Theory of lubrication due to collective pinning

In collective pinning theory, the problem of two three-dimensional solids in contact is at its critical dimension. This implies that when the disordered forces acting between the two solids at the interface are relatively strong, the force of static friction should be large, but at smaller values of these forces, the system switches over to a regime of weak static friction. It is argued that this provides a mechanism for the reduction of friction in boundary lubrication. Lubricant molecules reduce static friction by smoothing the roughness of the surface, thus allowing the force pushing the surfaces together to be supported by more points of contact, which can switch the interface from the strong- to weak-static-friction regime.