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.
Original language | English |
---|---|
Pages (from-to) | 197-211 |
Journal | Clay Minerals |
Volume | 51 |
Issue number | 2 |
DOIs | |
Publication status | Published - 2016 |
MoE publication type | A1 Journal article-refereed |
Keywords
- molecular dynamics
- density functional theory
- layer charge
- montmorillonite
- swelling
- diffusion