTION
SIMULATION
DESORPTION
SURFACE
MECHANISM
SMECTITES
MODELS
116 Chemical sciences
1171 Geosciences
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