Adhesion and friction of dry-coated nano-rough particles

The adhesion and friction properties of two contacting surfaces with nanoscale roughness, which are formed by depositing nanoparticles (guest particles) on the surfaces of micro-sized particles (host particles), are investigated. Previous mechanistic contact models for nano-rough surfaces examined the influence of the surface area coverage (SAC) under several limiting assumptions and also did not consider the impact of SAC on frictional forces. In this work, the impact of dominant contacts is examined via simulations and a probabilistic contact model. Simulation results, capturing the main features observed in the physical experiments, indicate that depending on the extent of SAC by nanoparticles, the adhesion and friction forces can be dominated by the host-host (HH), host-guest (HG), or guest-guest (GG) contacts. In contrast to the previous deterministic model, these transitions are smoother and the critical SAC for the transition to GG contacts from HG contacts is lower than previously reported values. Moreover, the existence of optimal SAC leads to the minimum adhesion and friction forces. Then a probabilistic model capable of predicting the probabilities of HH, HG, and GG contacts as a function of the SAC is proposed and formulated. The theoretical predictions match well with the numerical simulation results.