Nanoscale interfacial tribology behavior between clay and sand : effects of cations, normal load and sliding velocity

Abstract

The interfacial tribology between clay and sand could significantly affect the mechanical stability of soil structures, while it remains unclear in the microscale. In this study, molecular dynamics (MD) simulation method has been employed to investigate the nanoscale friction behavior between quartz and montmorillonite at dry state, where quartz and montmorillonite are the common components of sand and clay, respectively. The effects of normal load, interlayer cations, and sliding velocity on their frictional behavior were discussed. The simulation results indicated that the stick–slip effect during friction process was gradually weakened with the increasing sliding velocity or decreasing normal load. The shear stress increased with the increasing normal load, exhibiting an approximately linear relationship. The order of friction coefficients of montmorillonite-quartz with different interlayer cations was Ca2+ > Zn2+ > Ni2+ > Pb2+ > Li+ > Rb+ > Cs+ > K+, illustrating that the friction coefficient of montmorillonite-quartz systems with divalent cations was greater than that with monovalent cations. The friction angle of montmorillonite-quartz with different interlayer cations varies from 6.96 to 17.28°. Moreover, the friction load rose linearly with the sliding velocity, indicating that nanoscale friction was velocity-dependent.