Driving force for the swelling of montmorillonite as affected by surface charge and exchangeable cations: A molecular dynamic study

Revealing Expansion Mechanism of Cement-Stabilized Expansive Soil with Different Interlayer Cations through Molecular Dynamics Simulations

“…However, they could not appropriately reveal nanoscale interactions and energy variations. − By contrast, the molecular simulation method is an effective method to explain the interaction of energies between different phases at the nanoscale level. , In the past, the Monte Carlo (MC) and molecular dynamics (MD) methods have been used to investigate the interface interactions of water–clay–cations . Considering that montmorillonite (MMT) is one of the most common types of naturally existing clay minerals in expansive soil, MMT is usually employed as the representative mineral in the investigation of expansion property of expansive soil. , For example, Yi et al and Peng et al , studied the surface wettability and driving force of the MMT surface under the effects of exchangeable cations and surface charge using MD simulations. Their study indicated that the exchangeable ions on the surface of MMT played a leading role in determining the surface wettability.…”

Effect of Cations on Interlayer Water Dynamics in Cation-Exchanged Montmorillonites Studied by Nuclear Magnetic Resonance and X-ray Diffraction Techniques

“…Since substitution of divalent cations such as Mg 2+ for Al 3+ in the O sheet usually occurs, each interlayer space between the TOT layers allows the occupation of positively charged Na + to compensate the net negative charge on the TOT layer. , It is well known that crystalline swelling of the Na + -montmorillonite is initially driven by contact with water, and that existence of exchangeable cations in the interlayer spaces leads to a high cation exchange capacity of the montmorillonite. Effect of exchangeable cation species on the swelling of montmorillonite has been examined using experimental X-ray diffraction and gravimetric methods and computational methods, and it has been found that water uptake and swelling of montmorillonite change as a result of cation replacement, for example, Na + exchange by poorly hydrated monovalent cations such as K + and multivalent cations such as Mg 2+ , Ca 2+ , and La 3+ produce reduction and limitation, respectively, in the degree of swelling in contrast to that for Na + -montmorillonite. − Such phenomena have been related to ion hydration and interactions among water molecules, cations, and charged clay surfaces. Actually, to understand swelling phenomena at the molecular level, studies on the structure and dynamics of water and hydrated cations confined in the interlayer spaces of montmorillonites have been extensively performed by means of simulations as well as by various experimental techniques such as quasi-inelastic neutron scattering, nuclear magnetic resonance (NMR), and infrared spectroscopy, and impedance spectroscopy. − These have clarified that the number of layers (hydrated states), self-diffusion coefficients, rotational and translational motions, and residence time on clay surfaces of the confined water are strongly influenced by interlayer cations, relative humidity, and temperature.…”

Green Synthesized Montmorillonite/Carrageenan/Fe3O4 Nanocomposites for pH-Responsive Release of Protocatechuic Acid and Its Anticancer Activity

“…The Fe 3+ /Fe 2+ chloride salts and CR solution were added together into the MMT solution and stirred continuously to allow CR and Fe 3+ /Fe 2+ ions solutions to mix into the interlayer space of MMT. To allow for this phenomenon to occur, MMT powder was first dissolved into deionized water [26]. After that, the freshly prepared 1 M NaOH was added with continuous stirring to synthesize MMT/CR/Fe 3 O 4 -NCs.…”