Long-Range Ionic and Short-Range Hydration Effects Govern Strongly Anisotropic Clay Nanoparticle Interactions

Area of Science:

• * Environmental Science
• * Materials Science
• * Physical Chemistry

Background:

• * Clay particle aggregation in aqueous solutions is vital for environmental and technological processes.
• * Atomistic-level understanding of these interactions is limited due to complex interplay of forces.
• * Key forces include solvent-mediated electrostatic, hydrogen bonding, and dispersion interactions.

Purpose of the Study:

• * To investigate the atomistic interactions between model kaolinite nanoparticles in aqueous solutions.
• * To elucidate the role of electrostatic and hydration forces in nanoparticle aggregation.
• * To provide insights for improving coarse-grained models of clay aggregation.

Main Methods:

• * Extensive classical molecular dynamics simulations were performed.
• * Enhanced sampling techniques were incorporated into the simulations.
• * Simulations were conducted in both pure and salty water environments.

Main Results:

• * Highly anisotropic interactions were observed, varying with nanoparticle orientation.
• * Electrostatic effects dominate interactions at separations greater than 1.5 nm.
• * Water hydration structure becomes critical at smaller nanoparticle separations.

Conclusions:

• * Clay nanoparticle interactions exhibit significant complexity and anisotropy.
• * Both electrostatic forces and hydration structure play critical roles in aggregation.
• * Findings necessitate refinement of coarse-grained models for accurate clay aggregation prediction.