(221e) Hysteresis, Force Oscillations and Non-Equilibrium Effects in the Adhesion of Nanoparticles to Atomically Smooth Surfaces

We discuss hysteretic effects and non-equilibrium aspects of particle adhesion on the walls of a nano-sized fluid-filled channel. The force on the suspended particle is found to depend not only on its radial position and the wetting properites of the fluid, but also on its history, even when the approaching/receding motion toward the wall occurs on time scales much longer than the spontaneous adsorption time. The hysteresis is associated with changes in fluid density in the gap between particle and wall, and these structural rearrangements persist over surprisingly long times. In addition, the force oscillate with distance when the orientation of the particle is fixed, but not if it is alllowed to rotate freely. Adsorbed particles are trapped in free energy minima in equilibrium, but if the particle is forced along the channel the resulting stick-slip motion alters the fluid structure and allows its release.