Friction force effects on vertical manipulation of nanoparticles

In humid environment, a particles can be picked up from the substrate by the capillary force, such as in the colloidal probe of atomic force microscopy technique. In this paper, a model of the capillary bridge between spherical particles is used to study effect of the friction force in nanoparticles manipulation. Based on the Young-Laplace equation, Newtonian equation and adopted the constant volume boundary condition to calculate the particle motion, the friction force effects on nanoparticles manipulation are analyzed. The results show that the friction force has little effect on the particle motion, and the particle velocity decreases slightly in presence of the friction force. The friction force is opposed to the motion of the nanoparticle. As the tip velocity increases, there is a critical velocity beyond that the particle cannot be picked up from the substrate, and the critical velocity decreases in presence of the friction force. These provide a better understanding of the nanoparticle mechanical properties in humid environment.