• Olin, Markus
• Seppälä, Anniina
• Puhakka, Eini

Abstract

The swelling and cation exchange properties ofmontmorillonite are fundamental in a wide range ofapplications ranging from nanocomposites to catalyticcracking of hydrocarbons. The swelling results fromseveral factors and, though widely studied, informationon 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 informationon the swelling of montmorillonite. Molecular dynamics(MD) was used to investigate the swelling properties ofmontmorillonites with different layer charges andinterlayer cationic compositions. Molecular dynamicscalculations, with CLAYFF force field, consider threelayer charges (-1.0, -0.66 and -0.5 e per unit cell)arising from octahedral substitutions and interlayercounterions of Na, K and Ca. The swelling curves obtainedshowed that smaller layer charge results in greaterswelling but the type of the interlayer cation also hasan effect. The DFT calculations were also seen to predictlarger d values than MD. The formation of 1, 2 and 3water molecular layers in the interlayer spaces wasobserved. Finally, the data from MD calculations wereused to predict the self-diffusion coefficients ofinterlayer water and cations in differentmontmorillonites and in general the coefficient increasedwith increasing water content and with decreasing layercharge.

Topics

• nanocomposite
• density
• impedance spectroscopy
• theory
• molecular dynamics
• density functional theory