Investigation of the interface stick-slip friction behavior of clay nanoplatelets by molecular dynamics simulations

As lamella and porous materials, the failure of clay soil is closely related to the microscale friction features between nano minerals sheets. This study delves into the microscale interface stick-slip friction behavior of clay minerals, with a particular focus on kaolinite and halloysite models, under varying hydrostatic pressure conditions. The research unveils several significant discoveries. Firstly, under hydrostatic pressure, the mechanical properties of clay minerals perpendicular to the mineral platelet weaken, accompanied by a gradual reduction in the space occupied by interlayer water molecules. As pressure increases, these molecules assemble into "water molecular clusters", resulting in the formation of two or three layers of water molecular films. At 6 GPa, interlayer water nearly reaches a state of stagnation. Secondly, both kaolinite and halloysite exhibit "stick-slip friction behavior" during shearing, with rising hydrostatic pressure intensifying interatomic interactions and augmenting shear stress fluctuations. Lastly, the calculated friction coefficients (μ) for the three systems (kaolinite –7 Å, halloysite –8.6 Å, and halloysite –10 Å) are 0.035, 0.048, and 0.033, respectively, while the friction angles (φ) are 2.270, 2.900, and 2.263. The cohesion values (C) for these systems, obtained through different methods, demonstrate consistency. These findings advance the understanding of clay mineral behavior under varying conditions and contribute valuable insights to the microscale failure mechanism of clay soil.